Test Index

JAMB Physics 2010 Paper

Question : 22

Total: 47

Solution:

Concept:

A concave mirror forms an image whose size can be found using the mirror formula and the magnification formula.

Explanation:

Take object distance

u = 15\ \mathrm{cm}

and focal length

f = 5\ \mathrm{cm}

The mirror formula is

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

Substitute the values:

\frac{1}{v} + \frac{1}{15} = \frac{1}{5}

Rearrange:

\frac{1}{v} = \frac{1}{5} - \frac{1}{15} = \frac{3 - 1}{15} = \frac{2}{15}

Therefore,

v = \frac{15}{2} = 7.5\ \mathrm{cm}

Magnification,

m = \frac{v}{u} = \frac{7.5}{15} = 0.5

Image height

= m \times \text{object height} = 0.5 \times 4\ \mathrm{cm} = 2\ \mathrm{cm}

Answer:

The size of the image is

2\ \mathrm{cm}

. The correct option is A.

Go to Question:

Prev Question

Next Question