We have used the example of a taut string to explore the physical characteristics
of standing waves. However, standing waves occur in many different physical
situations and the ideas we have been discussing are important to a wide range of
physical phenomena. In a microwave oven, electromagnetic waves reflect from the
walls of the oven to form standing wave patterns in the oven compartment. This
means that there will inevitably be places in the compartment where the intensity
of the microwave radiation is reduced and the food will not be properly cooked. To
reduce the effects of these ‘cold spots’ the food is placed on a rotating turntable. In
a laser, the light forms a standing wave between the two mirrors placed at the ends
of the laser tube. In this way the wavelength of the laser light is well defined, i.e.
monochromatic. In a very different example, in the realm of quantum mechanics,
the discrete energy levels of atoms can be thought of as the standing-wave solutions
of the Schr¨odinger equation.