Light travels through a glass plate of thickness t and refractive index μ. If c is the speed of light in vacuum  the time taken by light to travel this thickness of glass is :

Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens when immersed in a liquid of refractive index of 1.25 will be :

A telescope has an objective lens of 10cm diameter and is situated at a distance of one kilometre from two objects. Find out the minimum distance between these two objects, which can be resolved by the telescope, when the mean wavelength of light is 5000 Å.

A convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together. What will be their resulting power?

Which of the following phenomenon is not explained by Huygen's construction of wavefront?

A lens is placed between a source of light and a wall. It forms images of area A₁ and A₂ on the wall, for its two different positions the area of the source of light is :

If f_v and f_n are the focal lengths of a convex lens for violet ad red light respectively and F_V and F_R are the focal lengths of concave lens for violet and red light respectively, then we have :

Pick out the longest wavelength from the following types of radiations.

Interference is possible in

The hypermetropia is a