Question

How are microwaves produced ? Why is it necessary in microwave ovens to select the frequency of microwaves to match the resonant frequency of water molecules ?

Answer 1

Microwaves are produced by vacuum tubes devices that operate on the ballistic motion of electron controlled by magnetic or electric fields. Some different kinds of microwave emitters are the cavity magnetron, the klystron, the traveling-wave tube(TWT), the gyrotron and all stars. These devices work in the density modulated mode, instead of current modulated mode, meaning that they work on the basis of clumps of electrons flying ballistically through them, instead of using a constant flow of electrons. Lower power microwaves can me produced by some solid state devices such as the FET (field effect transistor), the tunnel diode, the gunn diode, and the IMPATT diode.

Microwaves are used in microwave ovens for cooking and keeping the food fresh. In such ovens the frequency of microwave is selected to match the resonant frequency of water molecules so that energy from these waves is transferred efficiently as kinetic energy of water molecules which is shared by the entire food without any waste of energy