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WAEC Physics 2018 Paper

Question : 18

Total: 50

The diagram above illustrates the mercury-in-glass thermometer used for determining the temperature of a room. Use the data on it to determine the room temperature.

3.3°C
7.0°C
13°C
30.0°C

Validate

Solution:

Concept:

A mercury-in-glass thermometer works on the principle of linear expansion of mercury, so the length of the mercury thread is proportional to the temperature.

Explanation:

From the data on the thermometer, the thread rises

3

cm when the room temperature is

X

The full scale of

100^\circ\mathrm{C}

corresponds to a thread length of

10

cm.

Using the principle of proportionality:

\frac{X - 0}{100 - 0} = \frac{3 - 0}{10 - 0}

\frac{X}{100} = \frac{3}{10}

Cross-multiplying gives:

X = \frac{3 \times 100}{10}

X = 30^\circ\mathrm{C}

Answer:

The room temperature is

30^\circ\mathrm{C}

, so the correct option is D.

30.0^\circ\mathrm{C}

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