Question

how does a pressure cooker works and save the energy?

Answer 1

working proces of a pressure cooker.

Answer 2

This is because the difference between the pressure cooker and normal cooker is that in a pressure cooker the heat is retained so the food is cook faster saving LPG and heat energy hence the energy is saved, but in a normal cooker this does not happen as it cannot retain the heat energy.
eg : the evolution of bulb happened to saved heat energy as a bulb waste a lot of energy CFL save some of it and LED save a lot of heat energy