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 power P of a lens is calculated using the formula:

`P = 1/f`

where:

P = Power of the lens (in dioptres, D)

f = Focal length (in metres)

Given:

Power P = 4 D 

Focal length f = 0.25 m

Now apply the formula:

`P = 1/f = 1/0.25 = 4D`

Since the power is positive, the lens is convex.