18WuD2x

width modulation • Wilson cloud chamber 751
C S
width modulation Modulation of the interval during
Wien-bridge heterodyne eliminator A notch filter
which a gate circuit is open.
composed of a continuously variable Wien-bridge
Wiedemann effect See DIRECT WIEDEMANN EF- circuit (see WIEN BRIDGE). The device is connected
FECT.
in the audio-frequency channel of a radio
Wiedemann-Franz law For metals that are good receiver, and is tuned to remove a troublesome
electrical conductors, the ratio of thermal conductivity
to electrical conductivity is nearly constant,
heterodyne whistle.
Wien-bridge oscillator An oscillator in which the
and is proportional to the absolute
temperature.
frequency-selective feedback network is a Wienbridge
circuit (see WIEN BRIDGE). Also see
Wien bridge A frequency-sensitive bridge in which BRIDGE-TYPE OSCILLATOR.
two adjacent arms are resistances and the other
two adjacent arms are resistance-capacitance
(RC) combinations. One of the latter contains resistance
and capacitance in series; the other con-
C5
C4
tains resistance and capacitance in parallel.
C1
Because the bridge can be balanced at only one R1
R2
C3
Output
frequency at a time, it is useful as a simple audio
R4 R7
C2
R5
frequency meter (see BRIDGE-TYPE AF METER).
It is used also for capacitance and resistance R3 LP1
R6
measurements. When inductors are substituted
+B +B
C X portional to the absolute temperature.
for the capacitors, the Wien bridge can be used
for inductance measurements (see WIEN INDUC-
TANCE BRIDGE).
Wien-bridge oscillator
Gen
Wien capacitance bridge A Wien bridge arranged
for the measurement of unknown capacitance.
Wien effect For an electrolytic substance, an increase
in conductivity (decrease in resistivity)
R 1 R 2
that occurs when a very large voltage is placed
across the material. This voltage must be greater
than approximately 1 megavolt per 50 cm.
Det
Wien inductance bridge A Wien bridge containing
inductors in place of capacitors and used for the
R 3 R 4
measurement of unknown inductance.
Wien’s displacement law The wavelength of maximum
radiation of a black body is inversely pro-
Wien’s first law See WIEN’S DISPLACEMENT
Wien bridge
LAW.
Wien’s laws See WIEN’S FIRST LAW, WIEN’S
SECOND LAW, and WIEN’S THIRD LAW.
Wien’s radiation law See WIEN’S SECOND LAW.
Wien-bridge audio frequency meter See WIEN- Wien’s second law The emissive power of a black
BRIDGE FREQUENCY METER.
body is proportional to the fifth power of the absolute
Wien-bridge distortion meter A distortion meter
temperature.
in which a Wien bridge circuit is used to remove Wien’s third law An empirical law for the spectral
the fundamental frequency from the complex
waveform. The bridge is inserted between amplifier
stages, and its notch response is sharpened
by means of overall negative feedback.
Wien-bridge equivalent A resistance-capacitance
null circuit, such as the parallel-tee (twin-tee)
network, which has the same balance equation as
the Wien bridge.
Wien-bridge filter A Wien bridge used as a bandsuppression
filter (notch circuit).
Wien-bridge frequency meter A bridge-type audio
frequency meter in which the continuously variable
frequency-selective circuit is a Wien bridge.
Also see BRIDGE-TYPE AF METER.
distribution of energy radiated from a black body
at a specified temperature. The distribution is a
curve with a peak (maximum) at a wavelength
that depends on the temperature. The higher the
temperature, the shorter the wavelength at which
maximum radiation occurs.
willemite See ZINC ORTHOSILICATE PHOSPHOR
and ZINC SILICATE PHOSPHOR.
Williams tube A type of electrostatic cathode-ray
storage tube.
Wilson chamber See WILSON CLOUD CHAMBER.
Wilson cloud chamber An airtight chamber containing
water vapor or alcohol vapor at low pressure,
and provided with a viewing window.