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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,060

pls help

Q. Two plane mirrors A and B are aligned parallel to each other as shown in fig.

A light is incident at an angle 30° at a point just inside one end of A .The plane of incidence coincides with the plane of figure.Find the maximum number of times the ray undergoes reflections before it emerges out.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 15,954

Do you have the picture?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,275

I thought you had figured out how to post a picture?

**In mathematics, you don't understand things. You just get used to them.**

**If it ain't broke, fix it until it is.** **Thinking is cheating.**

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Alternately you can upload the picture in a familiar site and post the image hotlink here

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,060

pls copy paste the following link for the fig.:-

http://www.mathisfunforum.com/viewtopic.php?pid=290049#p290049

post #77

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,060

i am still not able to find the upload option in this section.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,275

It is in post reply on the bottom, I can make a picture of it if you need it.

**In mathematics, you don't understand things. You just get used to them.**

**If it ain't broke, fix it until it is.** **Thinking is cheating.**

**Online**

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

'But our love is like the wind. I can't see it but I can feel it.' -A Walk to remember

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,275

Hi;

The formula says 30.

**In mathematics, you don't understand things. You just get used to them.**

**If it ain't broke, fix it until it is.** **Thinking is cheating.**

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,646

What a coincidence! This is the same question I encountered while taking the IIT JEE some years back. The answer is 30.

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,273

hi niharika_kumar

When the ray hits mirror B for the first time it has travelled in the right/left direction

This can happen until it has travelled 2root 3 in that direction. Say it happens n times then

But the ray has also hit A at the start so add one, but 'just' misses B at the end so take one off.

Hence the maximum number of reflections is 30.

Bob

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You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,060

thank you!

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,646

Niharika, you are preparing for the JEE?

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,060

JEE is my goal and its preparations are going in parallel, but now I am in class10 so my focus is more on boards.

Did you give JEE,if yes then how was it?

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What is JEE? Joint Entrance Examinations?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

'But our love is like the wind. I can't see it but I can feel it.' -A Walk to remember

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,060

yes (as far as I know).

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,646

niharika_kumar wrote:

JEE is my goal and its preparations are going in parallel, but now I am in class10 so my focus is more on boards.

Did you give JEE,if yes then how was it?

Just saw this post right now...

It wasn't extremely hard. I managed to crack the main and the advanced (AIR 52) but decided to go to MIT instead. For your preparation, try plancess.com (it gives tutorials by IIT JEE crackers AIR <100). Use NCERT books for all the subjects, but for physics go for HC Verma.

Good luck.

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,060

wow, that's really great.

thanks for your suggestion.will try that after my exams are over.

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