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If the focal length of a converging lens is 0.25 m then the power of this lens is ______ dioptre.

Asked in GSEB Board July 2021 · Lens maker's formula and power

Answer: (3) +4

Step-by-step solution

Given: a converging lens with f=+0.25 m.

Idea: power is the reciprocal of the focal length in metres, P=1/f, and it carries the sign of f; converging lenses have positive f.

P=1/(0.25).

So P=+4 dioptre.

The shorter the focal length, the more strongly the lens bends light and the larger its power.

Why the other options are wrong

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