GLOSSARY
AC voltage: A potential
difference that not only changes magnitude in time but also changes
polarity in time. The change is usually sinusoidal but can be square or
triangular.
ammeter: An instrument
that measures current in amperes (amps). An ammeter must be connected
in series with the device through which it measures the current.
ampere: The unit of
current in the SI system.
amplifier: A device
capable of increasing (or decreasing) a potential difference.
amplitude: The maximum
displacement of a periodic oscillation from its equilibrium state.
banana plug: A common type of
plug shaped like a banana.
bias: Refers to the polarity of
an applied voltage.
BNC: Berkeley Nucleonics
Corporation. A standard plug/jack combination that makes a positive and
secure connection.
capacitor: A device that
stores charge and therefore electrical
energy.
characteristic curve: The
name of a graph of the current vs. voltage of a given circuit element.
The current is on the y-axis and the voltage is on the x-axis so the
slope of the curve at any given point gives the reciprocal of the
resistance of the element {from Ohm's law: I = (1/R)V}.
charge: That fundamental
quantity a body possesses that measures the body's magnitude of
electrical interaction.
coaxial cable: A shielded
wire where one wire is braided over the other such that their
lengthwise axis are parallel.
AC coupling: Allows AC and DC
signals to exist simultaneously (or not) in a scope display. This
o-scope feature can be used to filter unwanted DC signals from the
input signal and allow only the AC signal to be displayed.
current: Electric charge
that flows with time. Note, current doesn't flow, charge flows.
discrepancy test: Also
called a "percent difference", this value is computed by taking
measurement A and subtracting from it measurement B and dividing this
by the "real" or theoretically correct or if nothing else the smaller
of the two. Multiplying by 100% (i.e., 100/100) is optional and
expresses the result as a percent rather than as a ratio.
DC offset: The amount of
constant voltage added to any AC signal. Dc offset can be negative or
positive.
DC voltage: Voltage that
does not change its polarity over time. Although some definitions
include a voltage that doesn't change in any way over time.
diode: A diode is a PN junction
whose function in a circuit allows charge to flow through it in one
direction only.
DMM: Digital Multi-meter.
A measurement device similar to a VOM except that its output is digital
rather than analog.
Electric Potential: The
electric potential at a point is defined to be equal to the amount of
work done by an external force to move a charge from infinity to the
point in question at constant kinetic energy divided by that same
amount of charge (V = W/q).
EMF: Electro-motive force.
Strictly, the emf of a source of electric potential energy is defined
as the amount of electric energy delivered by the source per couloumb
of positive charge as this charge passes through the source from the
low potential terminal to the high potential terminal. Often this
simply may refer to the terminal voltage of a battery.
farad: The unit of
capacitance.
frequency: The amount of
cycles an oscillation makes in one second.
function generator: An
instrument that outputs an AC voltage signal in a variety of forms,
frequencies and peak to peak voltage (amplitude). A DC offset may also
be available.
gain: The amount of
amplification of a given input signal.
ground potential: Or just
"ground". That electric potential equal to the earth's. Assigned the
value of zero volts.
henry: The unit of
measure of inductance.
hertz: The unit of measure of
frequency. One hertz is equal to one cycle per second.
impedance: The opposition
to current that is produced by joule resistance and reactance.
inductor: A coil of wire
used for its magnetic effects in AC circuits.
jack: What a plug goes
into.
Kirchoff's rules: Two
rules that express charge conservation and energy conservation in a
circuit.
Lissajous figure: Highly
symmetric figures usually seen on an oscilloscope screen under certain
condition.
Magnetic Flux: That amount of
magnetic field that passes through a surface in a direction
perpendicular to the surface, multiplied by the area of that same
surface.
ohm: The unit of
resistance.
Ohms' law: A
non-fundamental quantitative relation between voltage, current and
resistance. Although commonly written
V = IR, it is preferred to be written as I = V/R since conceptually we
think of the current as dependent on the voltage that creates it.
oscilloscope: An
instrument that measures the voltage of an input signal as a function
of time and displays it on the face of a cathode ray tube.
parallel: One of two
basic ways to connect circuit elements. Specifically, two elements are
connected in parallel when the voltage across each of them is
necessarily the same.
peak to peak: Refers to
the difference between the highest value and the lowest value of a
signal.
period: The time it takes a
periodically varying value (or signal) to complete on full cycle of
oscillation.
phase: Refers to the value of a
periodic signal when t=0.
plug: The male connector of a
jack-plug system.
PN junction: A solid-state
construction that allows the control of the flow of charge.
potential difference: A
difference in potential is the definition of voltage.
power supply: A device that
supplies a voltage and current to a circuit.
RC circuit: A circuit that has
a resistor and a capacitor in it.
RCL circuit: A circuit that has
a resistor, a capacitor and an inductor in it.
reactance: The AC resistance
associated with either a capacitor or inductor. Related to but not to
be confused with impedance.
rectify: To change an AC signal
to a DC signal.
resistance: That property of a
circuit element that resists the flow of charge through itself and
consequently generates heat.
RMS: Root-Mean-Square. The
square root of the average of a quantity squared.
sawtooth: A type of time
varying voltage that has the appearance of a tooth from a saw blade.
series: A connection such that
the flow of charge is necessarily the same through each element.
short circuit: A circuit of
zero resistance where, usually by accident, an element has been
eliminated from a circuit by a wire of very low resistance is connected
across the element.
signal: Any type of voltage
(time varying or not) that drives a circuit or is capable of driving a
circuit. Also the word signal may refer to the input voltage to a
measuring device.
sinusoid: A type of
time-varying signal that oscillates harmonically.
square: A type of time-varying
signal that changes from one value to another value instantly. A square
signal has only two different values that oscillate between one another.
time base: The device on an
oscilloscope that controls the horizontal motion of the beam allowing
the beam to sweep out equal distances over equal intervals of time.
time constant (τ): A useful
parameter in RC and LR circuits. The time constant is defined to be
equal to the time it takes for the voltage across an element to
decrease to 1/e of its initial value.
trace: The path of light
emitted by the phosphors on the face of the CRT on an oscilloscope as
the electron beam sweeps across it.
trigger: Sets the voltage at
which the trace starts sweeping.
volt: The unit of electric
potential or voltage in the SI system.
voltage: A difference in
electric potential between two points in space or in a circuit.
VOM: Volt-Ohm-Meter. An analog
measuring tool that measure voltage, current or resistance.
wave: A non-equilibrium
disturbance that propagates through an elastic medium. NOT WHAT YOU SEE
ON YOUR OSCILLOSCOPE SCREEN!
waveform: Refers to the shape
of one complete cycle of a periodic input signal as seen from the trace
on the oscilloscope screen. A wavefrom may be sinusoidal, square,
triangle or any other
shape.