Question

Two verticle plane mirrors are inclined at an angle of 60 with each other. A ray of light travelling horizontally is reflected first from one mirror and the other. The resultant deviation is
1)60. 2) 120. 3)180 4)240

Answer 1

Answer:

Explanation:

a + b = 90o

=> b = 90 – a

Now,

b + 60 + c = 180

=> c = 180 – 60 – b = 120 – (90 – a) = 30 + a

Now,

d + c = 90

=> d = 90 – c = 90 – (30 + a) = 60 – a

Thus, in triangle PQR,

∟Q = 2a

And, ∟R = 2d = 2(60 – a) = 120 – 2a

So, angle ∟QPT is = ∟Q + ∟R = 120

Angle of deviation = reflex ∟QPT

= 360 – 120

= 2400