10th Class Science Light - Reflection and Refraction Reflection of Light

       Reflection of Light

Whenever light falls on an object some of it is reflected and others are absorbed by the surface. If the light is not reflected by the surface, i.e. all the light is absorbed by the surface, then the object will appear black, like black board or black hole, which is not visible to us. If the light falls on a polished surface, it gets reflected back in the same plane from where it is incidented. This bouncing back of light, after striking a polished surface, is called reflection of light.

Silver metal is considered to be one of the best reflector of light.

Reflection of light shows the particle nature of light. For example, when a rubber cricket ball is strike against a wall it bounces back in the opposite direction, or in other words it is reflected back by the wall. Similarly, if we try to see objects in a dark room it is not visible to us, but if we switch on the light it becomes visible to us. This is because when we switch on the light, the light falls on the object and is reflected back and absorbed by our eyes, and hence we are able to visualize the objects.

Thus on the basis of above observation the laws of reflection has been formulated as below:  

           There are Two Laws of Reflection. These are

• The incident ray, the reflected ray, and the normal all lies on the same plane,
• The angle of incidence is equal to the angle of reflection.

As we know that the silver metal is the best reflector, we can make an ordinary mirror simply by coating a layer of silver metal on the surface of glass. A plane mirror is a good reflector of light. The reflecting surface is divided into two category as plane and spherical surfaces.

            The Spherical Mirror is Again of Two Types

• Concave Mirror
• Convex Mirror

             Concave Mirror

The mirror which is curved inwards is called a concave mirror. It is also known as converging mirror. It converges the ray of light falling on its surface at a point on the surface..

             Convex Mirror

The mirror which is curved outward is called a convex mirror. It is also known as diverging mirror.

The centre of curvature of a spherical mirror is the centre of the hollow spherical surface of which mirror is consider to be the part. The centre of curvature does not lay on the mirror, it lies in front of the concave mirror and behind the convex mirror. The distance between the pole and centre of curvature of the mirror is called the radius of curvature. It is represented by letter R.

Pole is defined as the centre of the mirror and it lies on the mirror. It is normally denoted by P. The principle axis is the imaginary line which passes through the pole of the mirror. The principle axis is always perpendicular to the surface of the mirror.

The centre of curvature, pole, focus, all lies on the principal axis. The focus is defined as the point on the principal axis at which ray of light converges after reflection. It lies at the midpoint between the centre of curvature and pole of the mirror. It is denoted by f. The distance between the pole and focus is called the focal length. It is expressed by \[f=\frac{R}{2}\].

The portion of a mirror from which the reflection of light actually takes places is called the aperture of the mirror. It is also the diameter of the spherical surface or also the size of the spherical mirror.