Number of reflections undergone by light ray between 2 plane mirrors


by Amith2006
Tags: light, mirrors, number, plane, reflections, undergone
Amith2006
Amith2006 is offline
#1
Jun6-06, 01:59 PM
P: 424
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.
Attached Thumbnails
Opt 4.GIF  
Phys.Org News Partner Science news on Phys.org
Review: With Galaxy S5, Samsung proves less can be more
Making graphene in your kitchen
Study casts doubt on climate benefit of biofuels from corn residue
Doc Al
Doc Al is offline
#2
Jun6-06, 02:10 PM
Mentor
Doc Al's Avatar
P: 40,889
Your answer and method make sense to me; the book's answer does not.
Hootenanny
Hootenanny is offline
#3
Jun6-06, 02:13 PM
Emeritus
Sci Advisor
PF Gold
Hootenanny's Avatar
P: 9,789
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
Amith2006 is offline
#4
Jun6-06, 04:46 PM
P: 424

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.


Register to reply

Related Discussions
Nearsightedness and Plane Mirrors Introductory Physics Homework 2
Mirrors and reflections General Physics 7
Number of images formed by 3 mutually perpendicular plane mirrors Introductory Physics Homework 1
Decrease in intensity of light on undergoing successive reflections Introductory Physics Homework 1
unusual light reflections General Discussion 1