Thermal physics (CH19)

A2 thermal physics definitions and rules

Name the ways of transferring energy to or from an object.

• by heating

• by work done

What is conduction?

When one neighbouring particle transfer the heat (thermal energy) to another neighbouring particle

(this usually takes time)

What is convection?

When the energy is transferred in a ‘flow’ instead of layer-by-layer. This can only happen in fluids (liquids and gases). It does not wait for each ‘layer’ like conduction.

What is radiation?

The emission of infrared light (waves)

What is work done by a force?

Mechanical work, W = F x d(cosθ)

What is work done by an electric current?

W = VIt

What is internal energy?

The sum of random distribution of the kinetic and potential energies of all an object’s particles.

What is meant by random distribution?

x

What is thermal energy? And temperature?

The energy of an object due to its temperature. Temperature is a measure of how much an object’s particles move.

What happens in order for the internal energy of an object to be constant?

The rate of energy transfer to the object is the same as the rate of energy transfer away from the object.

What is specific latent heat (of vaporisation)?

The energy required to change the state of a substance (by condensing or boiling) without changing its temperature

What is specific latent heat (of fusion)?

The energy required to change the state of a substance (by freezing or melting) without changing its temperature

What is specific heat capacity?

The amount of energy required to raise the temperature of 1kg of a substance by 1 degree, without changing state.

Name some common assumptions when energy is being transferred to/from objects.

• constant rate of energy transfer (heat loss/gain)

• object remains at the same temperature

• object does not change state

• no energy is transferred to or from the surroundings

What is the main theme of this topic?

The conservation of energy. So always make equations that CONSERVE energy; Et = E1 + E2

Equation for work done in expanding.

W = p x (change in) Volume