Question

The power of a lens is - 5d. [2] (i) find its focal length. (ii) name the type of lens.

Answer 1

since

p = 1/ f

-5 = 1/ f

f = - 0.2 m

it is a concave lens

Answer 2

Answer:

1. f = -0.2 m

2. Concave lens

Explanation:

Given that,

Power of the lens, P = -5 D

(a) The reciprocal of the focal length of the lens is called its power. Mathematically, it is given by :

$f=\dfrac{1}{P}$

$f=\dfrac{1}{-5}$

f = -0.2 m

(b) The focal length of a concave lens is negative.