Question

Light incident normally on a plane mirror attached to a galvanometer coil reflects backward as shown in figure. A current in the coil produces a deflection of 3.50 of 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

Answer: (C)

24.5 cm

Answer 2

: Angle of deflection is $\theta = 3.5 ^ { \circ }$ Distance, between the screen and the mirror is = $2.0$ m

The reflected rays get deflected by an amount twice the angle of deflection,

i.e., $2 \theta = 7.0 ^ { \circ } \therefore \tan 2 \theta = \frac { \mathrm { d } } { 2 }$

$\Rightarrow \mathrm { d } = 2 \times \tan 7 ^ { \circ } = 2 \times 0.1227$

$= 0.245 \mathrm {~m} = 24.5 \mathrm {~cm}$