Question

Which of the following statements is true?

Options

• A convex lens has 4 dioptre power having a focal length 0.25 m

•  A convex lens has –4 dioptre power having a focal length 0.25 m

• A concave lens has 4 dioptre power having a focal length 0.25 m

• A concave lens has –4 dioptre power having a focal length 0.25 m

Answer 1

A convex lens has 4 dioptre power having a focal length 0.25 m

Explanation -

The focal length and the power of concave lens is always negative and of convex lens is positive. The relation between power and focal length is,  `"P" = 1/"f"`

Using this formula to find power,

`"P" = 1/"f"`

`= 1/0.25`

= 4D