Rainbows are formed by

The refractive index of the material of the prism is √3, then the angle of minimum deviation of the prism is

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

A beam of light composed of red and green rays is incident obliquely at a point on the face of a rectangular glass slab. When coming out on the opposite parallel face, the red and green rays emerge from

A beam of monochromatic light is refracted from vacuum into a medium of refractive index 1.5. The wavelength of refracted light will be

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

A microscope is focussed on a mark on a piece of paper and then a slab of glass of thickness 3cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?

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

Ray optics is valid, when characteristic dimensions are

A body is located on a wall. Its image of equal size is to be obtained on a parallel wall with the help of a convex lens. The lens is placed at a distance d ahead of second wall, then the required focal length will be