Q 9.31 Light incident normally on a plane mirror attached to a galvanometer coil retraces backwards as shown in Fig. 9.33. A current in the coil produces a deflection of 3.5o of the mirror. What is the displacement of the reflected spot of light on a screen placed 1.5 m away?



Answers (1)
P Pankaj Sanodiya


Angle of deflection \delta = 3.5^0

The distance of the screen from the mirror D=1.5m

The reflected rays will bet deflected by twice angle of deviation that is

 2\delta =3.5*2=7^0

Now from the figure, it can be seen that

tan2\delta =\frac{d}{1.5}

d=1.5*\tan2\delta = 2*\tan7=0.184m=18.4cm

Hence displacement of the reflected spot of the light is 18.4cm.