Question

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 ?

Answer 1

In Fig. when mirror is turned from position `M_(1)` to position `M_(2)` through `angletheta = 3.5^(@)`,
`angle2theta = 7^(@) = angleAOB`
`OA = d = 1.5 m`
Displacement. `AB = x = ?`

In `DeltaAOB = tan2theta = (x)/(d)`
`x = d tan 2theta = 1.5 tan 7^(@) = 1.5 xx 0.1228 = 0.18 metre`.