Question

Give reasons.

(a) The sun, the earth and the moon must be in a straight line for an eclipse to occur.

(b) The penumbra is faint.

(c) An aeroplane or a bird does not cast a shadow upon the earth.

(d) We get an upside down image in a pinhole camera.

Answer 1

(a) The Sun, the Earth and the moon must be in a straight line for an eclipse to occur because the moon (or the Earth) blocks the light coming from the Sun and forms a shadow on the Earth (or on the moon).

(b) The penumbra is faint because light is partially obstructed in that region.

(c) An aeroplane or a bird does not cast a shadow upon the Earth because distance between an aeroplane or a bird and the Earth is much more as compared to the area blocked by them.

(d) In a pinhole camera, image of the object is formed due to linear propagation of light, which gives an upside image.

Refer to the above figure, the ray of light travelling from the top of the tree will reach M’ on the screen of the camera and the ray of light travelling from the bottom of the tree will reaches at point N’ on the screen of the camera. Therefore, the image formed is inverted.