Question

find power of concave lens of focal length 2.5 cm

Answer 1

P=1/f

Firstly we have to chance cm into metre
So,
f=2.5/100
f=0.025mtr

P=1/f
P=1/-0.025
P=-40 D

Answer 2

Answer:

-40D

Explanation:

Power of a lens = The reciprocal of the focal length in meters.

We first convert the measurement of the focal length to meters.

100 cm = 1 m

We convert the focal length from centimeters to meters as follows :

2.5/100 = 0.025m

The focal length of a concave lens is negative.

f = - 0.025

Power = 1/f

Note : focal length in meters.

Power = 1/-0.025 = -40 D

The power of the focal length is -40D