Question

Doctor suggest a lens of power 0.5D to a person calculate the focal length

Answer 1

Given :

Power of the lens = 0.5 D.

To find :

The focal length

Solution :

We know that,

The power of a lens is inversely proportional to its focal length so, a lens of short focal length has more power whereas a lens of long length has less power.

The unit of power of a lens is dioptre.

» The power is the reciprocal of the focal length that is

$\boxed{ \bf P = \dfrac{1}{f} }$

where,

• P denotes power of the lens
• f denotes the focal length

By, substituting the given values in the formula,

$\dashrightarrow\sf P = \dfrac{1}{f}$

$\dashrightarrow\sf 0.5 = \dfrac{1}{f}$

$\dashrightarrow\sf f = \dfrac{1}{0.5}$

$\dashrightarrow\sf f = 2 \: m$

Thus, the focal length of the lens is 2m.