Question

Upper fixed point of a thermometer is marked using a _________.

Answer 1

Upper fixed point (UFP) of a thermometer:

1. Upper fixed point of a thermometer is marked using a hypsometer.
2. To mark the upper fixed point (UFP), the thermometer bulb is held in special instrument called hypsometer such that the bulb is maintained at the boiling point of water, and does not touch water.
3. In the hypsometer, pure water is boiled at standard pressure and the steam formed by the boiling water is used to raise the temperature of the bulb.
4. The mercury in the bulb expands and its level in the glass capillary raises.
5. When the level remains steady for few minutes, then this is marked as upper fixed point (UFP).

Thus, upper fixed point of a thermometer is marked using a hypsometer.