A. the intensity of light emitted by them changes with time
B. the distance of the stars from the earth changes with time
C. the refractive index of the different layers of the earth's atmosphere changes continuously, consequently the position of the image of a start changes with time
D. the light from the star is scattered by the dust particles and air molecules in the earth's atmosphere
Correct Answer: the refractive index of the different layers of the earth's atmosphere changes continuously, consequently the position of the image of a start changes with time
6. Planets do not twinkle because
Options
A. they emit light of a constant intensity
B. their distance from the earth does not change with time
C. they are very far away from the earth resulting in decrease in intensity of light
D. they are nearer to earth and hence we receive a greater amount of light and, therefore minor variations in the intensity are not noticeable
Correct Answer: they are nearer to earth and hence we receive a greater amount of light and, therefore minor variations in the intensity are not noticeable
7. On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because
Options
A. mercury is a metal
B. density of mercury is greater than that of water
C. cohesion of mercury is greater than its adhesion with glass
D. cohesion of water is greater than its adhesion with glass