For the given incident ray as shown in figure, the condition of total internal reflection of the ray will be satisfied if the refractive index of block will be

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 :

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

Colours of thin soap bubbles are due to :s

The hypermetropia is a

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 :

Rainbows are formed by

If two mirrors are kept inclined at 60° to each other and a body is placed at the middle, then total number of images formed is :

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