# A student uses a lens of focal length- 50 cm. What is the nature of the lens and its power?

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A student uses a lens of focal length- 50 cm. What is the nature of the lens and its power?

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Since the focal length is negative, therefore the lens is concave lens because the focal length of concave lens is negative.

P (in diopter) = $\frac{1}{f(in\,meters)}$

F = -50cm = -0.5m (1m = 100cm)

⇒ P = -$\frac{1}{0.5}$= -2 D

Hence power of lens is -2 Dioptre.