Light incident normally on a plane mirror attached to a galvanometer coil retraces backwards as shown in Fig. 9.36. A current in the coil produces a deflection of 3.50 of the mirror. What is the displacement of the reflected spot of light on a screen placed 1.5 m away?
Given:
Angle of deflection, θ = 3.5°
Distance of the screen from the mirror, D = 1.5 m
The reflected rays get deflected by an amount twice the angle of deflection i.e.,
2θ = 7.0°
The displacement (d) of the reflected spot of light on the screen is given as:
tan2θ = d/1.5
(Using trigonometric ratio)
d = 1.5 x tan7o
d= 0.184 m = 18.4 cm
Hence, the displacement of the reflected spot of light is 18.4 cm
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