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NCERT Class XII Chapter
Ray Optics and Optical Instruments
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Question : 37 of 38
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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?
Solution:  
If the mirror deflect by 3.5°, the reflected light deflect by 7°, deflection of the spot d can be calculated
tan 7° = d1.5\frac{d}{1.5}
d = 1.5 tan 7° = 1.5 [0.1228] m
or d = 0.1842 m = 18.42 cm.
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