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JAMB Physics 2017 Paper

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Question : 25

Total: 49

Determine the focal length of a thin converging lens if the power is 5.0 dioptres

0.1 m
0.2 m
2.0 m
2.5 m

Solution:

Concept:

The power of a lens is the reciprocal of its focal length in metres.

Explanation:

Power is given by

P = \frac{1}{f}

, where

f

is the focal length in metres.

Rearrange the formula to find

f

:

f = \frac{1}{P}

Substitute

P = 5.0

dioptres:

f = \frac{1}{5.0}

f = 0.2 \, \text{m}

Answer:

The focal length is

0.2 \, \text{m}

, which is option B.

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