Thermal physics

Conduction, convection and radiation, and specific heat capacity calculations.

6 min read

Conduction: energy passes through a solid as particles vibrate and pass energy on. Metals conduct best (free electrons); rate rises with temperature difference and depends on the material and its thickness.
Convection: in fluids, heated regions become less dense and rise while cooler fluid sinks, setting up a convection current.
Radiation: thermal energy as infrared electromagnetic waves; no medium is needed. Dark, matt surfaces absorb and emit best; shiny, light ones least.

The specific heat capacity $c$ is the energy to raise $1 kg$ by $1° C$ : $c = \frac{thermal energy}{mass \times temperature change}$ , so energy $= m c Δ θ$ (units J kg⁻¹ °C⁻¹).

Worked example

How much energy raises $2 kg$ of water ( $c = 4200$ ) by $30° C$ ?

$E = m c Δ θ = 2 \times 4200 \times 30 = 252000 J .$

Saying radiation needs a medium (it travels through a vacuum).
Forgetting that convection happens in fluids (liquids and gases), not solids.
Using temperature instead of temperature *change* in $m c Δ θ$ .

Thermal physics

Heat transfer

Specific heat capacity

Common mistakes