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WAEC Physics 2017 Paper

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Question : 31

Total: 50

Two plane mirrors are inclined at an angle 20° to each other. Determine the number of images formed when an object is placed between them.

17
18
19
20

Solution:

Concept:

When two plane mirrors are inclined at angle

\theta

, the number of images formed depends on

\frac{360^\circ}{\theta}

.

Explanation:

Here,

\theta = 20^\circ

.

Calculate

\frac{360^\circ}{20^\circ} = 18

.

Since

18

is an even number, the number of images is

\frac{360^\circ}{\theta} - 1

.

So, number of images

= 18 - 1 = 17

.

Answer:

The number of images formed is

17

.

Correct option: A. 17.

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