Micro waves (short wavelength radio waves ), with frequencies in the gigahertz(GHz)range, are produced by special vaccum tubes (called klystrons, magnetrons and gunn diodes). Due to their short wavelength they are suitable for the Radar Systems used in air crafts navigation .
Radar also provides the basis for the speed guns used to time fast balls , tennis-server, and automobiles . Microwave ovens are an intresting domestic applications of these waves. In such ovens , the frequency of the microwave is selected to match the resonant frequency of water molecules so that energy from the waves are transferred efficiently to the kinetic energy of the molecules . This raises the temperature of any food containing water.
