Question

What happens when you throw a ray of light on the mirror along the normal?
A. The ray that comes after reflection makes ${60}^{\circ }$ with the mirror.
B. The incident ray did not come back.
C. The incident ray retraces its path.
D. None of the above

Answer 1

Hint: The natural phenomenon that happens when a ray of light strikes a surface is known as the reflection of light. The light when striking a rough surface reflects with various angles, but when it strikes a smooth surface the angle through which it reflects is the same as the angle with which it strikes the smooth surface. The mirror is a smooth surface.

Complete answer:
Reflection is defined as the natural phenomenon which refers to the bouncing back of a light ray when it strikes a surface. When the ray strikes a mirror, most of the light reflects back.The angle with which a ray of light strikes on a reflecting surface is known as the incident angle.The angle with which the light bounces back is known as the reflected angle.
So, according to the principle of reflection if a light ray strikes the surface of a mirror it must bounce back.

When a light ray strikes on a smooth polished surface like a mirror, then the incident angle becomes equal to the reflected angle. In the given question the incident angle is $0^{\circ }$ as it travels along the normal of the mirror. Thus, the reflected angle is also $0^{\circ }$. So, the light ray retraces back to its original path.

Therefore, option (C) is correct..

Note: It must be noted that the principle of reflection of light states that the incident ray, reflected ray and normal must lie on the same plane. If the angle of the surface is inclined at some angle, then the incident angle and the reflected are not equal. Such a type of reflection is known as irregular reflection.