A* Summary notes with for 3.6.2.1 Thermal energy transfer, A level Physics.

Thermal Energy Transfer
Internal Energy
Internal Energy (U) = The sum of the randomly distributed
kinetic energies and potential energies of all of the particles
in a body.


Kinetic Energy comes from the speed of the molecules (1/2 x
mv^2).
Potential energy comes from the separation of the molecules.


Gasses have the highest internal energy compared to solids which
have the lowest.




Thermal Energy Transfer 1

, Changing internal energy

Increase Decrease

Doing work on it Changing state (melting or
evaporating)
Heating it up (increasing
the kinetic energy of the Cooling down
molecules)




First Law of Thermodynamics:
The internal energy of a system is increased when
energy is transferred to it by heating or when
work is done on it.

- This law is applicable in all situations, not just gasses.


Examples

When a gas expands its internal energy decreases because
the gas has had to do work on the surroundings.

When a gas is compressed its internal energy increases
because the work has been done on the gas by the
surroundings




Thermal Energy Transfer 2