In Schroeder's An Introduction to Thermal Physics, heat is defined as the "spontaneous flow of energy from one object to another" and work is defined thermodynamically as any other transfer of energy into or out of a system.
Schroeder then goes on to say
"The definitions of heat and work are not easy to internalize, because both of these words have very different meanings in everyday language. It is strange to think that there is no "heat" entering your hands when you rub them together to warm them up, or entering a cup of tea that you are warming in the microwave. Nevertheless both of these processes are classified as work, not heat."
However, Schroeder goes on to say that there are three processes of heat transfer: conduction, convection, and radiation.
Is heating an object in a microwave not an example of radiation? It is not obvious to me why this process is considered work and not heat. Is it because the process of starting the microwave is not spontaneous? And if so, why is this process not spontaneous?
Also, what is happening at a micro level here. To me, it seems like the food is being heated in two ways. First, some of the energy from the radiation in the microwave is heating the air molecules, which are themselves heating the food by conduction. Second, some of the energy from the radiation of the microwave is not being absorbed by the air molecules but is instead directly being absorbed by the food. Is this accurate?
