The magnifying power of a telescope is 9. When it is adjusted for parallel rays, the distance between the objective and the eye piece is found to be 20 cm. The focal length of lenses are

The dispersive power of material of a lens of focal length 20cm is 0.08.What is the longitudinal chromatic aberration of the lens ?

An achromatic convergent doublet of two lenses in contact has a power of + 2D.The convex lens has power + 5D. What is the ratio of dispersive powers of convergent and divergent lenses ?

A ray of light passes through an equilateral prism such that the angle of incidence is equal to the angle of emergence and the latter is equal to 3/4th of the angle of prism. The angle of deviation is

A prism has a refracting angle of 60º. When placed in the position of minimum deviation, it produces a deviation of 30º. The angle of incidence is

A double convex lens of focal length 6 cm is made of glass of refractive index 1.5. The radius of curvature of one surface is double that of other surface. The value of small radius of curvature is

Light takes t₁ sec to travel a distance x in vacuum and the same light takes t₂ sec to travel 10 cm in a medium. Critical angle for corresponding medium will be

A lens of power + 2 diopter is placed in contact with a lens of power –1 diopter. The combination will be have like

A convex lens of focal length f₁ and a concave lens of focal length f₂ are placed in contact. The focal length of the combination is

In a concave mirror, an object is placed at a distance x₁ from focus, and image is formed at a distance x₂ from focus. Then focal length of mirror is