Question

Explain the following:
(a) A coin placed at the bottom of a vessel appears to be raised when water is poured in the vessel.
(b) A straight stick partly dipped in water obliquely, appears to be bent at the surface of water.
(c) The sun is seen before the sunrise and after the sunset.

Answer 1

(a) The coin at A appears to be at B i.e., depth of coin observed is less than actual depth at A.
The ray of light starting from A (denser) medium bends away from the normal. Due to refraction of light the coin appears at B at a lower depth. Hence in the same way the depth of water appear to be less deep.
(b) The phenomena is due to REFRACTION OF LIGHT when light passing from denser (water) medium to rarer (Air) medium appears to come from Q , Virtual image inspite of Q. Same is true for another point of stick inside water. Stick appears to be raised or bent.
(c) EARLY SUNRISE and SUNSET: At sun Rise : When the Sun is just below the horizon, the light from the Sun suffers refraction from RARE to DENSER medium (As atmosphere is warmer than layers near the earth at that time) bends towards the normal at each refraction. Due to continuous bending oflight rays, the Sun can be seen even when its actual positionis just below the Horizon. As a result the Sun is seen in advance, two minutes before it rises above the horizon in the morning.
Similarly, in the evening Sun is seen delayed by 2 minutes longer above the horizon after the Sun set.