Reflection of Light – Definition, Law of Reflection

Reflection of Light 

Introduction

An object reflects certain amount of light falling on it. When this reflected light enters our eyes, we are able to see it. A transparent glass object lets almost all the light falling on it to pass through. That’s why we are able to see through it. Opaque objects do not let light to pass through themselves. They absorb and reflect most light that falls on them. A mirror reflects most of the light that falls on its surface. That’s why it is able to produce an image of an object. Generally, highly polished surfaces reflect more amount of light falling on them. In this section we will be looking at the reflection of light from various surfaces. 

Explanation

Reflection of light: 

Reflection of light is a phenomenon of bouncing back of light from the surface of an object. 

The surface that reflects light is called a reflecting surface. 

A ray of light that hits the reflecting surface is called an incident ray. 

The incident ray after reflecting off the surface is called the reflected ray. 

The point at which the incident hits the reflecting surface is called the point of incidence. 

An imaginary line is always drawn perpendicular to the reflecting surface at the point of incidence, called the normal. 

The angle made by the incident ray with the normal is called the angle of incidence (i). 

The angle made by the reflected ray with the normal is called the angle of reflection (r). 

Laws of reflection: 

The laws of reflection are, 

1. The incident ray, the reflected ray and the normal at the point of incidence, all lie on the same plane. 

2. The angle of incidence is equal to the angle of reflection.  

                                     i = r 

The laws of reflection hold always. 

An incident ray hitting the reflecting surface is said to be incident normally on the surface if it goes along the normal 

The reflected ray follows the same path as that of the incident ray but in opposite direction. 

Spherical mirrors: 

The most common curved reflecting surface which are widely used are the spherical mirrors. 

A spherical mirror is usually made by cutting out a piece from a hollow spherical glass structure. 

One of the surfaces of this piece is then silvered. 

The inner surface of the piece is called the concave surface and the outer bulged out surface is called the convex surface. 

If the outer convex surface is silvered, the inner concave surface is capable of reflecting light. This mirror in which the concave surface is the reflecting surface is called a concave mirror. 

If the inner concave surface is silvered, the outer convex surface is capable of reflecting light. This mirror in which the convex surface is the reflecting surface is called a convex mirror. 

The convex surface of a concave mirror and the concave surface of a convex mirror are rough surfaces. 

Reflection by spherical mirrors: 

The two laws of reflection also hold for the reflection from spherical surfaces. In other words, the incident ray, the reflected ray and the normal at the point of incidence all lie on the same plane and also the angle of incidence and the angle of reflection are equal to each other for spherical mirrors as well. 

Summary

1. An object reflects certain amount of light falling on it. When this reflected light
   enters our eyes, we are able to see it.
2. Generally, highly polished surfaces such as the mirror surface reflect most of the
   light falling on them.
3. Reflection of light is a phenomenon of bouncing back of light from the surface of an
   object.
4. The incident ray, the reflected ray and the normal at the point of incidence, all lie on
   the same plane.
5. The angle of incidence is equal to the angle of reflection. i=r
6. The laws of reflection hold always.
7. An incident ray hitting the reflecting surface is said to be incident normally on the
8. surface if it goes along the normal.
9. The spherical mirror in which the curved in surface is the reflecting surface is
10. called a concave mirror.
11. The spherical mirror in which the bulged-out surface is the reflecting surface is
12. called a convex mirror.
13. The two laws of reflection hold for the reflection of light by spherical mirrors.