Question

Under what temperature does the resistivity of mercury completely disappear?
1. 4.2°K
2. 16.2°K
3. 10.2°K
4. 24.2°K

Answer 1

Correct Answer - Option 1 : 4.2°K

Concept:

Superconductivity:

• The electrical resistance of metals and alloys decreases as the temperature is lowered.
• The phenomenon in which the electrical resistivity of many metals and alloys drops suddenly to zero when they are cooled to a low temperature (i.e. nearly equal to liquid helium temperature) is called super-conductivity. Such materials (metals and alloys) are known as superconductors.
• The temperature at which the resistance of the material suddenly falls to zero is known as critical temperature TC.
• At this temperature, the material undergoes a phase transition from a state of normal resistance to a state of super-conductivity. This temperature is also known as a super-conducting transition temperature.

 

Explanation:

If we study the variation of resistance of mercury with temperature, it is found that at very low temperatures the resistance becomes immeasurable. At about 4.2 K the resistance falls sharply and below this temperature, mercury shows no resistance at all.