If the refractive indices of crown glass for red, yellow and violet colours are 1.5140, 1.5170 and 1.5318 respectively and for flint glass are 1.6434, 1.6499 and 1.6852 respectively, then the dispersive power for crown and flint glass are respectively

A person with a defective eye has his far point at infinity. But his near point is at 50 cm from the eye. The lens to be used to bring the near point to 25 cm is

A simple ‘two-lens telescope’ has an objective of focal length 50 cm and an eye-piece of focal length 2.5 cm. The telescope is pointed at an object at a very large distance which subtends an angle of 1 milli radian on the naked eye. The eye-piece is adjusted so that the final virtual image is formed at infinity. The size of the real image formed by the objective is

If Young’s experiment is performed using two separate identical sources of light instead of using two and one single source, then

A convex lens of focal length 50 cm and a concave lens of focal length 10 cm are placed with their optic centres on the same axis and with a distance d between them. For what value of d will a parallel beam of light incident on the convex lens leave the concave lens as a parallel beam?

Magnifying power of an Astronomical Telescope for distant objects is 8. If the objective and the eye lens are at a separation 45 cm and the final image is formed at infinity, focal lengths of objective and the eye lens are

Dispersive powers of the materials of two lenses A and B are in the ratio 5 : 4. If the achromatic combination of these two lenses placed in contact is a convergent lens of focal lengths of lenses A and B, respectively are

A lens of unknown nature (convex/concave) and of focal length 20 cm forms an erect image 4 times the size of an object. Determine the nature of lens and also the distance of object from the lens