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 :

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 :

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 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 :

The hypermetropia is a

Rainbows are formed by

Colours of thin soap bubbles are due to :s

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

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

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?