Question

The power of convex lens of focal length 20cm in diopter is what?

Answer 1

Answer.

5 D

Explanation:

w. k. t.

power of a lens = 1/focal length of lens in metres

so,

20 CM in metres= 20/100m=1/5 metres.

power of a lens= 1/1/1/5=5 dioptres........

Answer 2

Answer:

The power of the lens is 5D.

Explanation:

The power of a lens is defined as the inverse of its focal length in meters. It is expressed in diopter(D).

$P=\frac{1}{f}$           (1)

Where,

P=power

f=focal length in meter

If the focal length is in cm then equation (1) can be written as,

$P=\frac{100}{f}$             (2)

The focal length of the lens that is given in the question is 20cm.

$P=\frac{100}{20}=5D$

Hence, the power of the lens is 5D.