Question

If the power of a lens is -4.0 D, then it means that the lens is a ______.

Options

• concave lens of focal length -50m

• convex lens of focal length +50cm

• concave lens of focal length -25cm

• convex lens of focal length -25m

Answer 1

If the power of a lens is -4.0 D, then it means that the lens is a concave lens of focal length -25cm.

Explanation:-

P = -4 D

`P=100/(f(cm))`

`f(cm)=100/P`

`100/-4=-25"cm"`

Negative focal length means concave lens. Concave lens of focal length -25cm.