Question

According to Zeroth law of thermodynamics, if two systems $A$ and $B$ are separately in equilibrium with $C$, then

• A. $T_{A}=T_{B}$
• B. $T_{A}>T_{C}, T_{B}>T_{C}$ and $T_{A}=T_{B}$
• C. $T_{A}=T_{C}$ and $T_{A} \neq T_{B}$
• D. $T_{A} < T_{C}, T_{B} < T_{C}$ and $T_{A} = T_{B}$

Answer 1

Answer: (A)

According to Zeroth law of thermodynamics, two systems in thermal equilibrium with a third system separately are in thermal equilibrium with each other.
So, if $A$ and $B$ are separately in equilibrium with $C$, then $T_{A}=T_{C}$ and $T_{B}=T_{C}$.
This implies that $T_{A}=T_{B}$, i.e. the systems $A$ and $B$ are also in thermal equilibrium.