Question

If the power of the lens is 20d then it's focal length is k cm. Find the value of k

Answer 1

Answer:

the value of k is -20

coz,

wkt ,f=-d

Answer 2

Answer: The value of k is 5

Explanation:

Power of a lens is measure of ability of a lens to converge or diverge the light rays falling on it.

Mathematically, power of a lens is equal to the reciprocal of its focal length.

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

The SI unit of power is 'dioptre' denoted by D.

Focal length of lens = k cm

Focal length of lens = $\frac{k}{100}$ m

Power of lens = $\frac{1}{f}$

Power of lens = $\frac{100}{k}$  D

$20 = \frac{100}{k}\\\\k = \frac{100}{20}$

$k = 5$

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