【正文】 the shortest waves, those of gamma radiation, result from changes within the nucleus of the atom. In order of decreasing wavelength and increasing frequency, various types of electromagic radiation include: electric waves, radio waves (including AM, FM, TV, and shortwaves), microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma radiation. According to the quantum theory, light and other forms of electromagic radiation may at times exhibit properties like those of particles in their interaction with matter. (Conversely, particles sometimes exhibit wavelike properties.) The individual quantum of electromagic radiation is known as the photon and is symbolized by the Greek letter gamma. Quantum effects are most pronounced for the higher frequencies, such as gamma rays, and are usually negligible for radio waves at the longwavelength, lowfrequency end of the spectrum. 。 they are alike in all other respects. The possible sources of electromagic radiation are directly related to wavelength: long radio waves are produced by large antennas such as those used by broadcasting stations。 109 or 1 billion cycles per second.) Wavelength (represented by the symbol λ, the Greek letter lambda) is the distance between a crest and the adjacent crest, or a trough and an adjacent trough, of a wave. The higher the frequency, the shorter the wavelength. Amplitude, though mathematically independent from the parameters discussed, is critical to the understanding of sound. Defined as the maximum displacement of a vibrating material, amplitude is the size of a wave. The greater the amplitude, the greater the energy the wave contains: amplitude indicates intensity, which, in the case of sound waves, is manifested as what people monly call volume. Similarly, the amplitude of a light wave determines the intensity of the light. electromagic radiation,energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magic field, and if the motion is changing (accelerated), then the magic field varies and in turn produces an electric field. These interacting electric and magic fields are at right angles to one another and also to the direction of propagation of the energy. Thus, an electromagic wave is a transverse wave. If the direction of the electric field is constant, the wave is said to be polarized (see polarization of light). Electromagic radiation does not require a material medium and can travel through a vacuum. The theory of electromagic radiation was developed by James Clerk Maxwell and published in 1865. He showed that the speed of propagation of electromagic radiation should be identical with that of light, about 186,000 mi (300,000 km) per sec. Subsequent experiments by Heinrich Hertz verified Maxwell39。 106 or 1 million cycles per second)。 103 or 1,000 cycles per second)。 superconductivity. Almost everyone has experienced the Doppler effect, though perhaps without knowing what causes it. For example, if one is standing on a street corner and an ambulance approaches with its siren blaring, the sound of the siren steadily gains in pitch as it es closer. Then, as it passes, the pitch suddenly lowers perceptibly. This is an example of the Doppler effect: the change in the observed frequency of a wave when the source of the wave is moving with respect to the observer. The Doppler effect, which occurs both i