Question

Write answers the following questions.

(a) Why does an object cast a shadow on a screen?

(b) What is the connection between the formation of shadows and the propagation of light?

(c) Explain what is meant by umbra and penumbra with the help of diagrams.

(d) When does a solar eclipse take place?

Answer 1

(a) We know that light travels in a straight line. When light is blocked by any object or if the comes in its path, then it casts a shadow on the screen.

For example: If we glow a candle in a dark room, and place a book between the candle and a screen, the object casts a shadow on the screen.

(b) The connection between the formation of shadows and the propagation of light is the rectilinear propagation of light.

(c) Umbra and penumbra are two different parts of a shadow of an object. Umbra is the darker part of the shadow (light is completely obstructed). Penumbra is the lesser dark part of the shadow (light is partially obstructed). Umbra is the part of the shadow which is exactly behind the obstacle casting the shadow. Penumbra is the part of the shadow on the outer side of the obstacle.

(d) Solar eclipse takes place when the moon comes between the Sun and the Earth and the three are in a straight line. The shadow of the moon falls on the Earth.