Question

Q.2 Which of the following statements is true?
(a) A convex lens has 4 dioptre power having a focal length - 0.25 m
(b) A convex lens has –4 dioptre power having a focal length 0.25 m
(c) A concave lens has 4 dioptre power having a focal length 0.25 m
(d) A concave lens has –4 dioptre power having a focal length -0.25m

Answer 1

Explanation:

D no explanation please

Answer 2

Answer:

Option(A)

Explanation:

A dioptre, is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in meters (that is, 1/f metres). It is thus a unit of reciprocal length.

P = (1/0.25) = 4

As the value is positive, it is a positive lens, that is, convex.

Therefore,

A convex lens has 4 dioptre power having a focal length 0.25 m.

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