# A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Given:

A doctor has prescribed a corrective lens of power +1.5 D.

To do: To find the focal length of the lens and to determine the type of lens whether it is diverging or converging.

Solution:

Power of the lens:

The power of a lens implies the ability to bend a light passing through it.

The unit of power of a lens is Diopter$(D)$

The formula for the power of lens:

$\boxed{P=\frac {1}{f}}$

Here,

$P\rightarrow$ Power of the lens

$f\rightarrow$ focal length of the lens

It is given that power of the lens, $P$ = $+1.5\ D$

Substituting the given values we get-

$+1.5=\frac {1}{f}$

Or $f=+\frac {1}{1.5}$

Or $f=+\frac {10}{15}$

Or $f=+0.666\ m=+66.6\ cm$

Therefore,

The focal length of the lens:

The focal length of the lens $f$ is 66.6 cm.

Nature of the lens:

The negative sign $(+)$ implies that the lens is converging in nature. Hence, it is a convex lens.

Updated on: 10-Oct-2022

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