A lens has power 4D. Find the focal length that lens.
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Power of a lens is determined by the formula$\text{P}=\frac{1}{\text{F}}$ (when focal length is in meters) and
$\text{P}=\frac{100}{\text{F}}$ (when focal length is in centimeters).
Here, the power is given as 4 diopters. On equating we get,$4=\frac{100}{\text{F}}$
$\text{F}=\frac{100}{4}$
$=25\text{cm}$
Hence the focal length of lens is 25cm.
$\text{P}=\frac{100}{\text{F}}$ (when focal length is in centimeters).
Here, the power is given as 4 diopters. On equating we get,$4=\frac{100}{\text{F}}$
$\text{F}=\frac{100}{4}$
$=25\text{cm}$
Hence the focal length of lens is 25cm.
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