Question

We cannot use mercury thermometer at low temperatures because:

• A. Glass might break down at low temperature.
• B. Heat does not flow from the body whose measurement we are taking with the thermometer.
• C. At low temperatures mercury becomes transparent and it becomes difficult to take the readings.
• D. Mercury freezes at low temperatures.

Answer 1

Answer: (D)

Mercury freezes at low temperatures.

Mercury, which is used as a thermometric liquid, has the following characteristic properties:
1. Mercury has a high boiling point of about ${357}^{\circ }$C and therefore can be used to measure temperatures as high as ${357}^{\circ }$C.
2. Mercury has a freezing point of about $-{39}^{\circ }$C and hence it is suitable in thermometers to record low temperatures (although not very low temperatures).
3. Mercury is opaque and has a shining silvery colour of its own, making it clearly visible in the capillary tube of a thermometer.

4. Mercury needs very little heat to expand and so it can easily measure the temperature of a body without causing a decrease in the body's temperature.
5. Mercury does not stick to the side of the glass capillary tube of a thermometer. Therefore, it allows accurate temperature measurement.
6. Mercury is a good conductor of heat.
7. Mercury is relatively expensive.