Define focal length.

a) An object is kept between centre of curvature and principal focus of a concave mirror. Write the nature of the image formed. b) Define focal length of a convex mirror. Write the relationship between focal length and radius of curvature of a convex mirror.

Define the focal length of mirror

Define the focal length of a spherical mirror.

Convex lens of focal length A and concave lens of focal length B are kept in contact, then the effective focal length of system is .......

A convex lens of focal length f is put in contact with a concave lens of the same focal length. The equivalent focal length of the combination is :

A convex lens of focal length 'f' is placed in contact with a concave lens of the same focal length. The equivalent focal length of the combination is

Two thin lenses, one of focal length + 60 cm and the other of focal length – 20 cm are put in contact. The combined focal length is