A beam of light converges to a point on a screen S. A mirror is placed in front of the screen at a distance of 10cm form the screen. It is found that the beam now converges at a point 20cm in front of the mirror. Find the focal length of the mirror.

A converging beam of light forms a sharp image on a screen. A lens is placed in the path of the beam at 10 cm from the screen. It is found that the screen has to be moved 8 cm further away from the lens to obtain a sharp image. Find the focal length and nature of the lens.

A beam of light converges at a point P. Now a concave lens of focal length -16 cm is placed in the path of the convergent beam 12 cm from P The point at which the beam converges now is

A beam of light converges at a point P. Now a convex lens of focal length 30 cm placed in the path of the convergent beam 12 cm from P. The point at which the beam converges now is

A converging lens and a converging mirror are placed with their principal axis coinciding. Their separation equals 40cm. A point source S is placed on the principal axis at a distance of 12 cm from the lens as shown in Fig. It is found that the final beam comes out parallel to the principal axis. Focal length of the lens equals 15 cm. Find the focal length of the mirror.

A beam of light converges at a point P. Now a convex lens is placed in the part of the converngent beam at 15 cm from P. At what point does a beam converge if the convex lens has a focad length 10 cm ?

A beam of light converges to a point P. A lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is (a) a convex lens of focal length 20 cm. (b) a concave lens of focal length 16 cm.

A beam of light converges to a point P . A lens is placed in the path of the covergent beam 12 cm from P . At what point does the beam converge if the lens is (a) a convex lens of focal length 20 cm (b) a concave lens of focal length 16 cm ?

An object is placed in front of a mirror at a distance of 60cm . If its two times diminished image is formed on the screen, the focal length of the mirror is