18WuD2x

electromagnetic energy conversion • electromagnetic microphone 241
and vice versa, through the intermediary of an
electromagnetic field.
electromagnetic environment A region in which
electric and magnetic fields are present.
electromagnetic field A combination of alternating
electric and magnetic fields. The electric lines
of flux are perpendicular to the magnetic lines of
flux at every point in space. The field propagates
in a direction perpendicular to both the electric
and magnetic lines of flux. The frequency of oscillation
can range from a fraction of one Hz to many
quadrillions of Hz. In order from longest wavelength
(lowest frequency) to shortest wavelength
(highest frequency), effects of this type include radio
waves, infrared, visible light, ultraviolet,
X rays, and gamma rays.
Control grid
Cathode
Cross section of
focusing coil
Lines of force bend
electron streams
inward so that they
converge at the
screen
Beam
electromagnetic focusing
Wavelength
(meters)
Screen
Magnetic
field
Electric field
10 −16
10 −14
10 −12 Gamma rays
10 −10 X rays
10 −8 Ultraviolet rays
10 −6 Infrared
10 −4 Microwaves
10 −2 FM broadcast short waves
1 AM broadcast
10 2
10 4
10 6 60 Hz alternating current
10 8
Direction
of propagation
electromagnetic field
electromagnetic flux The magnetic field surrounding
a coil or conductor carrying an electric
current.
electromagnetic focusing In a television picture
tube, electron-beam focusing obtained by varying
the direct current flowing through an external
focusing coil.
electromagnetic force The force that causes a
conductor to be displaced from its position in a
magnetic field when it conducts current.
electromagnetic frequency spectrum The frequency
range of electromagnetic fields including
radio waves, infrared, visible light, ultraviolet,
X rays, and gamma rays. Ranges from a fraction
of one Hz to many quadrillions of Hz.
electromagnetic horn radiator A horn used to radiate
microwave energy. Also see HORN AN-
TENNA.
electromagnetic induction Inducing a voltage in
a circuit or conductor by causing alternating
current to flow in another nearby circuit or con-
electromagnetic frequency spectrum
ductor. Compare ELECTROSTATIC INDUC-
TION.
electromagnetic inertia The tendency for the current
in a circuit to lag the voltage at high frequencies.
electromagnetic interference Abbreviation, EMI.
A phenomenon in which electronic devices upset
each other’s operation. Computers, television receivers,
telephone sets, high-fidelity sound
equipment, and certain medical devices can
malfunction because of strong radio-frequency
fields such as those from a nearby broadcast
transmitter. The EMI is usually the result of
improper or ineffective shielding in the affected
device or system.
electromagnetic lens A coil or coil system whose
magnetic field causes an electron beam passing
through it to converge or diverge as a light beam
does in passing through an optical lens. Compare
ELECTROSTATIC LENS. Also see ELECTROMAG-
NETIC FOCUSING.
electromagnetic mass The mass that a moving
electric charge is thought to possess.
electromagnetic microphone A microphone in
which sound energy is converted into proportionate
electrical energy by electromagnetism. Common