Laws Of Reflection

What is Law of Reflection?

Law of reflection is defined as

The principle when the light rays falls on the smooth surface, the angle of reflection is equal to the angle of incidence, also the incident ray, the reflected ray, and the normal to the surface all lie in the same plane.

What is Reflection of Light?

The process through which light rays falls on the surface and gets bounced back is known as reflection of light.

Law of Reflection Formula

The law of reflection formula is given as:

 θi = θr

Where,

• θis the angle of incidence
• θis the angle of reflection

What is Angle of Reflection?

The angle of reflection Θr of a ray is the angle measured from the reflected ray to the normal surface.

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

Q1: A ray of light is incident towards a plane mirror at an angle of 30° 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°

According to Law of Reflection,

θi = θr

Hence,

Angle of Reflection = 60°

Q2: A light ray strikes a reflective plane surface at an angle of 54° 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, θi = 90° – 54°=36°

(ii) Angle of Reflection, θr = 36° (As per Law of Reflection)

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

q=90° – r = 90° – 36° = 54°

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

θi = θ=36° + 36° = 72°