Class 12 Physics
CBSE and UP Board
Ray Optics and Optical Instruments
Chapter-9 Exercise 9.37
NCERT Solutions for Class 12 Physics Chapter 9 Question-37
Light incident normally on a plane mirror attached to a galvanometer coil retraces backwards as shown in Figure. A current in the coil produces a deflection of 3.5° of the mirror. What is the displacement of the reflected spot of light on a screen placed 1.5 m away?
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Angle of deflection, 0 = 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., 20 = 7.0°
The displacement (d) of the reflected spot of light on the screen is given as:
tan 20 = d/1.5 => d = 1.5 x tan 7° = 0.184 m = 18.4 cm
Hence, the displacement of the reflected spot of light is 18.4 cm.