Question

Light incident normally on a plane mirror attached to a galvenometer coil reflects backward as shown in figure. A current in the coil produes a deflection of `3.5^(@)` if the mirror. The displacement of the reflected spot of light on a screen placed `1.0 m` away is

A. `27.5 m`
B. `48.9 cm`
C. `24.5 cm`
D. `12.2 m`

Answer 1

Correct Answer - C
Angle of deflection is `theta = 3.5^(@)`, Distance between the screen and the mirror is `= 2.0 m`
The reflected rays gets deflected by an amount twice the angle of deflection , i.e., `2theta = 7.0^(@) :. tan 2 theta = d/2`
`rArr d = 2 xx tan 7^(@)= 2 xx 0.1227 = 0.245 m = 24.5 cm`