# Thermal Equilibrium - Objective Question 1

Objective Question:
2 iron blocks, P and Q are in thermal contact. The initial temperature of P and Q are 10°C and 50°C respectively. Which of the followings is true when P and Q are at thermal equilibrium.

1. The temperature of P will be higher than the temperature of Q.
2. The net flow of heat between P and Q is zero
3. The temperature of P and Q will be lower than 50°C but higher than 10°C.
4. There is no heat flow between the 2 blocks.

Answer:
The correct answer is II and III.

Answer I. is incorrect.
When 2 objects achieve thermal equilibrium, the temperature of the 2 objects will be the same.

Answer II. is correct.
When 2 objects achieve thermal equilibrium, the rate of flow of heat is equal, hence there is no net flow of heat between the 2 objects.

Answer III. is correct.
When P and Q are in thermal contact, the temperature of P (10°C)will increase whereas the temperature of Q (50°C) will decrease. When P and Q are in thermal equilibrium the temperature of P and Q will be the same and the temperature will be higher than 10°C but lower than 50°C.

Answer IV. is incorrect.
In thermal equilibrium, there is still heat flow between P and Q.

However, the rate of the heat flow is equal in both direction (P to Q and Q to P), hence the net flow of heat between P and Q is zero.