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 (): 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 voltage in the SI system.

voltage: A difference in electric potential between two points in space or in a circuit.

VOM: Volt-Ohm-Meter. A common analog measuring tool that measure volts, amps 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.