B.1.7—Thermal transfer direction

Temperature difference drives net transfer

When two bodies at different temperatures can exchange energy, the net thermal energy transfer is from the higher-temperature body to the lower-temperature body.

What equilibrium means

Transfer can occur in both directions microscopically, but at thermal equilibrium the opposing transfers balance and there is no net transfer. Equal temperature is the condition for zero net thermal transfer, not necessarily equal internal energy.

Apply the direction rule

First compare temperatures, then draw the net energy arrow. The arrow is independent of which object is heavier or contains more total internal energy.

Common trap

A larger object can contain more internal energy while still receiving energy from a smaller, hotter object. “Hotter” means higher temperature, not “more total energy”.

How it is assessed

The evidence asks why a heated block approaches a constant temperature and rewards a link between heat loss and heater power.

Command terms

Suggest / Explain

What earns marks

State that net thermal transfer is from higher temperature to lower temperature. For a body approaching a constant temperature, explain the energy balance: heater power in equals thermal energy loss to the surroundings, so the net rate of internal-energy increase approaches zero. Do not write “thermal equilibrium” without this balance.

Watch for

Saying only “thermal equilibrium” without explaining equal energy-in and energy-out rates.

Representative question

[Maximum number: 2]

Suggest why the temperature of the block approaches a constant value.

B.1.7—Thermal transfer direction

Predict the Direction of Thermal Energy Transfer

B.1.7 Exam Analysis

Assessment in practice

Question 1