Light incident normally on a plane mirror attached to a galvanometer coil retraces backwards a shown in Fig. 6(a). 14. A current in the coil produces a deflection of `3.5^(@)` in the mirror. What is the displacement of the reflected spot of light on a screen placed `1.5 m` away ?

Explanation

Given, distance between the screen the plane of mirror = 1.5 m
In the above given figure the ray gets deflected by twice the angle of rotation of the mirror.
Thus, from the figure
`(d)/(1.5)=tan 2 theta`
`(d)/(1.5)=tan7^(@)=0.1228`
`d=1.5xx0.1228`
`=0.1842m`.
`=18.42cm`