Question

One student uses a lens of focal length 50 cm and another of -50cm. What is the nature of the lens and its power used by each of the

Answer 1

$$f=0.5\ m\\P=\frac{1}{0.5}=2\ D$$

For convex lens,

$$f>0⟹P>0$$

For concave lens,

$$f<0,⟹P<0$$

Lens is convex in the first case and concave in the second case. Power is equal to 2 dioptre in the first case and -2 dioptre in the second case.