Unit 6 Reflection and Refraction of Light
Angle of Incidence:
The incident ray and reflected ray form two angles at the point of incidence:
The angle formed between the normal and the incident ray at the point of incidence is
called the angle of incidence. Similarly, the angle formed between the normal and the
reflected ray at the point of incidence is called the angle of reflection.
Angle of Incidence Formula:
The angle of incidence is equal to the reflected angle through the law of reflection. The
angle of incidence and the angle of reflection is always equal, and they are both on the
same plane along with the normal.
Examples of Angle of Incidence:
Example 1:
Consider a light ray which is incident on a flat surface such that it makes an angle of 10°
with the surface.
Light incident to the surface
What is the angle of incidence?
What is the angle of reflection?
Sketch the diagram for the path of the reflected beam
Solution:
We know that the normal to the surface is always 90°. It is given that the light ray is
making 10° with the surface. Therefore, the angle of incidence is 90°-10°=80°.
From the law of reflection, we know that the angle of incidence is equal to the angle of
reflection. Therefore, the angle of reflection is 80°.
The below diagram is the sketch for the path of the reflected beam:
Path of the reflected beam
Example 2:
The angle at which the light ray strikes the reflective plane surface is 56°. Find:
The angle of incidence
The angle of reflection
The angle made by the reflected ray and the surface
The angle made by the incident and reflected rays
Solution:
Consider the below diagram to answer the questions:
Light striking the reflective surface
Angle of incidence = i = 90°-56°=34°
From the law of reflection, angle of reflection = r = i = 34°
Angle made by the reflected ray and the surface = q = 90°-r = 90°-34°=56°
Angle made by the incident and reflected rays = i+r=34°+34°=68°
Note:
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When a light ray approaches a smooth polished surface and bounces back, it is
known as the reflection of light.
What is the nature of the image formed by the plane mirror?
A plane mirror always forms a virtual and erect image of the object.
The laws of reflection:
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The angle of incidence is equal to the angle of reflection.
The incident ray reflected ray and the normal at the point of incidence all lie in the
same plane.
Types of reflection of light:
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Regular or specular reflection
Irregular or diffused reflection
Type of reflection results in a clear and sharp reflection?
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Specular or regular reflection produces a clear and sharp reflection.
Numerical1: A light ray strikes a reflective plane surface at an angle of 56 with the
surface.
a.) Find the angle of incidence.
b.) Find the angle of reflection.
c.) Find the angle made by the reflected ray and the surface.( q)
d.) Find the angle made by the incident and reflected rays.(sum)
b
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