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 3.5 of the mirror. The displacement of the reflected spot of light on a screen placed 1.0 m away is

• A. $27.5m$
• B. $48.9cm$
• C. $24.5cm$
• D. $12.2m$

Answer 1

Answer: (C)

$24.5cm$

Angle of deflection is $\theta ={3.5}^o,$ Distance, between the screen and the mirror is = 2.0 mThe reflected rays get deflected by an amount twice the angle of deflection, i.e., $2\theta ={7.0}^o\therefore tan2\theta =\frac{d}{2}$
$\Rightarrow d=2\times tan{7}^o$

$=2\times 0.1227=0.245m$

$=24.5cm$