If we want to describe work , we must have what ?

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.

The voltage applied across a given parallel-plate capacitor is doubled. how is the energy stored in the capacitor affected?

Which wave is the result of amplification and produces a louder sound