Question

(iii) The power of a convex lens of focal length 25 cm is.
(a) + 4.0 D (b) 0.25 D (C) – 4.0 D (d) - 0.4 D​

Answer 1

Answer:

a +4d

Explanation:

p =1/f it should be in d and cm should be converted in to meter remember .

Answer 2

The power of a convex lens of focal length 25 cm is  + 4.0 D (option-a).

Given: Focal length of the lens, f = 25 cm

To Find: power of the lens, P

Solution:

To calculate P, the formula used:

• Power of the lens = 1 / focal length of the lens
• P = 1/ f

Applying the above formula:

P = 1/ f

   = 1/ 25

First convert cm into m:

1 m = 100cm

100 cm = 1m

25 cm = 1 / 100 x 25

           = 25 / 100

           = 1 / 4

25 cm  = 0.25 m

Putting the value in the formula:

P = 1 / f

P = 1 / 0.25

  = 100 / 25

  = 4

P = +4D

The positive sign is used because the lens is a convex lens.

Hence, the power of a convex lens of focal length 25cm is +4,0D.