CBSE Class 10 Science 2017 · Paper 31/3/C · Question 3

Light - Reflection and Refraction 1 mark Easy

The focal length of a lens is +25 cm. Write the power of this lens.

Answer

$P = + 4$ D: the power of the lens is +4 dioptre, so it is convex.

P = \frac{1}{f} = \frac{1}{+ 0.25 m} = + 4

D. The power of the lens is

+ 4

dioptre; the positive sign shows that it is a convex (converging) lens.

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