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 `/_theta = 3.5^@`, the reflected ray turns through
`/_2 theta = 7^@ = /_AOB`
`OA = d = 1.5 m`
Displacement, `AB = x = ?`
In `Delta AOB tan 2 theta = (x)/(d)`
`x = d tan 2 theta = 1.5 tan 7^@ = 1.5 xx 0.1228`
=`0.18 metre`.
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