Question

Two lenses have power of 2D and -4D. Find the nature and focal length of each lens

Answer 1

CASE 1:
Here P=+D Since power is positive , so the lens is convex lens
Focal length, f = 1/P=1/2=0.5m=50cm
CASE 2:
Now,P=-4 Since power is negative ,so lens is concave.
Focal length,f=1/P=1/-4=-0.25m=-25cm