Question

the focal length of a concave lens is 10cm.Calculate its power.​

Answer 1

Answer:

-10D

Explanation:

We know that

Power = 1/ focal length

Also 1m = 0.01cm

Hence 10cm = 0.1m

Focal length of concave mirror is negative

So f = -0.1m

D = 1/-0.1

Power = -10D

Answer 2

Answer:

The focal length of the concave lens = -10 cm.

(Concave lens is also called as diverging lens. The focal length of concave lens is always negative.)

Power is said to be the reciprocal of focal length in m.

Dioptre is the unit of power of lens.

1 dioptre is the power of a lens whose focal length is 1 metre.

Hence, 1 D = 1 m^{-1}.

The power of convex lens is positive.

And, the Power of concave lens is negative.

Therefore, P = 1/f.

Hence, P = 1/-10

⇒ P = 1/-0.1

⇒ P = -10 D