Question

43. A student uses a lens of focal length 40 cm and another of - 20 cm. The power and focal length of the combination will be: Power of Combination Focal length of Combination (a) - 2.5 D - 40 cm + 2.5 D + 40 cm (C) + 5.0 D + 20 cm​

Answer 1

Answer:

bro first tell please the nature of the lens that is it convex or concave?? after that we can tell that the focal length will be negative or positive

Answer 2

Answer:

Power of focal length 40 cm = 0.4m,,,

p = 1/fp = 1/0.4

p = 10/4

p = 2.5 D

It is a CONVEX lens...

Power of focal length -20 cm = -0.2m,,,

p = 1/f

p = 1/-0.2p = 10/-2

p = -5 D

It is a CONCAVE lens...