Laws of Reflection
Laws of Reflection
It is found that the reflection of light, from a Surface, always take place in a well defined manner according to the rules. We call these two rules as the two laws of reflection. We must, however, first know some terms to understand and explain the two laws of reflection.
(i) The ‘Point of incidence’ and the ‘Normal’: The Point of incidence is that point on the Surface of the mirror where the incident ray falls. A line Perpendicular to the Surface, at the Point of incidence, is known as the ‘Normal.’
(ii) The incident ray and the Reflected ray:The ray of light, coming towards the mirror, is called the incident ray. Similarly, the ray of light, which turns back after ‘reflection’ from the mirror Surface, is called the reflected ray.
(iii) Angle of incidence and Angle of Reflection:The angle between the incident ray and the normal at the point of incidence, is known as the angle of incidence. Similarly, the angle between the normal and the reflected ray, at the point of incidence, is called angle of Reflection
.
(iv) The Plane of incidence and the Plane of Reflection: The Plane, defined by the incident ray and the normal, at the point of incidence, is called the Plane of incidence. Similarly, the plane defined by the reflected ray and the normal, at the point of incidence, is called the plane of reflection.
First Law:
The incident ray, the normal at the point of incidence and the reflected ray, all lie in the same Plane.
Second Law:
The angle of incidence and the angle of reflection are equal to each other.
Illustration: The incident ray makes an angle of 30 degree with the normal. Find the angle of reflection.
Solution: Given, the angle of incidence
According to the laws of reflection
Therefore
Illustration: The incident ray makes an angle of 30 degree with the surface. Find the angle of reflection.
Solution: Given, the ray makes an angle of 30 degree with the surface
And we know the normal makes an angle of with the surface.
From the figure:
angle of incidence
According to the laws of reflection
Therefore
Note: When the ray of light falls normally or perpendicular on the surface of a plane mirror.
Then the angle of incidence is
According to the laws of reflection
So
Hence the ray which is incident normally on a mirror is reflected back along the same path.
Why is Incident Ray always shown by a line with arrow towards the mirror? | |||
| Right Option : C | |||
| View Explanation |
Which of the following are correct ? (a) The ray of light, which turns back after ‘reflection’ from the mirror surface, is called the incidence ray . (b) A line perpendicular to the surface, at the point of incidence, is known as the Normal. | |||
| Right Option : B | |||
| View Explanation | |||
The perpendicular drawn at any point on a mirror is called ______________ | |||
| Right Option : C | |||
| View Explanation | |||
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