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  4. Assertion A ray of light incident along the normal to the plane mirror retraces its path after reflection from the mirror. Reason A ray of light along the normal has angle of incidence as π / 2 and hence, it retraces its own path after reflection from mirror.

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Q. Assertion A ray of light incident along the normal to the plane mirror retraces its path after reflection from the mirror.
Reason A ray of light along the normal has angle of incidence as $\pi / 2$ and hence, it retraces its own path after reflection from mirror.

Ray Optics and Optical Instruments

Solution:

Angle of incidence $=$ Angle between incident ray and normal to the mirror $=0^{\circ}$
image
$\Rightarrow $ Angle of reflection $=0^{\circ} $ (from laws of reflection)
Hence, the reflected ray retraces its path along the normal at an angle $0^{\circ}$ with normal.