Hi,

M # 394. If the diameter of a circle is increased by 8%, then its area is increased by how many percent?

Hi,

#3045. What does the noun cul-de-sac mean?

#3046. What does the verb (used with object) culminate mean?

Hi,

#6651. Find the value of x.

Hi,

M # 393. Each side of a rectangular field is diminished by 40%. By how many percent is the area of the field diminished?

373) Pierre Janssen

Pierre Janssen, in full Pierre Jules César Janssen, also called Jules Janssen, (born February 22, 1824, Paris, France—died December 23, 1907, Meudon), French astronomer who in 1868 discovered the chemical element helium and how to observe solar prominences without an eclipse. His work was independent of that of the Englishman Sir Joseph Norman Lockyer, who made the same discoveries at about the same time.

Janssen was permanently lamed by an accident in early childhood. He initially worked as a bank clerk. He graduated from the University of Paris in 1852, and in 1865 he became professor of physics at the École Speciale d’Architecture in Paris. He was an enthusiastic observer of eclipses.

While observing a solar eclipse in Guntur, India, on August 18, 1868, Janssen noted that the spectral lines in the solar prominences were so bright that they should be easily observable in daylight. The next day he used his spectroscope to study the solar prominences. That enabled many more such observations to be made than previously, when such phenomena had been observable only for the few minutes’ duration of solar eclipses. During his observations he also noted a yellow spectral line near, but distinct from, the prominent lines of sodium. That line was from helium, which was not observed on Earth until 1895.

In 1870, when Paris was besieged during the Franco-German War, Janssen fled the surrounded city in a balloon so that he could reach the path of totality of a solar eclipse in Algeria. (His effort went for nothing, for the eclipse was obscured by clouds.) In 1873 he invented the “photographic revolver,” a device designed to take 180 images at the rate of one frame per second. The revolver was used by Janssen in Japan to observe the 1874 transit of Venus and is considered a precursor of the motion-picture camera. In 1876 he was appointed the first director of the Meudon Observatory, near Paris. In 1893, using observations from the meteorological observatory he had established on Mont Blanc, he proved that strong oxygen lines appearing in the solar spectrum were caused by oxygen in Earth’s atmosphere.

Janssen was the first to regularly use photographs to study the Sun, and in 1903 he published his great 'Atlas de photographies solaires', containing more than 6,000 solar pictures.

Hi,

#4191. In how many different ways can the letters of the word 'BELIEVE'  be arranged?

Hi tony123,

y=4÷4×(3+1) = 1x(3+1) = 1x4 = 4.

Hi,

#3043. What does the noun cuff link mean?

#3044. What does the noun cuisine mean?

Hi,

#6649. Find the value of x : 38% of 4500- 25% of x = 1640.

Hi,

M # 391. If the circumference of a circle is reduced by 50%, then its area will be reduced by how many percent?

372) Richard Feynman

Richard Feynman, in full Richard Phillips Feynman, (born May 11, 1918, New York, New York, U.S.—died February 15, 1988, Los Angeles, California), American theoretical physicist who was widely regarded as the most brilliant, influential, and iconoclastic figure in his field in the post-World War II era.

Feynman remade quantum electrodynamics—the theory of the interaction between light and matter—and thus altered the way science understands the nature of waves and particles. He was co-awarded the Nobel Prize for Physics in 1965 for this work, which tied together in an experimentally perfect package all the varied phenomena at work in light, radio, electricity, and magnetism. The other cowinners of the Nobel Prize, Julian S. Schwinger of the United States and Tomonaga Shin’ichirō of Japan, had independently created equivalent theories, but it was Feynman’s that proved the most original and far-reaching. The problem-solving tools that he invented—including pictorial representations of particle interactions known as Feynman diagrams—permeated many areas of theoretical physics in the second half of the 20th century.

Born in the Far Rockaway section of New York City, Feynman was the descendant of Russian and Polish Jews who had immigrated to the United States late in the 19th century. He studied physics at the Massachusetts Institute of Technology, where his undergraduate thesis (1939) proposed an original and enduring approach to calculating forces in molecules. Feynman received his doctorate at Princeton University in 1942. At Princeton, with his adviser, John Archibald Wheeler, he developed an approach to quantum mechanics governed by the principle of least action. This approach replaced the wave-oriented electromagnetic picture developed by James Clerk Maxwell with one based entirely on particle interactions mapped in space and time. In effect, Feynman’s method calculated the probabilities of all the possible paths a particle could take in going from one point to another.

During World War II Feynman was recruited to serve as a staff member of the U.S. atomic bomb project at Princeton University (1941–42) and then at the new secret laboratory at Los Alamos, New Mexico (1943–45). At Los Alamos he became the youngest group leader in the theoretical division of the Manhattan Project. With the head of that division, Hans Bethe, he devised the formula for predicting the energy yield of a nuclear explosive. Feynman also took charge of the project’s primitive computing effort, using a hybrid of new calculating machines and human workers to try to process the vast amounts of numerical computation required by the project. He observed the first detonation of an atomic bomb on July 16, 1945, near Alamogordo, New Mexico, and, though his initial reaction was euphoric, he later felt anxiety about the force he and his colleagues had helped unleash on the world.

At war’s end Feynman became an associate professor at Cornell University (1945–50) and returned to studying the fundamental issues of quantum electrodynamics. In the years that followed, his vision of particle interaction kept returning to the forefront of physics as scientists explored esoteric new domains at the subatomic level. In 1950 he became professor of theoretical physics at the California Institute of Technology (Caltech), where he remained the rest of his career.

Five particular achievements of Feynman stand out as crucial to the development of modern physics. First, and most important, is his work in correcting the inaccuracies of earlier formulations of quantum electrodynamics, the theory that explains the interactions between electromagnetic radiation (photons) and charged subatomic particles such as electrons and positrons (antielectrons). By 1948 Feynman completed this reconstruction of a large part of quantum mechanics and electrodynamics and resolved the meaningless results that the old quantum electrodynamic theory sometimes produced. Second, he introduced simple diagrams, now called Feynman diagrams, that are easily visualized graphic analogues of the complicated mathematical expressions needed to describe the behaviour of systems of interacting particles. This work greatly simplified some of the calculations used to observe and predict such interactions.

In the early 1950s Feynman provided a quantum-mechanical explanation for the Soviet physicist Lev D. Landau’s theory of superfluidity—i.e., the strange, frictionless behaviour of liquid helium at temperatures near absolute zero. In 1958 he and the American physicist Murray Gell-Mann devised a theory that accounted for most of the phenomena associated with the weak force, which is the force at work in radioactive decay. Their theory, which turns on the asymmetrical “handedness” of particle spin, proved particularly fruitful in modern particle physics. And finally, in 1968, while working with experimenters at the Stanford Linear Accelerator on the scattering of high-energy electrons by protons, Feynman invented a theory of “partons,” or hypothetical hard particles inside the nucleus of the atom, that helped lead to the modern understanding of quarks.

Feynman’s stature among physicists transcended the sum of even his sizable contributions to the field. His bold and colourful personality, unencumbered by false dignity or notions of excessive self-importance, seemed to announce: “Here is an unconventional mind.” He was a master calculator who could create a dramatic impression in a group of scientists by slashing through a difficult numerical problem. His purely intellectual reputation became a part of the scenery of modern science. Feynman diagrams, Feynman integrals, and Feynman rules joined Feynman stories in the everyday conversation of physicists. They would say of a promising young colleague, “He’s no Feynman, but….” His fellow physicists envied his flashes of inspiration and admired him for other qualities as well: a faith in nature’s simple truths, a skepticism about official wisdom, and an impatience with mediocrity.

Feynman’s lectures at Caltech evolved into the books 'Quantum Electrodynamics' (1961) and 'The Theory of Fundamental Processes' (1961). In 1961 he began reorganizing and teaching the introductory physics course at Caltech; the result, published as The Feynman Lectures on Physics, 3 vol. (1963–65), became a classic textbook. Feynman’s views on quantum mechanics, scientific method, the relations between science and religion, and the role of beauty and uncertainty in scientific knowledge are expressed in two models of science writing, again distilled from lectures: 'The Character of Physical Law' (1965) and 'QED: The Strange Theory of Light and Matter' (1985).

When Feynman died in 1988 after a long struggle with cancer, his reputation was still mainly confined to the scientific community; his was not a household name. Many Americans had seen him for the first time when, already ill, he served on the presidential commission that investigated the 1986 explosion of the space shuttle Challenger. He conducted a dramatic demonstration at a televised hearing, confronting an evasive NASA witness by dunking a piece of rubber seal in a glass of ice water to show how predictable the failure of the booster rocket’s rubber seal might have been on the freezing morning of Challenger’s launch. He added his own appendix to the commission’s report, emphasizing the space agency’s failures of risk management.

He achieved a growing popular fame after his death, in part because of two autobiographical collections of anecdotes published in the years around his passing, “Surely You’re Joking, Mr. Feynman!”: 'Adventures of a Curious Character' (1985) and “What Do You Care What Other People Think?”: 'Further Adventures of a Curious Character' (1988), which irritated some of his colleagues by emphasizing his bongo playing more than his technical accomplishments. Other popular books appeared posthumously, including 'Six Easy Pieces: Essentials of Physics Explained by Its Most Brilliant Teacher' (1994) and 'Six Not-So-Easy Pieces: Einstein’s Relativity, Symmetry, and Space-Time' (1997), and his life was celebrated in an opera (Feynman [2005], by Jack Vees), a graphic novel (Feynman [2011], by Jim Ottaviani and Leland Myrick), and a play (QED [2001], by Peter Parnell), the latter of which was commissioned by and starred Alan Alda.