Question

 If power of lens is -10D what is its focal length? Which type of lens it is?​

Answer 1

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▪️The focal length of the lens is -200 cm.It is a concave lens.

$\underline\mathbf{solution}$

▪️The power of a lens is -0.5 D. It is required to find the focal length of the lens. The relation between the focal length and the power of a lens is given by

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

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

$f = \frac{1}{ (- 0.5)}$

$f = - 2m$

$f = - 200m$

▪️So, the focal length of the lens is -200 cm. Since, it is negative, it must be a concave lens.