Which physical property does the zeroth law of thermodynamics allow us to define?

• A. Temperature
• B. Pressure
• C. Internal energy
• D. Entropy

Answer: (A)

Verified step by step guidance

1. Understand the statement of the zeroth law of thermodynamics: It states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
2. Recognize that thermal equilibrium means no net heat flow occurs between systems, implying they share a common physical property.
3. Identify that the physical property shared by systems in thermal equilibrium is temperature, which can be used to compare and define thermal states.
4. Note that the zeroth law provides the fundamental basis for the concept of temperature, allowing us to use thermometers to measure it.
5. Conclude that among the options given, the zeroth law specifically allows us to define temperature, not pressure, internal energy, or entropy.