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 $3.5^{\circ }$ of the mirror. The displacement of the reflected spot of light on a screen placed $1.0m$ away is

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

Answer 1

Answer: (C)

Angle of deflection is $\theta =3.5^{\circ }$, Distance,
between the screen and the mirror is $=2.0m$
The reflected rays get deflected by an amount twice the angle of deflection,
i.e., $2\theta =7.0^{\circ }$
$\therefore tan2\theta =\frac{d}{2}$
$\Rightarrow d=2\times tan{7}^{\circ }$
$=2\times 0.1227$
$=0.245m$
$=24.5cm$