How does a basic microwave oven work?

How does a microwave oven work?

• Answer:

  A microwave oven takes advantage of the ability of microwave energy to act on atoms on a molecular level. Take a metal box with a door on it, put in some control electronics, a magnetron (the microwave generating device) and a high voltage power source and you're in business. The user puts an item or items into the cavity (that volume of space where the cooking occurs), and then punches up time and power (often by using preset selections). The high voltage power source powers up the magnetron, and this vacuum tube (a cavity oscillator with its integral magnets) generates microwave energy at about 2.45 GHz. The electromagnetic energy is coupled out of the magnetron, through a waveguide, and into the cavity. In the oven's cavity, the electromagnetic energy acts on electrically polarized molecules in the food. It causes these molecules to move in an attempt to align themselves with the incoming radiation. As the electromagnetic radiation passes molecules, they attempt to align themselves with the magnetic field of that radiation. But the molecules must constantly move to align themselves with the passing magnetic field. The high frequency energy imparts high frequency "torque" to the molecules, and they "flip around" in the passing magnetic field. The energy that the microwaves give molecules is expressed as heat. Water molecules have a relatively high dipole moment, and they react more dramatically to the microwave energy than do the molecules in fats or oils; it is the water molecules in foods that convert the larger part of the microwave energy into thermal energy. The technical term for this kind of thermal stimulation is dielectric heating, but we just use the term "nuc" to describe what we're doing with the oven.