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WAEC Physics 2019 Paper

Question : 34

Total: 49

Solution:

Concept:

Water normally expands when heated, but between

0\,{}^\circ\text{C}

and

4\,{}^{\circ}\text{C}

it shows unusual behaviour.

In this range, water contracts on heating instead of expanding.

This unusual behaviour is called the anomalous expansion of water.

Explanation:

Consider water at

0\,{}^{\circ}\text{C}

As it is heated from

0\,{}^\circ\text{C}

4\,{}^{\circ}\text{C}

, its volume decreases.

So, water contracts in this temperature range.

Above

4\,{}^{\circ}\text{C}

, water expands normally with increasing temperature.

Thus, the maximum density of water occurs at

4\,{}^{\circ}\text{C}

The anomalous expansion is therefore limited to the range

0\,{}^\circ\text{C}

4\,{}^{\circ}\text{C}

This is why aquatic life survives in cold climates — ice forms at the top while water below remains near

4\,{}^{\circ}\mathrm{C}

Hence, the correct option is the one that states

0\,{}^{\circ}\text{C}

4\,{}^{\circ}\text{C}

Answer:

0\,{}^\circ\text{C}

4\,{}^{\circ}\text{C}

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