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conductor, a voltage is induced in it.
electromagnetic interference. See EMI.
electromagnetic radiation. One method by which energy is transmitted from one location to another.
Radio and television signals, for example, reach us by electromagnetic radiation. When electric and
magnetic fields oscillate back and forth at a high enough frequency, they extend out into space in the form
of waves. These waves may be absorbed (received) at some distant point.
Very little energy transmitted by electromagnetic radiation is lost, or used up, by the space
between the point from which it is sent and the point at which it is received. Energy from the sun reaches
the earth by electromagnetic radiation, and only a very small amount of this energy is lost in the empty
space between the sun and the earth.
electromagnetic vibrator. A device that interrupts a flow of direct current and changes it into pulsating
DC. An electromagnetic vibrator consists of an electrical relay whose contacts are held closed by a spring
and opened by the pull of the electromagnetic coil. The contacts and coil are connected in series across a
source of direct current.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 220
When current flows through the coil, the magnetic field pulls the contacts open and stops the
current. When the current stops flowing, the spring closes the contacts and current begins to flow again.
The contacts vibrate between open and closed as long as the vibrator is connected to a source of direct
current.
electromagnetic waves. Vibrations of electric and magnetic fields that move at the speed of light.
Electromagnetic waves radiate out at right angles to the direction of their wave motion.
electromagnetism. The magnetic field surrounding a current-carrying conductor. The strength of the field
is determined by the amount of current flowing in the conductor.
electromechanical frequency meter. A type of instrument that uses the resonant frequency of a vibrating
metal reed to measure the frequency of alternating current.
Metal reeds having different lengths are vibrated by electromagnetism produced by the alternating
current. The reed whose resonant frequency is the same as that of the AC will vibrate with the greatest
amplitude, and the resonant frequency of this reed is shown on a calibrated scale on the face of the
instrument.
An electromechanical frequency meter is also called a vibrating-reed frequency meter.
electromotive force. See EMF.
electron. The negatively charged part of an atom of which all matter is made. Electrons circle around the
nucleus of an atom in orbits, or shells, and electrons of certain atoms can be forced out of their outer shell
and caused to move from one atom to another to produce a flow called electron current.
electron beam. A thin stream of electrons all moving in the same direction under the influence of electrical
or magnetic fields. Electron beams may be focused and directed by these fields.
When an electron beam strikes certain phosphors, electroluminescence is produced and the
phosphor glows. This is the way the image is formed on a television screen and on the face of a cathode-ray
tube.
electron-beam welding. A method of welding metal by the heat produced when a high-speed stream of
electrons strikes the metal. Electron-beam welding is used in applications in which the heat must be
concentrated at the point the weld is being made.
electron current. The movement of electrons through a circuit from the negative terminal of the power
source to its positive terminal.
Electron current moves in the direction opposite the direction of the arrowheads in the symbol for
a semiconductor diode. These symbols are drawn to follow conventional current, an imaginary flow
considered to be from positive to negative. Electron current is the actual movement of electrons.
electron drift. The relatively slow movement of individual electrons through a conductor. Electron drift is
not the same as electron flow, or electron current.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 221
electronic. Relating to the application of the flow of free electrons through semiconductor devices and
across a vacuum.
electronic emission. The discharge of electrons from a material. Electrons are held tightly in their atoms,
but certain kinds of outside energy can cause them to move from one atom to another.
When heat energy causes electrons to leave, the emission is called thermal emission. When the
electrons are moved out of their atoms by light energy, the emission is called photoemission.
electronic leak detector (air conditioning system servicing tool). An electronic oscillator whose
　
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