A tank is filled with a liquid to a depth of 80 cm. A point source of light is placed at the center of the bottom. The area of the surface of the liquid through which light from the source can emerge out is: (Take refractive index of liquid = 2√3)

The magnifying power of an astronomical telescope in normal adjustment is 10 and the focal length of its eyepiece is 20 cm. The focal length of its objective lens will be:

If the speed of light is 2.12 × 108 m/s inside the medium of an equilateral prism, find the angle of minimum deviation (δm). (Take speed of light in vacuum c = 3 × 108 m/s, sin 45° = 0.707)