Question

Q5 (a) What is meant by ‘power of a lens’?
(b) State and define the S.I. unit of power of a lens.
(c) A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with each other. Calculate the lens power of this combination.

Answer 1

Answer:

• (a). Power of a lens is the ability to converge or diverge the ray of light falling on it. Power of a lens is defined as reciprocal of focal length of the lens.
• (b). The power of a lens is defined as the reciprocal of its focal length. It is represented by P. The SI unit of power is dioptre. The power of a convex lens is positive, the power of a concave lens is negative as a concave lens has a negative focal length.

Explanation:

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Answer 2

Answer is in the image.