Zeroth Law of Thermodynamics

Zeroth Law of Thermodynamics

Two bodies are said to be in thermal equilibrium if no transfer of heat take place when they are placed in constant. Now we can say that the Zeroth law of Thermodynamics as follows:

If two bodies A and B are in thermal equilibrium and A and C are also in thermal equilibrium then B and C are also in thermal equilibrium.

A = B and A= C then B = C in thermal equilibrium

It’s a matter of observation and experience that is described in the Zeroth law. For example: if two persons A and B know each other and A and C know each other, its is not necessary that b and C know each other.

Zeroth law allows us to introduce the concept of temperature to measure the hotness of coldness of body. All bodies in thermal equilibrium are assigned equal temperature. A hotter body is assigned higher temperature then colder body. Thus, the temperature of two bodies decides the direction of heat flow when the two bodies are put in contact. Heat flows from the body at higher temperature to the body at lower temperature.

Example question

A system X is neither in thermal equilibrium with Y nor With Z, The systems y and Z

(1) Must be in thermal equilibrium

(2) Can not be in thermal equilibrium

(3) May be in thermal equilibrium

Solution (3) may be in thermal equilibrium