Light is an energy that produces a sensation of vision. We can see objects around us when the light which falls on them gets reflected back in the same medium. Light travels in a straight line and this straight-line path of light in known as a ray of light. A ray of light has both-
- wave nature
- particle nature
Light casts a sharp image of an opaque object due to its straight line path.
If an opaque object of very small size comes in the path of light the light rays bend around it, this explains the wave nature of light, this effect is known as the diffraction of light. Light show us the phenomenon of reflection and refraction too.
When a ray of light falls on opaque objects it bounces back in the same medium this phenomenon is called as reflection. Smooth and polished surfaces like mirror, shiny metals etc. are good reflectors. There are two laws that govern the phenomenon of reflection:
Laws of Reflection
- The angle of incidence is equal to the angle of reflection.
- The incident ray, the normal to the mirror at the point of incidence and the reflected ray all lie in the same plane.
Reflection by a plane mirror:-
Properties of the images formed by a plane are:-
- Size of the image- same size as that of object
- Height of the image- same height as that of object
- Distance of image from the mirror- same as the distance of object from the mirror
- Type of image- Virtual (formed behind the mirror), Erect (in upright position)
- Laterally Inverted- by laterally inverted it means that the right side of the object appears to be the left side of the object.
A spherical mirror is a considered as a part of a sphere with one side polished and other side is reflecting. There are two types of spherical mirrors:-
- Concave Mirror
- Convex Mirror
Concave Mirror- a spherical mirror, whose reflecting surface is facing inward i.e towards the centre of the sphere is known as a concave mirror
Convex Mirror- a spherical mirror, whose reflecting surface is bulging outwards is known as a convex mirror.
A ray of light when travels from an optical medium to another optical medium of different optical densities it bend either towards the normal or away from the normal, depending upon the densities of the two medium this phenomenon is known as refraction. For example light travelling from air to glass or glass to water etc. There are two laws of refraction-
- The incident ray, the normal on the surface of refraction at the point of incidence and the refracted ray, all lie in the same plane.
- The ratio of sine of angle of incidence to the sine of angle of refraction is constant for a given pair media and for a light of a given colour.
sin i ⁄ sin r = constant
The second Law of refraction is also known as the Snell’s Law. The value of constant is the value refractive index of medium two with respect to medium one. The refractive index expresses the extent of deviation of path of the light. Light travels with different speed in different media the value of refractive index of a given pair of media depends upon the speed of light in that media.
The phenomenon of refraction is observed through the lenses. A transparent medium bound by two surfaces of which one or both the surfaces are spherical is known as a lens. There are two types of spherical lenses:-
- Convex Lens
- Concave Lens
Convex Lens- a lens having both the spherical surfaces bulging outwards is known as a convex lens. Convex Lens converges ray of light passing through them and hence are called converging lens.
Concave Lens- a lens having both the spherical surfaces curved inwards is known as a concave lens. Concave lens diverge the ray of light passing through them and hence are called diverging lens.