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.

Which of the following phenomenon is not common to sound and light waves?

An astronomical telescope of ten fold angular magnification has a length of 44 cm. The focal length of the objective is :

Colours of thin soap bubbles are due to :s

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 :

A man is 6 ft tall. In order to see his entire image, he requires a plane mirror of minimum length equal to :

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 :

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