# Find the focal length of a lens of power -2.0 D. What type of lens is this?

By BYJU'S Exam Prep

Updated on: September 25th, 2023

The focal length of a lens of power -2.0D is -0.5m. It is a concave lens.

The lens’s power is defined as the reciprocal of its meter-long focal length (m).

Power of lense = 1/ focal length in meter.

Power of lens (P) = 1/f

P = -2D

f = -1/2 = -0.5 m

The focal length of a concave lens is negative. It is a concave lens as a result.

### Power of lens

The degree of convergence or divergence of the light rays hitting a lens is measured by its power. The focal length of the lens determines how much convergence or divergence occurs. As a result, we define the lens’ power as the focal length times its reciprocal. It’s stated as,

Lens power (P) equals 1/f

where f is the lens’s employed focal length. Dioptre is the SI unit of power (D). Convex lenses have a potential for positive power, whilst concave lenses have a potential for negative power.

### Concave lens

A concave lens is one that bends a straight light beam away from the source and focuses it into a distorted, upright virtual image. Both actual and virtual images can be created using it. At least one internal surface of concave lenses is curved. Since it is rounded at the centre and bulges outward at the borders, a concave lens is also known as a diverging lens because it causes the light to diverge. Since they make distant objects appear smaller than they actually are, they are used to cure myopia.

Summary:-

## Find the focal length of a lens of power -2.0D. What type of lens is this?

A lens with a power of -2.0D has a focal length of -0.5m. The lens is concave. In order to concentrate a straight light beam into a distorted, upright virtual image, a concave lens must first bend the beam away from the source. It can produce real-world and digital images.

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