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Number of reflections undergone by light ray between 2 plane mirrors

by Amith2006
Tags: light, mirrors, number, plane, reflections, undergone
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Amith2006
#1
Jun6-06, 01:59 PM
P: 423
Sir,
Two plane mirrors M1 and M2 have a length of 2 meters each and are 10 cm apart. A ray of light is incident on one end of mirror M2 at an angle of 30 degrees. What is the number of reflections light undergoes before reaching the other end?
I solved it in the following way:
In each reflection the distance moved = 10 x tan(30)
= 5.77 cm
Therefore the number of reflections before it reaches
the other end = 200/5.77
= 34
But the answer given in my book is 170. Please help.
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Doc Al
#2
Jun6-06, 02:10 PM
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Your answer and method make sense to me; the book's answer does not.
Hootenanny
#3
Jun6-06, 02:13 PM
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Quote Quote by Doc Al
Your answer and method make sense to me; the book's answer does not.
I would also agree with you here. I obtained answer identical to yours Amith (34.64...) which rounds to 34 reflections. It seems your 'textbook' is making a significant number of errors. If you don't mind me asking what text are you reading from?

Amith2006
#4
Jun6-06, 04:46 PM
P: 423
Number of reflections undergone by light ray between 2 plane mirrors

Sir,
I kindly request you all to tolerate the erroneous questions of my book. There are about 150 questions in each unit out of which say about 7 to 8 questions have wrong answers. That is why I am still using it. I hope to get it corrected with your help.Thanks for your guidance.


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