**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.

- The temperature of P will be higher than the temperature of Q.
- The net flow of heat between P and Q is zero
- The temperature of P and Q will be lower than 50°C but higher than 10°C.
- 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.