Work Done by a Gas (AQA A Level Physics): Revision Note

Work done by a gas

• When a gas expands, it does work on its surroundings by exerting pressure on the walls of its container

  • This is important, for example, in a steam engine where expanding steam pushes a piston to turn the engine

• The work done when a volume of gas changes at constant pressure is defined as:

$W=p∆V$

• Where:

  • $W$ = work done (J)

  • $p$ = pressure of gas in piston (Pa)

  • $∆V$ = change in volume of gas (m³)

• This is assuming that the pressure of the gas in the piston $p$ does not change as the gas expands

• When the gas expands ($V$ increases), work is done by the gas

• When the gas is compressed ($V$ decreases), work is done on the gas

• For a gas inside a cylinder enclosed by a moveable piston, the force exerted by the gas pushes the piston outwards

• Therefore, the gas does work on the piston