Question

Two lenses have power of a) +2D b) -4D. What is nature and focal length of each lens?

Answer 1

Answer:

Converging lens have positive power and diverging lens will have negative power.

Power of lens = 1/focal length of lens(in meters)

i).    +2D = 1/f₁

       f₁ = 1/2 = 0.5m = +50cm (converging lens with focal length 50cm)

ii).   -4D = 1/f₂

       f₂ = 1/-4 = -0.25m = -25cm (diverging lens with focal length 25cm)