The knowledge of the laws of reflection is a prerequisite to this article. To recap, the laws of reflection state that,

- The angle of reflection of the light reflected from a surface is equal to the angle of incidence at the point of reflection.
- The reflected ray, the incident ray and the point of reflection all lie on the same plane.

## What is Angle of Reflection?

The angle of reflection \(\Theta _{r}\) of a ray is the angle measured from the reflected ray to the normal surface.

### What are Laws of Reflection?

According to Law of Reflection,

\(\Theta _{i}=\Theta _{r}\)

Where,

\(\Theta _{i}\) = angle of incidence.

\(\Theta _{r}\) = measurement between the ray and a line normal to the surface that intersects the surface at the same point as the ray.

### Calculation of Angle of Incidence and Angle of Reflection:

- The angle of incidence and the angle of reflection are calculated by drawing a normal line which is perpendicular to the reflecting surface.

## Examples of Laws of Reflection

**Q:** A ray of light is incident towards a plane mirror at an angle of \(30^{\circ}\) with the mirror surface. What will be the angle of reflection?

**Ans:**

Since the angle of incidence is measured between the incident ray and the normal, so, here the angle of incidence is not \(60^{\circ}\).

According to Law of Reflection,

\(\Theta _{i}=\Theta _{r}\)

Hence,

Angle of Reflection = \(60^{\circ}\)

**Q:** A light ray strikes a reflective plane surface at an angle of \(54^{\circ}\) with the surface.

(i) Calculate the angle of incidence.

(ii) Calculate the angle of reflection.

(iii) Calculate the angle made by the reflected ray and the surface.

(iv) Calculate the angle made by the incident and reflected rays.

**Ans:**

(i) Angle of incidence, \(\Theta _{i}\) = \(90^{\circ}-54^{\circ}=36^{\circ}\)

(ii) Angle of Reflection, \(\Theta _{r}\) = \(36^{\circ}\) (As per Law of Reflection)

(iii) Angle made by the reflected ray and the surface,

\(q=90^{\circ}-r=90^{\circ}-36^{\circ}=54^{\circ}\)

(iv) Angle made by the incident and reflected rays,

\(\Theta _{i}+\Theta _{r}=36^{\circ}+36^{\circ}=72^{\circ}\)

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