Posts by Jai Ganesh

Jai Ganesh · This is Cool

X-ray

Gist

An X-ray is a quick, painless test that captures images of the structures inside the body — particularly the bones. X-ray beams pass through the body. These beams are absorbed in different amounts depending on the density of the material they pass through.

The full name for "X-ray" is X-radiation, referring to its nature as a form of high-energy electromagnetic radiation, with the 'X' signifying its unknown nature when first discovered by Wilhelm Conrad Röntgen in 1895.

In many languages, it's also called Röntgen radiation, honoring its discoverer. Through experimentation, he found that the mysterious light would pass through most substances but leave shadows of solid objects. Because he did not know what the rays were, he called them 'X,' meaning 'unknown,' rays.

Summary

An X-ray is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ranging from 10 nanometers to 10 picometers, corresponding to frequencies in the range of 30 petahertz to 30 exahertz (3×{10}^{16} Hz to 3×{10}^{19} Hz) and photon energies in the range of 100 eV to 100 keV, respectively.

X-rays were discovered in 1895 by the German scientist Wilhelm Conrad Röntgen, who named it X-radiation to signify an unknown type of radiation.

X-rays can penetrate many solid substances such as construction materials and living tissue, so X-ray radiography is widely used in medical diagnostics (e.g., checking for broken bones) and materials science (e.g., identification of some chemical elements and detecting weak points in construction materials). However X-rays are ionizing radiation and exposure can be hazardous to health, causing DNA damage, cancer and, at higher intensities, burns and radiation sickness. Their generation and use is strictly controlled by public health authorities.

Details

X-rays are a way for healthcare providers to get pictures of the inside of your body. X-rays use radiation to create black-and-white images that a radiologist reads. Then, they send a report to your provider. X-rays are mostly known for looking at bones and joints. But providers can use them to diagnose other conditions, too.

Overview:

What is an X-ray?

An X-ray is a type of medical imaging that uses radiation to take pictures of the inside of your body. We often think of an X-ray as something that checks for broken bones. But X-ray images can help providers diagnose other injuries and diseases, too.

Many people think of X-rays as black-and-white, two-dimensional images. But modern X-ray technology is often combined with other technologies to make more advanced types of images.

Types of X-rays

Some specific imaging tests that use X-rays are:

* Bone density (DXA) scan: This test captures X-ray images while also checking the strength and mineral content of your bones.
* CT scan (computed tomography): CT scans use X-ray and computers to create 3D images of the inside of your body.
* Dental X-ray: A dental provider takes X-rays of your mouth to look for cavities or issues with your gums.
* Fluoroscopy: This test uses a series of X-rays to show the inside of your body in real time. Providers use it to help diagnose issues with specific body parts. They also use it to help guide certain procedures, like an angiogram.
* Mammogram: This is a special X-ray of your breasts that shows irregularities that could lead to breast cancer.

X-rays can help healthcare providers diagnose various conditions in your body. Some of the most common areas on your body to get an X-ray are:

* Abdominal X-ray: This X-ray helps providers evaluate parts of your digestive system and diagnose conditions like kidney stones and bladder stones.
* Bone X-ray: You might get a bone X-ray if your provider suspects you have a broken bone, dislocated joint or arthritis. Images from bone X-rays can also show signs of bone cancer or infection.
* Chest X-ray: Your provider might order a chest X-ray if you have symptoms like chest pain, shortness of breath or a cough. It can look for signs of infection in your lungs or congestive heart failure.
* Head X-ray: These can help providers see skull fractures from head injuries or conditions that affect how the bones in your skull form, like craniosynostosis.
* Spine X-ray: A provider can use a spine X-ray to look for arthritis and scoliosis.

Test Details:

How do X-rays work?

X-rays work by sending beams of radiation through your body to create images on an X-ray detector nearby. Radiation beams are invisible, and you can’t feel them.

As the beams go through your body, bones, soft tissues and other structures absorb radiation in different ways:

* Solid or dense tissues (like bones and tumors) absorb radiation easily, so they appear bright white on the image.
* Soft tissues (like organs, muscle and fat) don’t absorb radiation as easily, so they appear in shades of gray on the X-ray.

A radiologist interprets the image and writes a report for the physician who ordered the X-ray. They make note of anything that’s abnormal or concerning. Then, your healthcare provider shares the results with you.

How do I prepare?

Preparation for an X-ray depends on the type of X-ray you’re getting. Your provider may ask you to:

* Remove metal objects like jewelry, hairpins or hearing aids (metal can interfere with X-rays and make the results inaccurate)
* Wear comfortable clothing or change into a gown before the X-ray

Tell your healthcare provider about your health history, allergies and any medications you’re taking. Let them know if you’re pregnant or think you could be.

What can I expect during an X-ray?

The exact steps of an X-ray depend on the kind you’re getting. In general, your provider will follow these steps during an X-ray:

* They’ll ask you to sit, stand or lie down on a table. In the past, your provider may have covered you with a lead shield (apron), but new evidence suggests that they aren’t necessary.
* Your provider will position the camera near the body part that they’re getting a picture of.
* Then, they’ll move your body or limbs in different positions and ask you to hold still. They may also ask you to hold your breath for a few seconds so the images aren’t blurry.

Sometimes, children can’t stay still long enough to produce clear images. Your child’s provider may recommend using a restraint during an X-ray. The restraint helps your child stay still and reduces the need for retakes. The restraints don’t hurt and won’t harm your child.

What happens after?

Most of the time, there aren’t any restrictions on what you can do after an X-ray. You can go back to your typical activities.

What are the risks or side effects of X-rays?

X-rays are safe and low risk.

X-rays use a safe and small amount of radiation — not much more than the naturally occurring radiation you get in your daily life. For instance, a dental X-ray exposes you to about the same amount of background radiation you’d get in one day.

X-ray radiation is usually safe for adults. But it can be harmful to a fetus. If you’re pregnant, your provider may choose another imaging test, like ultrasound.

Additional Information:

Overview

An X-ray is a quick, painless test that captures images of the structures inside the body — particularly the bones.

X-ray beams pass through the body. These beams are absorbed in different amounts depending on the density of the material they pass through. Dense materials, such as bone and metal, show up as white on X-rays. The air in the lungs shows up as black. Fat and muscle appear as shades of gray.

For some types of X-ray tests, a contrast medium — such as iodine or barium — is put into the body to get greater detail on the images.

Why it's done:

X-ray technology is used to examine many parts of the body.

Bones and teeth

* Fractures and infections. In most cases, fractures and infections in bones and teeth show up clearly on X-rays.
* Arthritis. X-rays of the joints can show evidence of arthritis. X-rays taken over the years can help your healthcare team tell if your arthritis is worsening.
* Dental decay. Dentists use X-rays to check for cavities in the teeth.
* Osteoporosis. Special types of X-ray tests can measure bone density.
* Bone cancer. X-rays can reveal bone tumors.

Chest

* Lung infections or conditions. Evidence of pneumonia, tuberculosis or lung cancer can show up on chest X-rays.
* Breast cancer. Mammography is a special type of X-ray test used to examine breast tissue.
* Enlarged heart. This sign of congestive heart failure shows up clearly on X-rays.
* Blocked blood vessels. Injecting a contrast material that contains iodine can help highlight sections of the circulatory system so they can be seen easily on X-rays.

Abdomen

* Digestive tract issues. Barium, a contrast medium delivered in a drink or an enema, can help show problems in the digestive system.
* Swallowed items. If a child has swallowed something such as a key or a coin, an X-ray can show the location of that object.

X-ray technology is used to examine many parts of the body.

Risks:

Radiation exposure

Some people worry that X-rays aren't safe. This is because radiation exposure can cause cell changes that may lead to cancer. The amount of radiation you're exposed to during an X-ray depends on the tissue or organ being examined. Sensitivity to the radiation depends on your age, with children being more sensitive than adults.

Generally, however, radiation exposure from an X-ray is low, and the benefits from these tests far outweigh the risks.

However, if you are pregnant or suspect that you may be pregnant, tell your healthcare team before having an X-ray. Though most diagnostic X-rays pose only small risk to an unborn baby, your care team may decide to use another imaging test, such as ultrasound.

Contrast medium

In some people, the injection of a contrast medium can cause side effects such as:

* A feeling of warmth or flushing.
* A metallic taste.
* Lightheadedness.
* Nausea.
* Itching.
* Hives.

Rarely, severe reactions to a contrast medium occur, including:

* Very low blood pressure.
* Difficulty breathing.
* Swelling of the throat or other parts of the body.

How you prepare:

Different types of X-rays require different preparations. Ask your healthcare team to provide you with specific instructions.

What to wear

In general, you undress whatever part of your body needs examination. You may wear a gown during the exam depending on which area is being X-rayed. You also may be asked to remove jewelry, eyeglasses and any metal objects because they can show up on an X-ray.

Contrast material

Before having some types of X-rays, you're given a liquid called contrast medium. Contrast mediums, such as barium and iodine, help outline a specific area of your body on the X-ray image. You may swallow the contrast medium or receive it as an injection or an enema.

What you can expect:

During the X-ray

X-rays are performed at medical offices, dentists' offices, emergency rooms and hospitals — wherever an X-ray machine is available. The machine produces a safe level of radiation that passes through the body and records an image on a specialized plate. You can't feel an X-ray.

A technologist positions your body to get the necessary views. Pillows or sandbags may be used to help you hold the position. During the X-ray exposure, you remain still and sometimes hold your breath to avoid moving so that the image doesn't blur.

An X-ray procedure may take just a few minutes for a simple X-ray or longer for more-involved procedures, such as those using a contrast medium.

Your child's X-ray

If a young child is having an X-ray, restraints or other tools may be used to keep the child still. These won't harm the child and they prevent the need for a repeat procedure, which may be necessary if the child moves during the X-ray exposure.

You may be allowed to remain with your child during the test. If you remain in the room during the X-ray exposure, you'll likely be asked to wear a lead apron to shield you from unnecessary X-ray exposure.

After the X-ray

After an X-ray, you generally can resume usual activities. Routine X-rays usually have no side effects. However, if you're given contrast medium before your X-ray, drink plenty of fluids to help rid your body of the contrast. Call your healthcare team if you have pain, swelling or redness at the injection site. Ask your team about other symptoms to watch for.

Results:

X-rays are saved digitally on computers and can be viewed on-screen within minutes. A radiologist typically views and interprets the results and sends a report to a member of your healthcare team, who then explains the results to you. In an emergency, your X-ray results can be made available in minutes.

Jai Ganesh · Dark Discussions at Cafe Infinity

2427) Ilya Frank

Gist:

Work

In certain media the speed of light is lower than in a vacuum and particles can travel faster than light. One result of this was discovered in 1934 by Pavel Cherenkov, when he saw a bluish light around a radioactive preparation placed in water. Ilya Frank and Igor Tamm explained the phenomenon in 1937. On their way through a medium, charged particles disturb electrons in the medium. When these resume their position, they emit light. Normally this does not produce any light that can be observed, but if the particle moves faster than light, a kind of backwash of light appears.

Summary

Ilya Mikhaylovich Frank (born October 10 [October 23, New Style], 1908, St. Petersburg, Russia—died June 22, 1990, Moscow, Russia, U.S.S.R.) was a Soviet winner of the Nobel Prize for Physics in 1958 jointly with Pavel A. Cherenkov and Igor Y. Tamm, also of the Soviet Union. He received the award for explaining the phenomenon of Cherenkov radiation.

After graduating from Moscow State University in 1930, Frank worked at the Leningrad Optical Institute. He returned to Moscow to work at the P.N. Lebedev Physical Institute (1934–70) and from 1940 was a professor at Moscow State University.

In 1937 Frank and Tamm provided the theoretical explanation of Cherenkov radiation, an effect discovered by Cherenkov in 1934 in which light is emitted when charged particles travel through an optically transparent medium at speeds greater than the speed of light in that medium. The effect led to the development of Cherenkov counters for detecting and measuring the velocity of high-speed particles, allowing discoveries of new elementary particles such as the antiproton.

Frank later worked on theoretical and experimental nuclear physics and the design of reactors, and from 1957 he headed the neutron laboratory at the Joint Institute for Nuclear Research in Dubna. In 1946 Frank was elected a corresponding member, and in 1968 a full member, of the U.S.S.R. Academy of Sciences.

Details

Ilya Mikhailovich Frank (23 October 1908 – 22 June 1990) was a Soviet physicist who received the 1958 Nobel Prize in Physics, jointly with Pavel Alekseyevich Cherenkov and Igor Y. Tamm, also of the Soviet Union. He received the award for his work in explaining the phenomenon of Cherenkov radiation. He received the Stalin prize in 1946 and 1953 and the USSR state prize in 1971.

Life and career

Ilya Frank was born on 23 October 1908 in St. Petersburg. His father, Mikhail Lyudvigovich Frank, was a talented mathematician descended from a Jewish family, while his mother, Yelizaveta Mikhailovna Gratsianova, was a Russian Orthodox physician. His father participated in the student revolutionary movement, and as a result was expelled from Moscow University. After the October Revolution, he was reinstated and appointed professor. Ilya's uncle, Semyon Frank, a philosopher, was expelled from Soviet Russia in 1922 together with 160 other intellectuals. Ilya had one elder brother, Gleb Mikhailovich Frank, who became an eminent biophysicist and member of the Academy of Sciences of the USSR.

Ilya Frank studied mathematics and theoretical physics at Moscow State University. From his second year he worked in the laboratory of Sergey Ivanovich Vavilov, whom he regarded as his mentor. After graduating in 1930, on recommendation of Vavilov, he started working at the State Optical Institute in Leningrad. There he wrote his first publication—about luminescence— with Vavilov. The work he did there would form the basis of his doctoral dissertation in 1935.

In 1934, Frank moved to the Institute of Physics and Mathematics of the USSR Academy of Sciences (which shortly would be moved to Moscow, where it was transformed into the Institute of Physics). Here he started working on nuclear physics, a new field for him. He became interested in the effect discovered by Pavel Cherenkov, that charged particles moving through water at high speeds emit light. Together with Igor Tamm, he developed a theoretical explanation: the effect occurs when charged particles travel through an optically transparent medium at speeds greater than the speed of light in that medium, causing a shock wave in the electromagnetic field. The amount of energy radiated in this process is given by the Frank–Tamm formula.

The discovery and explanation of the effect resulted in the development of new methods for detecting and measuring the velocity of high-speed nuclear particles and became of great importance for research in nuclear physics. Cherenkov radiation is also widely used in biomedical research for detection of radioactive isotopes. In 1946, Cherenkov, Vavilov, Tamm, and Frank were awarded a Stalin Prize for their discovery, and 1958 Cherenkov, Tamm, and Frank received the Nobel Prize in Physics.

In 1944, Frank was appointed professor and became head of a department at the Institute of Physics and of the Nuclear Physics Laboratory (which was later transferred to the Institute of Nuclear Research). Frank's laboratory was involved in the (then secret) study of nuclear reactors. In particular, they studied the diffusion and thermalization of neutrons.

In 1957, Frank also become director of the Laboratory of Neutron Physics at the Joint Institute for Nuclear Research. The laboratory was based on the neutron fast-pulse reactor (IBR) then under construction at the site. Under Frank's supervision the reactor was used in the development of neutron spectroscopy techniques.

Personal life and death

Frank married the noted historian, Ella Abramovna Beilikhis, in 1937. Their son, Alexander, was born in the same year, and would continue much of the studies of his father as a physicist.

Frank died on 22 June 1990 in Moscow at the age 81.

Jai Ganesh · This is Cool

2489) Specific Gravity

Gist

Specific gravity (SG) is the ratio of a substance's density to the density of a reference material, usually water at 4°C for liquids/solids and air for gases, telling you how much denser or lighter a substance is compared to the reference. It's a dimensionless number (no units), where SG > 1 means the substance sinks (denser than water) and SG < 1 means it floats (lighter). It's used in industries to check purity, identify materials, and determine buoyancy.

Specific gravity tells you whether something is floating or sinking in water. A specific gravity below 1 means that the sample is less dense (lighter) than water and will, therefore, float. For example, an oil with a specific gravity of 0.825 will float on water.

Summary

Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass divided by volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nearly always measured with respect to water at its densest (at 4 °C or 39.2 °F); for gases, the reference is air at room temperature (20 °C or 68 °F). The term "relative density" (abbreviated r.d. or RD) is preferred in SI, whereas the term "specific gravity" is gradually being abandoned.

If a substance's relative density is less than 1 then it is less dense than the reference; if greater than 1 then it is denser than the reference. If the relative density is exactly 1 then the densities are equal; that is, equal volumes of the two substances have the same mass. If the reference material is water, then a substance with a relative density (or specific gravity) less than 1 will float in water. For example, an ice cube, with a relative density of about 0.91, will float. A substance with a relative density greater than 1 will sink.

Temperature and pressure must be specified for both the sample and the reference. Pressure is nearly always 1 atm (101.325 kPa). Where it is not, it is more usual to specify the density directly. For specific gravity, the reference temperature for water is often 4 °C (39.2 °F) because it's the point where water is densest (1 g/cc), but 15 °C (59 °F), 15.6 °C (60 °F), or 20 °C (68 °F) are also common standards, depending on the industry (like brewing or petroleum). In British brewing practice, the specific gravity, as specified above, is multiplied by 1000. Specific gravity is commonly used in industry as a simple means of obtaining information about the concentration of solutions of various materials such as brines, must weight (syrups, juices, honeys, brewers wort, must, etc.) and acids.

Details

Specific gravity, also known as relative density, measures the density of a substance compared to the density of water.

Specific gravity is related to density, as both are physical properties used to determine how "dense" a particular material is. This material can be a gas, liquid, or solid.

Specific gravity and density are used to identify a material, determine the concentration of a liquid solution e.g., alcohol or sugar in a drink), or test whether a product is within specifications.

1. What Are Density and Specific Gravity?

The density of a sample is defined as its mass divided by its volume.

Specific gravity, also known as relative density, is used to describe the density of a substance compared to the density of water. To calculate specific gravity, divide the sample's density by the density of water.

2. What Is the Difference Between Specific Gravity and Density?

The main difference between specific gravity and density is that specific gravity is dimensionless, meaning it has no units, while density has a unit g/cc.

Specific gravity tells you whether something is floating or sinking in water. A specific gravity below 1 means that the sample is less dense (lighter) than water and will, therefore, float. For example, an oil with a specific gravity of 0.825 will float on water.

3. How to Convert Specific Gravity to Density?

Density of the Substance = Specific Gravity of the Substance x Density of Water.

4. How Does the Temperature of Samples Affect the Specific Gravity and Density?

The temperature of a sample affects both the density and the specific gravity. The higher the temperature, the higher the volume and the lower the density. If the temperature increases, the volume increases, and the density decreases. However, the mass of the substance does not change with temperature.

The most notable exception to this rule is liquid water, which reaches its maximum density at 3.98 ºC; above this point, the volume of water increases, and it becomes less dense. The opposite is true when water is cooled.

Since specific gravity is the density of the sample divided by the density of water, both densities will decrease with increasing temperature, but not by the same magnitude. The effect of the temperature will usually be slightly less important for specific gravity than for density.

5. Which Instruments Are Used to Measure Specific Gravity and Density?

There are different types of instruments to measure both specific gravity and density:

Hydrometer

A hydrometer is a cost-effective instrument used to determine the specific gravity/density of liquids. Made of blown glass, it consists of a bulbous bottom weighted with lead or steel shot and a long, narrow stem with a scale. The hydrometer is immersed into the sample liquid until it floats. The density reading is taken by looking at the scale, where the level of the sample liquid aligns with a marking on the hydrometer scale. Most hydrometers measure the specific gravity of samples: in simple terms, a hydrometer tells the user if a liquid is denser or less dense than water. It will float higher in a liquid with a greater specific gravity, such as water with sugar dissolved, compared to one with a lower specific gravity, such as pure water or alcohol.

When using a hydrometer, the user has two options:

a) Use the hydrometer at its calibration temperature (usually 16 °C or 20 °C). Depending on the sample volume, it can take some time for the sample to reach this temperature.
b) Simply record the measurement value at the surrounding temperature. Both measurement and temperature values must be recorded. If needed, a correction factor can be applied later to obtain the temperature-corrected measurement value.

Pycnometer

Typically made of glass, a pycnometer is a flask of a pre-defined volume used to measure the specific gravity/density of a liquid. It can also determine the specific gravity/density of dispersions, solids, and even gases.

A thermometer is also required to measure the temperature. User training is required to guarantee accurate measurements with the pycnometer.

Portable digital density meter

Portable digital density meters are used to quickly and accurately determine the specific gravity/density of liquids. Determination of density or specific gravity using digital meters is based on two factors:

a) The oscillation, or vibration, of a U-shaped glass tube (U-tube).
b) The relationship between the liquid sample mass and the frequency of oscillation of the U-tube. Filling the U-tube with sample liquid affects its frequency of oscillation: due to factory adjustment with samples of known densities, this frequency of oscillation can be directly correlated with the density of any liquid sample with an accuracy of 0.001 g/{cm}^{3} or a specific gravity with an accuracy of 0.001. Handheld digital density meters measure the sample at ambient temperature. If a result is needed at a certain temperature, the digital density meter can apply a correction factor to the measured result to compensate the result to a defined temperature. Each measurement takes only a few seconds, allowing users to move on to the next sample quickly. The measured density can be automatically converted into other units and concentrations for specific applications, such as specific gravity, API, alcohol%, °Brix, etc.

Benchtop digital density meter

Benchtop digital density meters use the same technology as portable digital density meters, the oscillation of a U-shaped glass tube (U-tube). In addition, they feature a built-in Peltier temperature control, which brings the sample to the selected temperature (e.g., 20°C). The temperature control can range from 0 °C to 95 °C. These density meters can reach an accuracy of 0.000005 g/{m}^{3} for density, or 0.000005 for specific gravity.

Some benchtop digital density meters can be connected to sample automation solutions for single or multiple samples, which offer automated sampling, rinsing, and drying. These density meters can often be upgraded into a dedicated automated multi-parameter system combining density, refractive index, pH, color, conductivity, and more to save time, increase data quality, and prevent any alteration of samples between individual analyses.

One of the benefits of digital density meters using the U-shaped glass tube is the small volume of sample required (typically 1.5 mL), which allows for a faster temperature equilibrium of the sample.

Additional Information

Relative density is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material (i.e., water). It is usually measured at room temperature (20 Celsius degrees) and standard atmosphere (101.325kPa). It is unitless. You can often find it in the section 9 of a safety data sheet (SDS).

Regulatory Implications of Relative Density

Relative density is often used to calculate the volume or weight of samples needed for preparing a solution with a specified concentration. It also helps us understand the environmental distribution of insoluble substances (i.e, oil spill) in aquatic eco-system (on water surface or bottom sediment) if the substance is released to water.

Relative density test is not required for every chemical. Under REACH, the study does not need to be conducted if:

* the substance is only stable in solution in a particular solvent and the solution density is similar to that of the solvent. In such cases, an indication of whether the solution density is higher or lower than the solvent density is sufficient, or
* the substance is a gas. In this case, an estimation based on calculation shall be made from its molecular weight and the Ideal Gas Laws.

(REACH: REACH stands for Registration, Evaluation, Authorisation and Restriction of Chemicals, a comprehensive European Union regulation that governs the production and use of chemical substances to protect human health and the environment. It requires companies to register chemical substances, assess their risks, and manage them safely, placing the responsibility on industry to ensure chemical safety throughout the supply chain.)

Difference-Between-Density-and-Relative-Density1-768x483.jpg

Jai Ganesh · Dark Discussions at Cafe Infinity

Combine Quotes - II

1. A walk in nature is a perfect backdrop to combine exercise, prayer, and meditation while enhancing the benefit of these activities. - Chuck Norris

2. When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle. - Edmund Burke

3. I think no matter what you do you go through stages when you play. There was a number of times when I didn't do very well or was tired. It was too much to combine school and tennis altogether. Parents need to step in and say, take a little time off, do something fun. - Jana Novotna

4. I try to combine in my paintings cinematic feeling, emotional feeling, and sometimes actually writing on the page to combine all the different elements of communication. - Sylvester Stallone

5. When two elements combine and form more than one compound, the masses of one element that react with a fixed mass of the other are in the ratio of small whole numbers. - Humphry Davy

6. I've always loved to combine different scents to come up with my own unique thing. - Jennifer Aniston

7. In PhD, my topic was Stage Techniques in Sanskrit Drama - theory and practice. I wanted to combine my drama training with Sanskrit drama, which has a very rich history in literature. - Neena Gupta

8. I like making different recipes of my own, I love making food, I love learning about what food to combine with what other food. - Pooja Batra.

Jai Ganesh · Science HQ

Dispersion

Gist

Dispersion of light is the phenomenon where white light splits into its seven constituent colors (VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red) as it passes through a transparent medium, like a glass prism or water droplets. This occurs because different colors (wavelengths) of light travel at different speeds in the medium, causing them to bend, or refract, at slightly different angles, creating a spectrum.

In physics, dispersion is the phenomenon where a wave (like light, sound, or water waves) splits into its constituent frequencies or wavelengths, causing them to travel at different speeds, most famously seen as white light separating into a rainbow spectrum (VIBGYOR) when passing through a prism or water droplet. This happens because the refractive index or phase velocity of the medium changes with the wave's frequency, meaning different colors bend or travel at different rates, separating from the original beam.

Summary

Dispersion, in wave motion, is any phenomenon associated with the propagation of individual waves at velocities that depend on their wavelengths.

Ocean waves in deep water, for example, move at speeds proportional to the square root of their wavelengths; these speeds vary from a few meters per second for ripples to hundreds of kilometers per hour for tsunamis. (When ocean waves come closer to land in shallow water, the waves are nondispersive and move at a constant speed equal to the square root of the acceleration due to gravity times the depth of the water.)

In a vacuum, a wave of light has a defined speed, but in a transparent medium that speed varies inversely with the index of refraction (a measure of the angle by which the direction of a wave is changed as it moves from one medium into another). Any transparent medium—e.g., a glass prism—will cause an incident parallel beam of light to fan out according to the refractive index of the glass for each of the component wavelengths, or colors. This effect also causes rainbows, in which sunlight entering raindrops is spread out into its different wavelengths before it is reflected. This separation of light into colors is called angular dispersion or sometimes chromatic dispersion.

Chromatic dispersion is the change of index of refraction with wavelength. Generally the index decreases as wavelength increases, blue light traveling more slowly in the material than red light. Dispersion is the phenomenon which gives you the separation of colors in a prism. It also gives the generally undesirable chromatic aberration in lenses. Usually the dispersion of a material is characterized by measuring the index at the blue F line of hydrogen (486.1 nm), the yellow sodium D lines (589.3 nm), and the red hydrogen C line (656.3 nm).

Details

Dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency. Sometimes the term chromatic dispersion is used to refer to optics specifically, as opposed to wave propagation in general. A medium having this common property may be termed a dispersive medium.

Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, and in gravity waves (ocean waves). Within optics, dispersion is a property of telecommunication signals along transmission lines (such as microwaves in coaxial cable) or the pulses of light in optical fiber.

In optics, one important and familiar consequence of dispersion is the change in the angle of refraction of different colors of light, as seen in the spectrum produced by a dispersive prism and in chromatic aberration of lenses. Design of compound achromatic lenses, in which chromatic aberration is largely cancelled, uses a quantification of a glass's dispersion given by its Abbe number V, where lower Abbe numbers correspond to greater dispersion over the visible spectrum. In some applications such as telecommunications, the absolute phase of a wave is often not important but only the propagation of wave packets or "pulses"; in that case one is interested only in variations of group velocity with frequency, so-called group-velocity dispersion.

All common transmission media also vary in attenuation (normalized to transmission length) as a function of frequency, leading to attenuation distortion; this is not dispersion, although sometimes reflections at closely spaced impedance boundaries (e.g. crimped segments in a cable) can produce signal distortion which further aggravates inconsistent transit time as observed across signal bandwidth.

Examples

Dispersion causes a rainbow's spatial separation of a white light into components of different wavelengths (different colors). However, dispersion also has an effect in many other circumstances: for example, group-velocity dispersion causes pulses to spread in optical fibers, degrading signals over long distances; also, a cancellation between group-velocity dispersion and nonlinear effects leads to soliton waves.

Material and waveguide dispersion

Most often, chromatic dispersion refers to bulk material dispersion, that is, the change in refractive index with optical frequency. However, in a waveguide there is also the phenomenon of waveguide dispersion, in which case a wave's phase velocity in a structure depends on its frequency simply due to the structure's geometry. More generally, "waveguide" dispersion can occur for waves propagating through any inhomogeneous structure (e.g., a photonic crystal), whether or not the waves are confined to some region. In a waveguide, both types of dispersion will generally be present, although they are not strictly additive. For example, in fiber optics the material and waveguide dispersion can effectively cancel each other out to produce a zero-dispersion wavelength, important for fast fiber-optic communication.

Additional Information

A rainbow shining against a gloomy stormy sky is a sight that everyone loves. How does sunshine shining through pure raindrops produce the rainbow of colors observed? A transparent glass prism or a diamond uses the same method to break white light into colors. There are about six colors in a rainbow—red, black, yellow, green, blue, and violet; indigo is often identified as well.

Specific wavelengths of light are correlated with certain colors. Depending on the wavelength, we expect to see only one of the six colors as we absorb pure-wavelength light. Our eye's response to a combination of various wavelengths produces the thousands of other colors we can detect in other conditions. White light, in fact, is a combination of all visible wavelengths that are fairly uniform.

Because of the combination of wavelengths, sunlight, which is known bright, tends to be a little yellow, but it does include all visible wavelengths. The colors in rainbows are in the same order as the colors plotted against wavelength. This means the white light in a rainbow is distributed according to wavelength. This scattering of white light is known as Dispersion. More precisely, dispersion happens if a mechanism changes the direction of light in a wavelength-dependent way. Dispersion can occur with any form of wave and is often associated with wavelength-dependent processes.

What is a White Light?

Sometimes you have noticed that when you face towards the sun and see the sky you see the white light in the sky it is not really a white light it is a mixture of several colors. We can say that white light is the mixture of several colors having different wavelengths and frequency points on the same spot. We can also say that the complete blend of all the wavelengths of the spectrum is known as White Light.

The natural sources of white light are stars and the sun. The source of white light in the solar system is the sun. The artificial white light can be created with the help of LED and fluorescent light bulbs.

What is the Visible Light Spectrum?

Visible light waves are one of the significant forms of electromagnetic waves just like X-rays, infrared radiation, UV-rays, and microwaves. These waves can be visualized as the colors of the rainbow, with each color possessing a different wavelength. The wavelength of red is the longest, while that of violet is the smallest.

White light is formed when all the waves are seen together. As white light passes through the lens, it splits into the visible light spectrum's colors. The visible light spectrum is a portion of an electromagnetic spectrum which can we can see from our naked eyes. The human eye can only see light with a specific wavelength only, and it ranges between 380 and 740 nm. If we are considering the frequency then the range of frequency varies between 405 and 790 THz.

Dispersion

The phenomenon of splitting of visible light into its component colors is called dispersion. Dispersion of light is caused by the change of speed of light ray (resulting in angle of deviation) of each wavelength by a different amount.

The dispersion of a light wave by a prism is shown in the diagram. As white light is incident on a glass prism, the emergent light appears to be multicolored (violet, indigo, blue, green, yellow, orange and red). The light that bends the least is red, while the light that bends the most is violet. Dispersion is the process of light breaking into its constituent colors. The continuum of light is the pattern of color components in light.

When light falls on the surface it dispersed into several colors depending on the wavelength of the color or the frequency, as we know that frequency and wavelength are inversely proportional to each other. Each color has its own wavelength and frequency, so we see different colors for the same white light.

Causes of the Dispersion of Light

* The various degrees of refraction produced by different colors of light cause dispersion. In a vacuum, various colors of light travel at the same speed, but in a refracting medium, they travel at different speeds.
* Violet light travels at a much slower speed than red light. As a result, violet light has the highest refractive index of the medium, while red light has the lowest.
* As a result, violet light has the highest refractive index, while red light has the lowest refractive index (in the visible spectrum). As a consequence, violet-colored light refracts or bends the most, while red-colored light refracts the least.
* The dispersion of white light into its constituent colors as it emerges from a prism is caused by the disparity in the degree of bending of various colors of light.

Examples of Dispersion of Light

* Dispersion of white light through a prism: As shown in the figure, when white light falls on the prism a collection of seven colors found to come out from the prism due to the dispersion.
* Dispersion due to Oil on Road: Small amounts of oil are usually present on the road surface e.g. lubricating oil from automobiles, which give rise to bands of beautiful colors when it rains.
* Formation of Rainbow: A rainbow is considered to be one of the most amazing light displays ever seen on the planet. A rainbow is a multicolored arc formed by light striking water droplets. Rainbows are formed during rain by the absorption, refraction, and dispersion of light in water droplets. All of these phenomena provide a light spectrum in the sky, which is known as a rainbow.
* Dispersion in a Diamond: Diamond dispersion is where white light enters a diamond (or any dense object), separates into all the spectral colors of the rainbow, and bounces back to the viewer’s eyes in a wonderful display of colored light, also known as diamond fire.

Rainbow Formation

A Rainbow is formed of seven colors (VIBGYOR) Violet, Indigo, Blue, Green, Yellow, Orange, Red. When rain happens the drops of rain falling on the surface works like a prism and when sunlight falls on the drops of water the rays of the sun scatter into different colors and form a rainbow, and sometimes we may also see multiple rainbows. In this concept drops of water, acts likes a prism and create a rainbow. Drops of water are nothing but the spherical ball containing the water and having the refractive index of water (1.333) which makes the white light to dispersed and forming a beam of light of several called rainbow.

Therefore, the necessary conditions for the formation of the rainbow are: the presence of water droplets or raindrops and the position of Sun must be at the back side of the observer of rainbow.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10735. What does the term in Geography Crossroads mean?

#10736. What does the term in Geography Crust (geology) mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5931. What does the verb (used with object) infringe mean?

#5932. What does the adjective ingenious mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2562. What does the medical term Gustatory cortex mean?

Jai Ganesh · Jokes

Q: Why did the Oreo go to the dentist?
A: Because it lost its filling!
* * *
Q: What does the ginger bread man put on his bed?
A: A cookie sheet.
* * *
Q: What kind of keys do kids like to carry?
A: Cookies!
* * *
Q: What is a monkey's favorite cookie?
A: Chocolate chimp!
* * *
Q: What word backwards can predict the future?
A: Cookies (Seikooc as in psychic of you say it).
* * *

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9847.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6341.

Jai Ganesh · Exercises

Hi,

2698.

Jai Ganesh · This is Cool

Intelligence Quotient

Gist

An Intelligence Quotient (IQ) is a standardized, numerical score derived from tests designed to measure human cognitive abilities—such as reasoning, logic, memory, and problem-solving—relative to a peer group. Modern IQ scores are calculated using a normal distribution (bell curve) with a mean of 100 and a standard deviation of 15, meaning ~68% of the population scores between 85 and 115.

IQ (Intelligence Quotient) is a score from standardized tests measuring cognitive abilities, originally calculated by dividing a person's mental age (MA) by their chronological age (CA) and multiplying by 100: IQ = (MA / CA) × 100, though modern tests use statistical norms with a mean of 100, says Wikipedia. It assesses logic, memory, problem-solving, and pattern recognition, with average scores around 100, while scores below 70 suggest extremely low intelligence and above 129 indicate giftedness.

Summary

IQ, (from “intelligence quotient”), is a number used to express the relative intelligence of a person. It is one of many intelligence tests.

IQ was originally computed by taking the ratio of mental age to chronological (physical) age and multiplying by 100. Thus, if a 10-year-old child had a mental age of 12 (that is, performed on the test at the level of an average 12-year-old), the child was assigned an IQ of 12/10 × 100, or 120. If the 10-year-old had a mental age of 8, the child’s IQ would be 8/10 × 100, or 80. Based on this calculation, a score of 100—where the mental age equals the chronological age—would be average. Few tests continue to involve the computation of mental ages.

Details

An intelligence quotient (IQ) is a total score derived from a set of standardized tests or subtests designed to assess human intelligence. Originally, IQ was a score obtained by dividing a person's estimated mental age, obtained by administering an intelligence test, by the person's chronological age. The resulting fraction (quotient) was multiplied by 100 to obtain the IQ score. For modern IQ tests, the raw score is transformed to a normal distribution with mean 100 and standard deviation 15. This results in approximately two-thirds of the population scoring between IQ 85 and IQ 115 and about 2 percent each above 130 and below 70.

Scores from intelligence tests are estimates of intelligence. Unlike quantities such as distance and mass, a concrete measure of intelligence cannot be achieved given the abstract nature of the concept of "intelligence". IQ scores have been shown to be associated with factors such as nutrition, parental socioeconomic status, morbidity and mortality, parental social status, and perinatal environment. While the heritability of IQ has been studied for nearly a century, there is still debate over the significance of heritability estimates and the mechanisms of inheritance. The best estimates for heritability range from 40 to 60% of the variance between individuals in IQ being explained by genetics.

IQ scores were used for educational placement, assessment of intellectual ability, and evaluating job applicants. In research contexts, they have been studied as predictors of job performance and income. They are also used to study distributions of psychometric intelligence in populations and the correlations between it and other variables. Raw scores on IQ tests for many populations have been rising at an average rate of three IQ points per decade since the early 20th century, a phenomenon called the Flynn effect. Investigation of different patterns of increases in subtest scores can also inform research on human intelligence.

Historically, many proponents of IQ testing have been eugenicists who used pseudoscience to push later debunked views of racial hierarchy in order to justify segregation and oppose immigration. Such views have been rejected by a strong consensus of mainstream science, though fringe figures continue to promote them in pseudo-scholarship and popular culture.

Additional Information

Earlier this year, 11-year-old Kashmea Wahi of London, England scored 162 on an IQ test. That’s a perfect score. The results were published by Mensa, a group for highly intelligent people. Wahi is the youngest person ever to get a perfect score on that particular test.

Does her high score mean she will go on to do great things — like Stephen Hawking or Albert Einstein, two of the world’s greatest scientists? Maybe. But maybe not.

IQ, short for intelligence quotient, is a measure of a person’s reasoning ability. In short, it is supposed to gauge how well someone can use information and logic to answer questions or make predictions. IQ tests begin to assess this by measuring short- and long-term memory. They also measure how well people can solve puzzles and recall information they’ve heard — and how quickly.

Every student can learn, no matter how intelligent. But some students struggle in school because of a weakness in one specific area of intelligence. These students often benefit from special education programs. There, they get extra help in the areas where they’re struggling. IQ tests can help teachers figure out which students would benefit from such extra help.

IQ tests also can help identify students who would do well in fast-paced “gifted education” programs. Many colleges and universities also use exams similar to IQ tests to select students. And the U.S. government — including its military — uses IQ tests when choosing who to hire. These tests help predict which people would make good leaders, or be better at certain specific skills.

It’s tempting to read a lot into someone’s IQ score. Most non-experts think intelligence is the reason successful people do so well. Psychologists who study intelligence find this is only partly true. IQ tests can predict how well people will do in particular situations, such as thinking abstractly in science, engineering or art. Or leading teams of people. But there’s more to the story. Extraordinary achievement depends on many things. And those extra categories include ambition, persistence, opportunity, the ability to think clearly — even luck.

Intelligence matters. But not as much as you might think.

Measuring IQ

IQ tests have been around for more than a century. They were originally created in France to help identify students who needed extra help in school.

The U.S. government later used modified versions of these tests during World War I. Leaders in the armed forces knew that letting unqualified people into battle could be dangerous. So they used the tests to help find qualified candidates. The military continues to do that today. The Armed Forces Qualification Test is one of many different IQ tests in use.

IQ tests have many different purposes, notes Joel Schneider. He is a psychologist at Illinois State University in Normal. Some IQ tests have been designed to assess children at specific ages. Some are for adults. And some have been designed for people with particular disabilities.

But any of these tests will tend to work well only for people who share a similar cultural or social upbringing. “In the United States,” for instance, “a person who has no idea who George Washington was probably has lower-than-average intelligence,” Schneider says. “In Japan, not knowing who Washington was reveals very little about the person’s intelligence.”

Questions about important historical figures fall into the “knowledge” category of IQ tests. Knowledge-based questions test what a person knows about the world. For example, they might ask whether people know why it’s important to wash their hands before they eat.

IQ tests also ask harder questions to measure someone’s knowledge. What is abstract art? What does it mean to default on a loan? What is the difference between weather and climate? These types of questions test whether someone knows about things that are valued in their culture, Schneider explains.

Such knowledge-based questions measure what scientists call crystallized intelligence. But some categories of IQ tests don’t deal with knowledge at all.

Some deal with memory. Others measure what’s called fluid intelligence. That’s a person’s ability to use logic and reason to solve a problem. For example, test-takers might have to figure out what a shape would look like if it were rotated. Fluid intelligence is behind “aha” moments — times when you suddenly connect the dots to see the bigger picture.

Aki Nikolaidis is a neuroscientist, someone who studies structures in the brain. He works at the University of Illinois at Urbana-Champaign. And he wanted to know what parts of the brain are active during those “aha” episodes.

In a study published earlier this year, he and his team studied 71 adults. The researchers tested the volunteers’ fluid intelligence with a standard IQ test that had been designed for adults. At the same time, they mapped out which areas of test takers’ brains were working hardest. They did this using a brain scan called magnetic resonance spectroscopy, or MRS. It uses magnets to hunt for particular molecules of interest in the brain.

As brain cells work, they gobble up glucose, a simple sugar, and spit out the leftovers. MRS scans let researchers spy those leftovers. That told them which specific areas of people’s brains were working hard and breaking down more glucose.

People who scored higher on fluid intelligence tended to have more glucose leftovers in certain parts of their brains. These areas are on the left side of the brain and toward the front. They’re involved with planning movements, with spatial visualization and with reasoning. All are key aspects of problem solving.

“It’s important to understand how intelligence is related to brain structure and function,” says Nikolaidis. That, he adds, could help scientists develop better ways to boost fluid intelligence.

Personal intelligence

IQ tests “measure a set of skills that are important to society,” notes Scott Barry Kaufman. He’s a psychologist at the University of Pennsylvania in Philadelphia. But, he adds, such tests don’t tell the full story about someone’s potential. One reason: IQ tests favor people who can think on the spot. It’s a skill plenty of capable people lack.

It’s also something Kaufman appreciates as well as anyone.

As a boy, he needed extra time to process the words he heard. That slowed his learning. His school put him into special education classes, where he stayed until high school. Eventually, an observant teacher suggested he might do well in regular classes. He made the switch and, with hard work, indeed did well.

Kaufman now studies what he calls “personal intelligence.” It’s how people’s interests and natural abilities combine to help them work toward their goals. IQ is one such ability. Self-control is another. Both help people focus their attention when they need to, such as at school.

Psychologists lump together a person’s focused attention, self-control and problem-solving into a skill they call executive function. The brain cells behind executive function are known as the executive control network. This network turns on when someone is taking an IQ test. Many of the same brain areas are involved in fluid intelligence.

But personal intelligence is more than just executive function. It’s tied to personal goals. If people are working toward some goal, they’ll be interested and focused on what they are doing. They might daydream about a project even while not actively working on it. Although daydreaming may seem like a waste of time to outsiders, it can have major benefits for the person doing it.

When engaged in some task, such as learning, people want to keep at it, Kaufman explains. That means they will push forward, long after they might otherwise have been expected to give up. Engagement also lets a person switch between focused attention and mind wandering.

That daydreaming state can be an important part of intelligence. It is often while the mind is “wandering” that sudden insights or hunches emerge about how something works.

While daydreaming, a so-called default mode network within the brain kicks into action. Its nerve cells are active when the brain is at rest. For a long time, psychologists thought the default mode network was active only when the executive control network rested. In other words, you could not focus on an activity and daydream at the same time.

To see if that was really true, last year Kaufman teamed up with researchers at the University of North Carolina in Greensboro and at the University of Graz in Austria. They scanned the brains of volunteers using functional magnetic resonance imaging, or fMRI. This tool uses a strong magnetic field to record brain activity.

As they scanned the brains of 25 college students, the researchers asked the students to think of as many creative uses as they could for everyday objects. And as students were being as creative as possible, parts of both the default mode network and the executive control network lit up. The two systems weren’t at odds with each other. Rather, Kaufman suspects, the two networks work together to make creativity possible.

“Creativity seems to be a unique state of consciousness,” Kaufman now says. And he thinks it is essential for problem-solving.

Turning potential into achievement

Just being intelligent doesn’t mean someone will be successful. And just because someone is less intelligent doesn’t mean that person will fail. That’s one take-home message from the work of people like Angela Duckworth.

She works at the University of Pennsylvania in Philadelphia. Like many other psychologists, Duckworth wondered what makes one person more successful than another. In 2007, she interviewed people from all walks of life. She asked each what they thought made someone successful. Most people believed intelligence and talent were important. But smart people don’t always live up to their potential.

When Duckworth dug deeper, she found that the people who performed best — those who were promoted over and over, or made a lot of money — shared a trait independent of intelligence. They had what she now calls grit. Grit has two parts: passion and perseverance. Passion points to a lasting interest in something. People who persevere work through challenges to finish a project.

Duckworth developed a set of questions to assess passion and perseverance. She calls it her “grit scale.”

In one study of people 25 and older, she found that as people age, they become more likely to stick with a project. She also found that grit increases with education. People who had finished college scored higher on the grit scale than did people who quit before graduation. People who went to graduate school after college scored even higher.

She then did another study with college students. Duckworth wanted to see how intelligence and grit affected performance in school. So she compared scores on college-entrance exams (like the SAT), which estimate IQ, to school grades and someone’s score on the grit scale. Students with higher grades tended to have more grit. That’s not surprising. Getting good grades takes both smarts and hard work. But Duckworth also found that intelligence and grit don’t always go hand in hand. On average, students with higher exam scores tended to be less gritty than those who scored lower.

Students who perform best in the National Spelling Bee are those with grit. Their passion, drive, and persistance pay off and help them succeed against less “gritty” competitors.

But some people counter that this grit may not be all it’s cracked up to be. Among those people is Marcus Credé. He’s a psychologist at Iowa State University in Ames. He recently pooled the results of 88 studies on grit. Together, those studies involved nearly 67,000 people. And grit did not predict success, Credé found.

However, he thinks grit is very similar to conscientiousness. That someone’s ability to set goals, work toward them and think things through before acting. It’s a basic personality trait, Credé notes — not something that can be changed.

“Study habits and skills, test anxiety and class attendance are far more strongly related to performance than grit,” Credé concludes. “We can teach [students] how to study effectively. We can help them with their test anxiety,” he adds. “I’m not sure we can do that with grit.”

In the end, hard work can be just as important to success as IQ. “It’s okay to struggle and go through setbacks,” Kaufman says. It might not be easy. But over the long haul, toughing it out can lead to great accomplishments.

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Jai Ganesh · This is Cool

Diode

Gist

A diode is a two-terminal semiconductor device that acts as a one-way valve for electricity, allowing current to flow easily in one direction (forward-biased) while restricting it in the opposite direction (reverse-biased). Primarily used to convert alternating current (AC) to direct current (DC), they are essential for circuit protection, rectification, and voltage regulation.

A diode is a two-terminal semiconductor device acting as a one-way electrical valve, allowing current to flow easily in one direction (forward-biased) but blocking it in the reverse direction, making it crucial for power conversion (AC to DC), overvoltage protection (Zener diodes), signal demodulation (radios), light emission (LEDs), and building digital logic gates in computers. They are fundamental in electronics, found in everything from chargers to solar panels, by controlling current flow and protecting circuits.

Summary

A diode is a two-terminal electronic component that conducts electric current primarily in one direction (asymmetric conductance). It has low (ideally zero) resistance in one direction and high (ideally infinite) resistance in the other.

A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. It has an exponential current–voltage characteristic. Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other semiconducting materials such as gallium math and germanium are also used.

The obsolete thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from the cathode to the plate.

Among many uses, diodes are found in rectifiers to convert alternating current (AC) power to direct current (DC), demodulation in radio receivers, and can even be used for logic or as temperature sensors. A common variant of a diode is a light-emitting diode, which is used as electric lighting and status indicators on electronic devices.

Details

A diode is an electrical component that allows the flow of current in only one direction. In circuit diagrams, a diode is represented by a triangle with a line across one vertex.

The most common type of diode uses a p-n junction. In this type of diode, one material (n) in which electrons are charge carriers abuts a second material (p) in which holes (places depleted of electrons that act as positively charged particles) act as charge carriers. At their interface, a depletion region is formed across which electrons diffuse to fill holes in the p-side. This stops the further flow of electrons. When this junction is forward biased (that is, a positive voltage is applied to the p-side), electrons can easily move across the junction to fill the holes, and a current flows through the diode. When the junction is reverse biased (that is, a negative voltage is applied to the p-side), the depletion region widens and electrons cannot easily move across. The current remains very small until a certain voltage (the breakdown voltage) is reached and the current suddenly increases.

Light-emitting diodes (LEDs) are p-n junctions that emit light when a current flows through them. Several p-n junction diodes can be connected in series to make a rectifier (an electrical component that converts alternating current to direct current). Zener diodes have a well-defined breakdown voltage, so that current flows in the reverse direction at that voltage and a constant voltage can be maintained despite fluctuations in voltage or current. In varactor (or varicap) diodes, varying the bias voltage causes a variation in the diode’s capacitance; these diodes have many applications for signal transmission and are used throughout the radio and television industries. (For more detail about these and other types of diodes, see semiconductor device.)

Early diodes were vacuum tubes, an evacuated glass or metal electron tube containing two electrodes—a negatively charged cathode and a positively charged anode. These were used as rectifiers and as detectors in electronic circuits such as radio and television receivers. When a positive voltage is applied to the anode (or plate), electrons emitted from the heated cathode flow to the plate and return to the cathode through an external power supply. If a negative voltage is applied to the plate, electrons cannot escape from the cathode, and no plate current flows. Thus, a diode permits electrons to flow from cathode to plate but not from plate to cathode. If an alternating voltage is applied to the plate, current flows only during the time when the plate is positive. The alternating voltage is said to be rectified, or converted to direct current.

Additional Information

A diode is a semiconductor device, typically made of silicon, that essentially acts as a one-way switch for current. It allows current to flow easily in one direction but severely restricts current from flowing in the opposite direction.

Diodes are also known as rectifiers because they change alternating current (AC) into pulsating direct current (DC). Diodes are rated according to their type, voltage, and current capacity.

What Does a Diode Do?

Diodes have polarity, determined by an anode (positive lead) and cathode (negative lead). Most diodes allow current to flow only when positive voltage is applied to the anode.

When a diode allows current flow, it is forward-biased. When a diode is reverse-biased, it acts as an insulator and does not permit current to flow.

Strange but true: The diode symbol's arrow points against the direction of electron flow. The reason is that engineers conceived the symbol, and their schematics show current flowing from the positive (+) side of the voltage source to the negative (-). It's the same convention used for semiconductor symbols that include arrows — the arrow points in the permitted direction of "conventional" flow, and against the permitted direction of electron flow.

Types of Diodes

Different diode types all perform key functions in an electrical system. Here are some of the most important types of diodes.

* Rectifier Diodes: A rectifier diode converts AC into DC. Direct current flows in one consistent direction, making it easier to control.
* Zener Diodes: Zener diodes are designed to protect electrical systems from overvoltage. They conduct current in reverse whenever the cathode reaches a predetermined threshold voltage.
* Light Emitting Diodes: A light-emitting diode (LED) emits light when forward-biased current flows through it. LEDs are widely used in displays and indicators.
* Schottky Diodes: Schottky diodes, also known as barrier diodes or hot-carrier diodes, are often used in high-speed applications because of their fast-switching capabilities and their low forward voltage drop.
* Photodiodes: Photodiodes produce electrical currents when they absorb photons. They are widely used in sensors and in solar cells.

Diode Ratings and Testing

Every diode has a current and voltage rating, determined by factors like materials and design. Those ratings represent the maximum levels of voltage and currency the diode can tolerate.

Exceeding currency and voltage levels can cause permanent damage to the diode or to the whole circuit. High voltage levels may also cause the diode to short circuit and either allow current to flow in both directions or halt current from flowing in either direction.

Proper diode function can be tested with a digital multimeter (DMM).

Testing Diodes with a Digital Multimeter

There are two methods of testing diodes using a digital multimeter: diode test mode and resistance mode. Diode test mode is by far the more effective means of testing. Resistance testing is less reliable and should only be used if the multimeter does not have a diode test mode.

A digital multimeter's diode test produces a small voltage between the test leads, enough to forward-bias a diode junction. A good forward-bias diode displays a voltage drop from 0.5 to 0.8 volts (for most silicon diodes). The meter will display ‘OL’ when a good diode is reverse-biased. OL will indicate the diode is functioning as an open switch.

The forward-biased resistance of a good diode should range from 1000 ohms to 10 Mohms. Thereverse-biased resistance on a good diode, will read OL The diode is bad if readings are the same in both directions.

Applications of Diodes

* Power Conversion: Rectifiers convert AC signal into pulsing DC signal, making it easier to control the flow of power.
* Signal Demodulation: Demodulation diodes are a critical part of radio receivers. The diodes retrieve the original message sent through the airwaves for transmission.
* Overvoltage Protection: Zener diodes are used to protect circuits from unsafe voltage levels. They are also used to protect supply lines and power supply control lines.
* Logic Gates: Diodes play a crucial role in modern computing and digital technology. They make it possible to reinforce binary systems through gates that perform simple logic functions, like and/or/not.

Final Thoughts

Though small and simple, the diode is an essential part of modern electrical systems. By controlling the flow and direction of current, diodes enable countless applications of modern electronics.

Fortunately, tools like digital multimeters make it easy to measure diode health and determine when it’s time to replace diodes. This allows technicians to keep circuits in good running order, powering the electrical systems we all rely on.

Jai Ganesh · Dark Discussions at Cafe Infinity

2426) Pavel Cherenkov

Gist:

Work

In certain media the speed of light is lower than in a vacuum and particles can travel faster than light. One result of this was discovered in 1934 by Pavel Cherenkov, when he saw a bluish light around a radioactive preparation placed in water. Igor Tamm and Ilya Frank explained the phenomenon in 1937. On their way through a medium, charged particles disturb electrons in the medium. When these resume their position, they emit light. Normally this does not produce any light that can be observed, but if the particle moves faster than light, a kind of backwash of light appears.

Summary

Pavel Alekseyevich Cherenkov (born July 15 [July 28, New Style], 1904, Novaya Chigla, Russia—died Jan. 6, 1990, U.S.S.R.) was a Soviet physicist who shared the 1958 Nobel Prize for Physics with fellow Soviet scientists Igor Y. Tamm and Ilya M. Frank for the discovery and theoretical interpretation of the phenomenon of Cherenkov radiation.

A peasant’s son, Cherenkov graduated from Voronezh State University in 1928; he later became a research student at the P.N. Lebedev Physical Institute. In 1934, working on his dissertation under the guidance of and in collaboration with Sergei Ivanovich Vavilov, he observed that electrons produce a faint blue glow when passing through a transparent liquid at high velocity. This Cherenkov radiation, which was correctly explained by Tamm and Frank in 1937, led to the development of the Cherenkov counter, or Cherenkov detector, that later was used extensively in experimental nuclear and particle physics. Cherenkov continued to do research in nuclear and cosmic-ray physics at the P.N. Lebedev Physical Institute. Cherenkov was elected to the U.S.S.R. Academy of Sciences as a corresponding (1964) and subsequently full (1970) member.

Details

Pavel Alekseyevich Cherenkov (28 July 1904 – 6 January 1990) was a Soviet physicist who shared the 1958 Nobel Prize in Physics with Ilya Frank and Igor Tamm "for the discovery and interpretation of the Cherenkov effect".

Biography

Cherenkov was born into a Russian family on July 28, 1904, to Alexey Cherenkov and Mariya Cherenkova in the small village of Novaya Chigla. This town is in present-day Voronezh Oblast, Russia.

In 1928, he graduated from the Department of Physics and Mathematics of Voronezh State University. In 1930, he took a post as a senior researcher in the Lebedev Physical Institute. That same year he married Maria Putintseva, daughter of A.M. Putintsev, a Professor of Russian Literature. They had a son, Alexey, and a daughter, Yelena.

Cherenkov was promoted to section leader, and in 1940 was awarded the degree of Doctor of Physico-Mathematical Sciences. In 1953, he was confirmed as Professor of Experimental Physics. Starting in 1959, he headed the institute's photo-meson processes laboratory. He remained a professor for fourteen years. In 1970, he became Academician of the USSR Academy of Sciences.

Cherenkov died in Moscow on 6 January 1990 and was buried in Novodevichy Cemetery.

Discoveries in physics

In 1934, while working under S. I. Vavilov, Cherenkov observed the emission of blue light from a bottle of water subjected to radioactive bombardment. This phenomenon, associated with charged subatomic particles moving at velocities greater than the phase velocity of light, proved to be of great importance in subsequent experimental work in nuclear physics, and for the study of cosmic rays. Eponymously, it was dubbed the Cherenkov effect, as was the Cherenkov detector, which has become a standard piece of equipment in particle-physics research for observing the existence and velocity of high-speed particles. Such a device was installed in Sputnik 3.

Pavel Cherenkov also shared in the development and construction of electron accelerators and in the investigation of photo-nuclear and photo-meson reactions.

Awards and honours

Cherenkov was awarded two Stalin Prizes, the first in 1946, sharing the honor with Vavilov, Frank and Tamm, and another in 1952. He was also awarded the USSR State Prize in 1977. In 1958, he was awarded the Nobel Prize in Physics for the discovery of the Cherenkov effect. He was also awarded the Soviet Union's Hero of Socialist Labour title in 1984. Cherenkov was a member of the Communist Party of the Soviet Union since 1946.

Jai Ganesh · This is Cool

2488) Mass

Gist

In physics, mass is the fundamental property of matter that quantifies the amount of "stuff" in an object and its resistance to acceleration (inertia), measured in kilograms (kg). It's a scalar quantity, meaning it has magnitude but no direction, and remains constant regardless of location, unlike weight, which is a force dependent on gravity. Mass determines how much force is needed to change an object's motion.

The simple definition of mass is the quantity of matter within a given object. Mass is determined by the atomic and molecular makeups of objects. All objects are made up of protons, neutrons, and electrons, and each of these has different makeups and masses.

Summary

Mass is an intrinsic property of a body. In modern physics, it is generally defined as the strength of an object's gravitational attraction to other bodies - as measured by an observer moving along at the same speed.

It was traditionally believed to be related to the quantity of matter in a body, until the discovery of the atom and particle physics. It was found that different atoms and different elementary particles, theoretically with the same amount of matter, have nonetheless different masses. Mass in modern physics has multiple definitions which are conceptually distinct, but physically equivalent.

Mass can be experimentally defined as a measure of the body's inertia, meaning the resistance to acceleration (change of velocity) when a net force is applied.

The SI base unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.

In the Standard Model of physics, the mass of elementary particles is believed to be a result of their coupling with the Higgs boson in what is known as the Brout–Englert–Higgs mechanism.

Details

Mass, in physics, is a quantitative measure of inertia, a fundamental property of all matter. It is, in effect, the resistance that a body of matter offers to a change in its speed or position upon the application of a force. The greater the mass of a body, the smaller the change produced by an applied force. The unit of mass in the International System of Units (SI) is the kilogram, which is defined in terms of Planck’s constant, which is defined as equal to 6.62607015 × {10}^{-34} joule second. One joule is equal to one kilogram times metre squared per second squared. With the second and the metre already defined in terms of other physical constants, the kilogram is determined by accurate measurements of Planck’s constant. (Until 2019 the kilogram was defined by a platinum-iridium cylinder called the International Prototype Kilogram kept at the International Bureau of Weights and Measures in Sèvres, France.) In the English system of measurement, the unit of mass is the slug, a mass whose weight at sea level is 32.17 pounds.

Weight, though related to mass, nonetheless differs from the latter. Weight essentially constitutes the force exerted on matter by the gravitational attraction of Earth, and so it varies slightly from place to place. In contrast, mass remains constant regardless of its location under ordinary circumstances. A satellite launched into space, for example, weighs increasingly less the farther it travels away from Earth. Its mass, however, stays the same.

According to the principle of conservation of mass, the mass of an object or collection of objects never changes, no matter how the constituent parts rearrange themselves. If a body split into pieces, the mass divides with the pieces, so that the sum of the masses of the individual pieces is equal to the original mass. Or, if particles are joined together, the mass of the composite is equal to the sum of the masses of the constituent particles. However, this principle is not always correct.

With the advent of the special theory of relativity by Einstein in 1905, the notion of mass underwent a radical revision. Mass lost its absoluteness. The mass of an object was seen to be equivalent to energy, to be interconvertible with energy, and to increase significantly at exceedingly high speeds near that of light (about 3 × {10}^{8} metres per second, or 186,000 miles per second). The total energy of an object was understood to comprise its rest mass as well as its increase of mass caused by high speed. The rest mass of an atomic nucleus was discovered to be measurably smaller than the sum of the rest masses of its constituent neutrons and protons. Mass was no longer considered constant, or unchangeable. In both chemical and nuclear reactions, some conversion between mass and energy occurs, so that the products generally have smaller or greater mass than the reactants. The difference in mass is so slight for ordinary chemical reactions that mass conservation may be invoked as a practical principle for predicting the mass of products. Mass conservation is invalid, however, for the behaviour of masses actively involved in nuclear reactors, in particle accelerators, and in the thermonuclear reactions in the Sun and stars. The new conservation principle is the conservation of mass-energy.

Additional Information

Key takeaways

* Mass is the quantity of matter that makes up a given object
* Mass and weight are not the same thing. Mass deals with matter. Weight deals with the gravitational pull the Earth has on an object.
* The formula for calculating mass is Mass = Density x Volume. You can also find an object’s inertial and gravitational mass.

Mass definition

Mass is everywhere you look. Everything that is made up of something has mass. Even the oxygen we breathe has mass!

Understanding mass gives you a greater understanding of the way the world around you works. The screen you’re reading off of right now has mass! The keyboard you type with has mass! The food you eat, the bed you sleep on, and the bus you ride to school are all made of mass.

That’s because mass is made up of atoms, and everything we see contains atoms.

Mass is all around you, but what is mass exactly?

Mass definition

The simple definition of mass is the quantity of matter within a given object.

Mass is determined by the atomic and molecular makeups of objects. All objects are made up of protons, neutrons, and electrons, and each of these has different makeups and masses.

Units of mass

In 1875, scientists at the International Metric Convention created the International Prototype Kilogram which would, from then on, be used as the basis for mass measurement. The prototype kilogram was used to standardise one kilogram for every country in the world and therefore standardise the units of mass.

Part of the metric system, the kilogram, kg, then became what is called an SI unit of mass, or a part of the International System of Units.

Even though the physical prototype kilogram was replaced with a more practical definition in 2019, the kg and the SI unit are still used to measure mass today.

The mass unit of measure is the kilograms and multiples or fractions of the kilogram. The chart of mass units below demonstrates the most common units used to measure mass.

Mass vs weight

Mass and weight often get confused because in many cases, they both deal with the concept of heaviness and lightness. However, the two are very different!

First, let’s define mass again.

According to the mass definition, mass is a measurement of the quantity of matter. Mass is measured in grams and related units.

Weight is the measurement of the Earth’s gravitational pull on an object. Weight is measured in ounces, pounds, and tons.

Weight is the combination of mass and gravity: Weight = Mass x Gravity

Your weight depends on the gravitational pull of the Earth. If you were standing on Mars, your weight would depend on the gravitational pull of Mars, and therefore, you would have a different weight. Your mass, on the other hand, does not depend on gravity and will not change no matter where in the universe you are.

On Earth, it just so happens that weight and mass tend to be very similar. This is why the two are so easily confused with each other.

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Jai Ganesh · Dark Discussions at Cafe Infinity

Combine Quotes - I

1. When you combine ignorance and leverage, you get some pretty interesting results. - Warren Buffett

2. I dream of the realization of the unity of Africa, whereby its leaders combine in their efforts to solve the problems of this continent. I dream of our vast deserts, of our forests, of all our great wildernesses. - Nelson Mandela

3. When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle. - Edmund Burke

4. I have done one thing that I think is a contribution: I helped Buddhist science and modern science combine. No other Buddhist has done that. Other lamas, I don't think they ever pay attention to modern science. Since my childhood, I have a keen interest. - Dalai Lama

5. I know of no single formula for success. But over the years I have observed that some attributes of leadership are universal and are often about finding ways of encouraging people to combine their efforts, their talents, their insights, their enthusiasm and their inspiration to work together. - Queen Elizabeth II

6. The attempt to combine wisdom and power has only rarely been successful and then only for a short while. - Albert Einstein

7. All the interests of my reason, speculative as well as practical, combine in the three following questions: 1. What can I know? 2. What ought I to do? 3. What may I hope? - Immanuel Kant

8. Invention is not enough. Tesla invented the electric power we use, but he struggled to get it out to people. You have to combine both things: invention and innovation focus, plus the company that can commercialize things and get them to people. - Larry Page.

Jai Ganesh · Science HQ

Refraction

Gist

Refraction is the bending of a wave—most commonly light—as it passes obliquely from one transparent medium to another, caused by a change in its speed. It occurs because light travels at different velocities in materials of different densities (e.g., passing from air into water). This phenomenon is essential for lenses, prisms, and human vision.

Refraction is the bending of a wave, like light, sound, or water waves, as it passes from one transparent medium (like air) to another (like water or glass) due to a change in its speed, causing a change in direction. This common phenomenon explains why a straw in a glass of water looks bent, and it's essential for lenses, glasses, cameras, and even the formation of rainbows.

Summary

Refraction, in physics, is the change in direction of a wave passing from one medium to another caused by its change in speed. For example, waves travel faster in deep water than in shallow. If an ocean wave approaches a beach obliquely, the part of the wave farther from the beach will move faster than the part closer in, and so the wave will swing around until it moves in a direction perpendicular to the shoreline. The speed of sound waves is greater in warm air than in cold. At night, air is cooled at the surface of a lake, and any sound that travels upward is refracted down by the higher layers of air that still remain warm. Thus, sounds, such as voices and music, can be heard much farther across water at night than in the daytime.

The electromagnetic waves constituting light are refracted when crossing the boundary from one transparent medium to another because of their change in speed. A straight stick appears bent when partly immersed in water and viewed at an angle to the surface other than 90°. A ray of light of one wavelength, or colour (different wavelengths appear as different colours to the human eye), in passing from air to glass is refracted, or bent, by an amount that depends on its speed in air and glass, the two speeds depending on the wavelength. A ray of sunlight is composed of many wavelengths that in combination appear to be colourless. Upon entering a glass prism, the different refractions of the various wavelengths spread them apart as in a rainbow.

Details

Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law.

The bending of refraction can be visualized in terms of Huygens' principle. As the speed of light is reduced in the slower medium, the wavelength is shortened proportionately. The frequency is unchanged; it is a characteristic of the source of the light and unaffected by medium changes.

The index of refraction is defined as the speed of light in vacuum divided by the speed of light in the medium.

Snell's Law relates the indices of refraction n of the two media to the directions of propagation in terms of the angles to the normal. Snell's law can be derived from Fermat's Principle or from the Fresnel Equations.

If the incident medium has the larger index of refraction, then the angle with the normal is increased by refraction. The larger index medium is commonly called the "internal" medium, since air with n=1 is usually the surrounding or "external" medium. You can calculate the condition for total internal reflection by setting the refracted angle = 90° and calculating the incident angle. Since you can't refract the light by more than 90°, all of it will reflect for angles of incidence greater than the angle which gives refraction at 90°.

$Refraction-and-Snells-law.png$

Additional Information

In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed.

Optical prisms and lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wavelength of light, and thus the angle of the refraction also varies correspondingly. This is called dispersion and allows prisms and raindrops in rainbows to divide white light into its constituent spectral colors.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10733. What does the term in Geography Creek mean?

#10734. What does the term in Geography Crevasse mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5929. What does the adjective homologous mean?

#5930. What does the noun homophone mean?

Jai Ganesh · Jai Ganesh's Puzzles

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#2561. What does the medical term Fragile X syndrome mean?

Jai Ganesh · Jokes

Q: What cookie makes you rich?
A: A fortune cookie!
* * *
Q: Why do girls scouts sell cookies?
A: They wanna make a sweet first impression.
* * *
Q: When should you take a cookie to the doctor?
A: When it feels crummy.
* * *
Q: What do the cookie and the computer have in common?
A: They both have chips.
* * *
Q: What is green and brown and crawls through the grass?
A: A Girl Scout who has lost her cookie.
* * *

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9846.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6340.

Jai Ganesh · Exercises

Hi,

2697.

Math Is Fun Forum

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