REFLECTION OF LIGHT
When light falls on the surface of an object, some of light is returned back in same medium . The process of sending back the light rays from surface of an object, is called reflection of light.
Most of the objects reflect light. Some objects reflect more light whereas other objects reflect less light.
The objects having polished, shining surfaces reflect more light than objects having unpolished, dull surfaces.
Silver metal is one of the best reflectors of light.
A polished block of silver metal reflects almost all the light falling on it and does not transmit any light through it. But the surface of silver metal is easily scratched and soon becomes rough. So, ordinary mirrors are made by depositing a thin layer of silver metal on the back side of a plane glass sheet. The silver layer is then protected by a coat of red paint. The reflection of light in a plane mirror (or any other mirror) takes place at the silver surface in it. Thus, a plane mirror is a thin, flat and smooth sheet of glass having a shining coating of silver metal on one side. The silver coating is protected by a red paint. These days mirrors are being made increasingly by depositing a thin coating of aluminium metal at the back of a glass sheet (instead of silver coating). This is because aluminium is Front much cheaper than silver and it reflects light very well.
REFLECTION OF LIGHT FROM PLANE SURFACES : PLANE MIRROR
When a ray of light falls on a plane mirror (or any other plane surface), it is reflected according to some laws, called the laws of reflection of light.
Incident ray :
The ray of light which falls on the mirror surface is called the incident ray.
AO is the incident ray of light.
Point of incidence :
The point at which the incident ray falls on the mirror is called the point of incidence.
Point O on the surface of the mirror is the point of incidence (because the incident ray AO touches the mirror surface at this point).
Reflected ray :
The ray of light which is sent back by the mirror is called the reflected ray.
OB is the reflected ray of light. The reflected ray of light shows the direction in which the light goes after reflection from the mirror.
Normal :
Normal is a line which is perpendicular to the mirror at the point of incidence.
The line ON is the normal to the mirror surface at point O.
The normal is a line at right angles to the mirror surface. In other words, normal makes an angle of 90° with the surface of the plane mirror.
Angle of incidence :
The angle between the incident ray and normal is called the angle of incidence.
The incident ray is AO and the normal is ON, so the angle AON is the angle of incidence.
The angle of incidence is denoted by the letter i.
Angle of reflection :
The angle between the reflected ray and normal is called the angle of reflection.
The reflected ray is OB and the normal is ON, so the angle NOB is the angle of reflection.
The angle of reflection is denoted by the letter r.
Laws of Reflection of Light:
The laws of reflection of light are given below :
1. First Law of Reflection.
According to the first law of reflection of light : The incident ray, the reflected ray, and their corresponding normal , all lie in the same plane.
According to the first law of reflection of light : The incident ray, the reflected ray, and their corresponding normal , all lie in the same plane.
2. Second Law of Reflection.
According to the second law of reflection of light : The angle of incidence is always equal to the angle of reflection.
If the angle of incidence is ‘ i ‘ and the angle of reflection is r, then according to the second law of reflection : i = r
The laws of reflection of light apply to all kinds of mirrors like plane mirror, spherical mirrors (concave mirrors and convex mirrors), parabolic mirror etc.
What happens when a ray of light falls normally (or the. Perpendicularly) on surface of a mirror.
light is incident normally on a mirror, it means that it is travelling along the normal to the mirror. So, the angle of incidence (i) for such a ray of light is zero (0). And since the angle of incidence is zero, therefore, according to the second law of reflection, its angle of reflection (r) will also be zero (0). This means that a ray of light which is incident normally on a mirror, is reflected back along the same path.
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