Question

How are power and focal length of a lens related? A student has two lenses
of focal length 50 cm and 25 cm respectively. Help him/her to choose the
lens to obtain more convergent light​

Answer 1

Answer:

Power and focal length of a lens are inversely related or proportional to each other, i.e., more the focal length less will be the power & less the focal length more will be the power.

Power (P) = 1/focal length (f)

Given,

f1 = 50cm

f2 = 25cm

Now,

P1 = 1/50 = 0.02D

P2 = 1/25 = 0.04D

since, P1<P2

so, the student should use the lens with focal length of 25cm to obtain more convergent light.