# A person cannot see beyond 2 m. If he has to read a signboard 4 m away, then the power of the lens required is

By BYJU'S Exam Prep

Updated on: September 25th, 2023

A person cannot see beyond 2 m. If he has to read a signboard 4 m away, then the power of the lens required is -0.25 D. A lens is a transmissive optical device that, via the use of refraction, concentrates or disperses a light beam. While a compound lens is made up of numerous simple lenses that are often aligned along a common axis, a simple lens is made up of a single transparent piece.

## Power of the Lens if a Person cannot See beyond 2m & has to Read Signboard at 4m

The farthest distance that a person can see clearly is referred to as their far point, and the closest distance that they can see well is referred to as their near point. Many people experience vision issues as they age because of an inherited eye condition. To calculate the power of the lens, Lens formula has to be used which is 1/f = 1/v − 1/u or P = 1/f.

By putting the values in 1/f = 1/v − 1/u, we will get,

1/f = 1/(-2) – 1/(-4)

1/f = 1/(-4)

1/f = −0.25m−1

Therefore, the power of the lens will be -0.25 D.

Summary:

## A person cannot see beyond 2 m. If he has to read a signboard 4 m away, then the power of the lens required is

-0.25 D should be the power of the lens if a person cannot see beyond 2 m and he has to read a signboard 4 m away. A lens is a transmissive optical device that concentrates or disperses a light beam through the use of refraction.

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