Two plane mirrors are positioned at right angles to one another. A ray of light strikes one...

Question:

Two plane mirrors are positioned at right angles to one another. A ray of light strikes one mirror at an angle of 30 to the normal. It then reflects toward the second mirror. What is the angle of reflection (from the normal) of the light ray OFF the second mirror?

Laws of reflection and image formed by the plane mirror:

There are two laws of reflection. They are;

  • The angle of incidence is equal to the angle of reflection.
  • The incident ray, reflected ray and the normal at the point of the incidence all lie in the same plane.

An image of an object formed in a plane mirror is of the same size as the object and are located behind the mirror at the same distance.

Answer and Explanation:

Given:

  • Two mirrors meet at an angle of {eq}90^{\circ}{/eq}.

The ray diagram shown in the figure below shows the path of the light ray that strikes Mirror 1 at an angle of incidence, {eq}30^o {/eq}.

In the above diagram,

  • MA is the incident ray on Mirror 1.
  • AB is the incident ray on Mirror 2.
  • BN is the reflected ray OFF the Mirror 2.

From the first law of reflection the angle of reflection of the light ray OFF the Mirror 2 is {eq}60^o {/eq}.


Learn more about this topic:

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Plane Mirror: Definition & Uses

from Physics 101: Help and Review

Chapter 14 / Lesson 16
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