Conduction is like a line of people passing a hot ball from one hand to the next.
When you put a pan on a stove, the heat from the burner travels through the metal by conduction, making the pan hot enough to cook your food.
The speed of this transfer depends on the metal’s thermal conductivity (\$k\$).
The basic formula is:
| Symbol | Meaning |
|---|---|
| \$Q\$ | Heat transferred (J) |
| \$k\$ | Thermal conductivity (W m⁻¹ K⁻¹) |
| \$A\$ | Area of contact (m²) |
| \$\Delta T\$ | Temperature difference (K) |
| \$L\$ | Thickness of material (m) |
Exam Tip: When asked to calculate heat transfer, identify \$k\$, \$A\$, \$\Delta T\$, and \$L\$ from the question.
Remember that a higher \$k\$ means faster conduction – think of aluminium as a super‑fast runner compared to wood.
Convection is like a dance where warm air rises and cool air falls, creating a cycle.
In a room, a heater warms the air near it. That warm air expands, becomes less dense, and rises.
Cooler air then moves in to replace it, gets heated, and the cycle repeats.
This process can be described by the equation for convective heat transfer:
| Symbol | Meaning |
|---|---|
| \$Q\$ | Heat transferred (J) |
| \$h\$ | Convective heat transfer coefficient (W m⁻² K⁻¹) |
| \$A\$ | Surface area of the heater (m²) |
| \$\Delta T\$ | Temperature difference between heater surface and air (K) |
Exam Tip: Convection is often the dominant mode in indoor heating.
When you see a question about a room being heated, think about the air flow pattern and use the \$h\$ value given or estimate it from the problem context.
Remember that \$h\$ can vary with the type of heater (radiator, fan, etc.).
Radiation is like a superhero that can travel through empty space.
The Sun’s rays reach Earth via radiation, warming the planet even though there’s no air in space.
Other everyday examples:
Exam Tip: Radiation follows the Stefan–Boltzmann law: \$P = \varepsilon \sigma A T^4\$.
When asked to compare radiative heat loss from two surfaces, check their emissivity (\$\varepsilon\$) and temperature.
A higher \$\varepsilon\$ or \$T\$ means more radiation.