Electromagnetic energy is carried at low frequencies in electrons. The energy supplied by electrons is determined by the voltage (the force acting to push electrons through a conductor) and the flow of electrons, known as current. Current flow is measured in amperes or milliamperes (mA). Common residential and industrial machinery uses alternating current, indicating that the flow of electrons alternates in direction, typically at a frequency of 60 cycles per second, or 60 hertz (Hz). A battery, in contrast, supplies direct current, indicating that the flow of electrons proceeds in only one direction.
When the frequency of alternation of current flow is high, the electromagnetic energy can escape its conductor and radiate into space, traveling at the speed of light. Here the energy is carried by photons rather than electrons. The behavior and properties of this electromagnetic energy are determined largely by its frequency. The electromagnetic spectrum includes, in order of increasing frequency, radio waves, microwaves, infrared (heat) radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
X-rays and gamma rays have extremely high frequency and energy content. As a result, this radiation can strike molecules in the body, knocking away electrons and leaving a damaged, electrically charged (i.e., ionized) remnant. Ionized molecules raise the risk of subsequent mutations and cancer. Accordingly, such high-frequency radiation is termed ionizing radiation and has been associated with increased cancer risk. Lower frequency radiation, such as radio waves, visible light, and microwaves, does not cause ionization, and is termed nonionizing radiation. Damage from nonionizing radiation is usually due to simple heating of tissues.
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