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  4. A biconvex lens has radii of curvature, 20 cm each. If the refractive index of the material of the lens is 1.5, the power of the lens is :

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Q. A biconvex lens has radii of curvature, $20\, cm$ each. If the refractive index of the material of the lens is $1.5$, the power of the lens is :

NEETNEET 2022Ray Optics and Optical Instruments

Solution:

$R _{1}= R _{2}=20\, cm =0.2\, m$
$\mu=\frac{3}{2}$
$P =\frac{1}{ f }=(\mu-1)\left(\frac{1}{ R _{1}}-\frac{1}{ R _{2}}\right)$
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$P =\left(\frac{3}{2}-1\right)\left(\frac{1}{0.2}+\frac{1}{0.2}\right)$
$P =\frac{1}{2}\left(\frac{2}{0.2}\right)=\frac{10}{2}=+5 D$