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 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 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 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 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 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.