NEETPhysicsGeometrical OpticsMCQ+4 / −1
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
- A+2 D
- B+20 D
- C+5 D
- DInfinity
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Correct answer: C
Power of lens is given by
$P = {1 \over {f(m)}}$
$${1 \over f} = (\mu - 1)\left( {{1 \over {{R_1}}} - {1 \over {{R_2}}}} \right)$$
$${1 \over f} = \left\{ {{3 \over 2} - 1} \right\}\left( {{1 \over {20}} + {1 \over {20}}} \right)$$
$f = 20$ cm
$$P = {1 \over {20 \times {{10}^{ - 2}}}}$$
$ = 5$ D
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