light 2

Take a small concave mirror.Allow some rays of sunlight to fall on it . Since these rays come from a great distance they are considered to be parallel to each other.

Move a paper screen in front of the mirror.We will see that , at a certain point , a clear image of the sun is obtained.This point is known as th principal focus(F) of the mirror.

The focal length (f) is the distance between the pole and the principal focus.

A lens is a piece of glass or transparent material with curved surfaces.A magnifying glass that is used to see things bigger is an example of a lens.

Lenses are mainly classified into convex or concave lenses.

A convex lens is thicker in the middle than the edges.Rays of light converge in mos cases after passing through a convex lens.Hence , they are also called converging lenses.

A concave lens is thinner in the middle than at the edges.Rays of light diverge after passing through concave lenses. Hence , they are called diverging lenses.

1) Reflection of light by a smooth , polished surface is regular reflection.

2) The image formed by a plane mirror is as far from the mirror as the object is in front of the mirror.

3) If a spherical mirror is cut out from a sphere , the centre of the sphere is the central of curvature.

4) In a convex mirror , the light rays always diverge after reflection.

5) Convex mirror give only virtual images.

6) Concave mirrors are used in headlights and searchlights.

7) Concave lenses are also called diverging lenses.

8) A ray passing through the optical of a lens emerges undeviated.

9) In most cases , rays of light converge after passing through a convex lens.

LIGHT LESSON IS DONE