Question

Two lenses have power +2D, -4 D respectively. State their nature and focal length of the lens.

Answer 1

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

$P_1=+2D⟹f_1=0.5m=50cm$

since $f$ is positive, it is convex lens.

$P_2=-4D⟹f_2=-0.25m=-25cm$

since $f$ is negative, it is concave lens.