Zeroth Law of Thermodynamics
It states that if two bodies A and B are in thermal equilibrium with a third body C then A and B are also in thermal equilibrium with each other.
For example :
Thermometer: In case of mercury thermometer, the body temperature (A) is in thermal equilibrium with thermometer tube (C) and thermometer tube (C) is in thermal equilibrium with body (B) i.e. mercury. So body temperature and mercury are in thermal equilibrium as shown in figure.
Explanation :
Let us say TA, TB and TC are the temperatures of the bodies A, B, and C respectively.
Given: A and C are in thermal equilibrium i.e., TA = TC and B and C are in thermal equilibrium i.e., TB = TC then as a consequence of zeroth law, A and B will also be in thermal equilibrium i.e., TA = TB
Note:
- The zeroth law gives the concept of temperature and its measurement.
- Hotness and coldness are feelings associated with heat transfer rate, and temperature is one of the variables that affects the heat transfer.
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