Q.Three metal blocks A, B and C are brought into contact. Block A is found to be in thermal equilibrium with block B, and block B is separately found to be in thermal equilibrium with block C. Using the Zeroth Law of Thermodynamics, what can you conclude about blocks A and C? Explain how this justifies the use of a thermometer.

[!TLDR] The Zeroth Law states that two systems each in thermal equilibrium with a third system are in thermal equilibrium with each other. [!ANSWER] Blocks A and C must also be in thermal equilibrium with each other, even tho …

The Zeroth Law of Thermodynamics states that if system A is in thermal equilibrium with system C, and system B is separately in thermal equilibrium with system C, then A and B must also be in thermal equilibrium with each other. Applying this directly to the given scenario (with B playing the role of the common reference system, connecting A and C): since A is in thermal equilibrium with B, and B is in thermal equilibrium with C, the Zeroth Law lets us conclude that A and C are in thermal equilibrium with each other too — without A and C ever needing to be placed in direct physical contact. This is exactly the principle that justifies using a thermometer: the thermometer plays the role of the common reference system (like B here). If a thermometer reaches thermal equilibrium with object A and reads a certain temperature, and is then separately brought into equilibrium with object C and reads the …

State the Zeroth Law, then map the given blocks onto system A, system B (the common reference), and system C to draw the conclusion, finally …

Concluding A and C are equal WITHOUT invoking the Zeroth Law explicitly; failing to connect the result to wh …