Question

why you are Mercury column in thermometer first decends slightly and then rises when placed in hot water?​

Answer 1

Any liquid in a container, when heated, at first it's level goes down a little, then rises.

It's because the container volume increases first, before the liquid gets hot. So the level goes down. It takes a little longer to heat up the whole volume of the liquid. A little later, as the liquid gets heated up, it expands faster than the container and the level rises.

In general, coefficient of thermal expansion is higher for liquids than solids.

This is why the mercury level first goes down then rises.

Answer 2

Step-by-step explanation:

Because When placed on hot water, the thermometer itself expands slightly first so the Mercury appears to be descending. After the thermometer expands slightly, the Mercury expands. Hence, Mercury column in thermometer first decends slightly and then rises when placed in hot water