external and internal pressures

[505706331]

hi can someone please explain the key points of external and internal pressures? is internal pressure what is going on inside a beaker? I'm a little confused about external pressure

[Anna Dai-Liu 3B]

External pressure is the pressure that any expansion of the gas inside will work against. It's basically the pressure of the surrounds - whereas internal pressure would be the pressure of the system; a difference in these two may lead to some kind of work done.