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#1 2013-11-16 22:54:17

niharika_kumar
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mirror- help me!

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.


friendship is tan 90°.

#2 2013-11-16 22:59:54

anonimnystefy
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Re: mirror- help me!

Do you have the picture?


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#3 2013-11-16 23:00:38

bobbym
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Re: mirror- help me!

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


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#4 2013-11-16 23:34:57

Agnishom
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Re: mirror- help me!

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.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Who are you to judge everything?' -Alokananda

#5 2013-11-17 03:28:14

niharika_kumar
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Re: mirror- help me!

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

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

post #77


friendship is tan 90°.

#6 2013-11-17 03:29:25

niharika_kumar
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Re: mirror- help me!

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


friendship is tan 90°.

#7 2013-11-17 03:30:59

bobbym
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Re: mirror- help me!

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.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#8 2013-11-17 03:36:14

Agnishom
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Re: mirror- help me!

http://www.mathisfunforum.com/showimage.php?pid=290049&filename=mirror.gif


'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'
'Who are you to judge everything?' -Alokananda

#9 2013-11-17 05:13:36

bobbym
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Re: mirror- help me!

Hi;

The formula says 30.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#10 2013-11-17 05:26:36

ShivamS
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Re: mirror- help me!

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


I have discovered a truly marvellous signature, which this margin is too narrow to contain. -Fermat
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world. -Archimedes
Young man, in mathematics you don't understand things. You just get used to them. - Neumann

#11 2013-11-17 07:44:50

Nehushtan
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Re: mirror- help me!

I got 35 instead but I don’t know where I went wrong. sad

EDIT: I got it now. I carelessly used sin instead of tan.

Last edited by Nehushtan (2013-11-17 16:39:26)


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#12 2013-11-17 10:44:06

bob bundy
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Re: mirror- help me!

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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#13 2013-11-19 15:29:24

niharika_kumar
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Re: mirror- help me!

thank you! smile


friendship is tan 90°.

#14 2013-11-20 08:13:56

ShivamS
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Re: mirror- help me!

Niharika, you are preparing for the JEE?


I have discovered a truly marvellous signature, which this margin is too narrow to contain. -Fermat
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world. -Archimedes
Young man, in mathematics you don't understand things. You just get used to them. - Neumann

#15 2013-11-21 03:59:23

niharika_kumar
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Re: mirror- help me!

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?


friendship is tan 90°.

#16 2013-11-21 04:16:54

Agnishom
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Re: mirror- help me!

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'
'Who are you to judge everything?' -Alokananda

#17 2013-11-21 15:33:19

niharika_kumar
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Re: mirror- help me!

yes (as far as I know).


friendship is tan 90°.

#18 2014-03-10 03:08:26

ShivamS
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Re: mirror- help me!

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.


I have discovered a truly marvellous signature, which this margin is too narrow to contain. -Fermat
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world. -Archimedes
Young man, in mathematics you don't understand things. You just get used to them. - Neumann

#19 2014-03-10 19:06:56

niharika_kumar
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Re: mirror- help me!

wow, that's really great.

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


friendship is tan 90°.

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