Question

the power of a convex lens of focal length 20cm in diopter unit is

Answer 1

A diopter is the unit of measure for the power of a refractive index of a lens.

It is usually the reciprocal of the focal length of a lens.

It is denoted by D.

Formulae :

D = 1/f where F is the focal length and D is the power of the lens in Diopter.

From the question above given the focal length is 20cm we can get the power of the lens using this formula.

We first convert the cm to meters :

20/100= 0.2m

D =1/0.2

=5 Diopters

Answer 2

Answer:

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Explanation:

Focal of convex lens(f)=+20cm=20/100=+.20m

44P=1/f=1/.20=100/20=+5D$$

focal length of concave lens(f)=−10cm=−10/100=−.1m

P=1/−.1=−10D

power of combination=5−10=−5D