Question

What was the power of lens of f= 40 and f=-20

Answer 1

 Power of convex lens, = 100/20. = + 5 D. Power of concave lens, = 100/40. = – 2.5 D. (ii ) Power of ... (iv), Focal length of combination f (in cm), = 100/P. = 100/2.5. = + 40 cm.

Answer 2

power of lens of focal length 40 cm is plus 2.5 dioptre and of f -20 is -5 dioptre