Question

The Zeroth Law of Thermodynamics provides the basis for temperature measurement. If Body A is in thermal equilibrium with Body B, and Body B is in thermal equilibrium with Body C, which property must be identical for all three?

• A. Internal Energy (U)
• B. Total Enthalpy (H)
• C. Temperature (T)
• D. The product of Pressure and Volume (PV)

Hint:

The Zeroth Law is the mathematical justification for using thermometers.
If a thermometer ($B$) reads the same value for body $A$ and body $C$, then $A$ and $C$ are at the same temperature.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question tests the fundamental definition and physical significance of the Zeroth Law of Thermodynamics.
This law establishes a transitive relation for thermal equilibrium, which allows us to define and measure temperature.

Step 2: Key Formula or Approach:
The Zeroth Law states:
If system $A$ is in thermal equilibrium with system $B$, and system $B$ is in thermal equilibrium with system $C$, then system $A$ is in thermal equilibrium with system $C$.

Step 3: Detailed Explanation:

• Thermal Equilibrium: When two systems are in thermal equilibrium, there is no net flow of thermal energy (heat) between them when they are connected by a path permeable to heat.

• The physical parameter that determines whether heat will flow between systems is temperature.

• Therefore, systems in thermal equilibrium must share the same value of this state variable, which is temperature ($T$).

• Other properties like internal energy ($U$), enthalpy ($H$), or the product $PV$ depend on the mass, volume, and chemical nature of the substance, and do not need to be equal for systems to be in thermal equilibrium.

Step 4: Final Answer:
The property that must be identical for all three bodies is Temperature ($T$).