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JAMB Physics 2014 Paper

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Question : 25

Total: 41

The focal length of a concave mirror is 2.0cm. If an object is placed 8.0cm from it, the image is at

2.7m
2.0m
2.3m
2.5m

Solution:

Concept:

For a concave mirror, the mirror formula relates the object distance, image distance, and focal length.

Explanation:

Use the mirror formula:

\frac{1}{f} = \frac{1}{u} + \frac{1}{v}

.

Given:

f = 2.0\,\mathrm{cm}

and object distance

u = 8.0\,\mathrm{cm}

.

Substitute the values:

\frac{1}{2} = \frac{1}{8} + \frac{1}{v}

.

Rearrange:

\frac{1}{v} = \frac{1}{2} - \frac{1}{8}

.

Compute:

\frac{1}{v} = \frac{4 - 1}{8} = \frac{3}{8}

.

Thus,

v = \frac{8}{3} = 2.67 \approx 2.7\,\mathrm{cm}

.

The image is formed

2.7\,\mathrm{cm}

from the mirror.

Answer:

A.

2.7\,\mathrm{cm}

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