In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. Whatis the reason for this rise in the level of mercury?

The rise in the level of mercury in a thermometer when it comes in contact with a hot object is due to the principle of thermal expansion. Here are the steps explaining this process:

1. When the bulb of the thermometer, which contains a small amount of mercury, is in contact with a hot object, the mercury absorbs the heat.

2. The heat energy causes the mercury atoms to move faster and spread out, a process known as thermal expansion.

3. As the mercury expands, it has no place to go but up into the narrow tube of the thermometer, because the bulb is sealed.

4. The higher the temperature of the object, the more the mercury expands, and the higher it rises in the tube.

5. The level of mercury in the tube corresponds to the temperature of the object, which can be read off the scale on the thermometer.