A liquid in a container is heated suddenly. At first the liquid level goes down a little and then the level begins to rise. Explain why.

Explanation

As heating starts, the container receives the heat first and expands in volume. No significant change occurs in the temperature of the liquid in the container. So, initially the volume of the liquid remains approximately unchanged. For this, the liquid level in the container goes down a little. But on prolonged heating, the liquid gradually becomes hot and begins to increase in volume. Generally, the expansion of a liquid is greater than that of a solid. Hence, after some time, the liquid level rises above its initial level.