Question

find the focal length of a lens of power -2.0 what type of lens is this?

Answer 1

P=1/f

therefore
we have P=2.0
1/2.0=1/2=0.5m Is the answer

and the lens is a concave lens.

Answer 2

★$\large\mathcal\red{Power\:\: of \:\:lens (P) = 1/f}$

→P = -2D

→f = -1/2 = -0.5 m

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