Question

Find the focal length of a lens of power -2.0 D. what type of lens is this

Answer 1

the power of this lens has a negative sign, so this is a concave lens .

Now,

power, P = 1/ f

-2 = 1/ f

f = -1 / 2 m


[converting m into cm]


f = -1 / 2 x 100


so, focal length of lens , f. = -50 cm.

Answer 2

Explanation:

Power of lens, P= 1/f

P= -2D

f= -1/2 = -0.5 m

A concave lens has a negative focal length. Hence, it is a concave lens.