adjacent side The side of a right triangle beside or adjacent to an included angle theta.

algebraic sum All positive quantities in an expression added together and each negative quantity subtractedfrom that result.

alternating current An electrical current which changes in both magnitude and direction.

alternating current generator A device which generates an alternating voltage by rotating a loop of conductor material through a magnetic field.

ammeter A meter connected in series with a circuit, branch, or component which measures the current flowing through that circuit, branch, or component.

ampere The unit of measure for current flow which equals 1 coulomb of electrons passing one point in a circuit in 1 second.

arctangent Inverse of the tangent function. Arctangent of an angle theta means that theta is an angle whose tangent is the arctangent value.

bandwidth The band of frequencies over which ac quantities remain within specified limits. In the case of resonant circuits, it isthe band of frequencies over which the resonant effect exists.

branch Path for current flow in a circuit.

bridge circuit A special type of parallel-series circuit in which the voltages in each branch may be balanced by adjustment of one component. A special version called a Wheatstone bridge may be used to accurately measure resistance.

capacitance The ability of a nonconductor to store a charge. Equal to the quantity of stored charge (Q) divided by the voltage (E) across the device when that charge was stored. Unit of measurement is the farad.

capacitive reactance The changing opposition of a capacitor to the flow of alternating electrical current at the applied frequency. It is inversely related to the source frequency. It is measured in ohms and has the symbol

capacitor A device that can store a charge on conducting plates through the action of an electrostatic field between the plates.

cell A single unit device which converts chemical energy into electrical energy.

chassis A metal frame used to secure and house electrical components and associated circuitry.

circuit A complete path for current flow from one terminal to the other of a source such as a battery or a power supply or an alternating current generator.

circuit analysis A technique of examining components in circuits to determine various values of voltage, current, resistance, power, etc.

circuit reduction A technique of circuit analysis whereby a complex combination of circuit components is replaced by a single equivalent component or several equivalent components.

circuit sense An ability to recognize series or parallel portions of complex circuits to apply series and parallel circuit rules to those portions of the circuit for circuit analysis.

circulating current A characteristic of resonance, it is the larger current in the inductive-capacitive branches of a resonant circuit, the result of the continual charging and discharging of the capacitor and the continual expansion and collapse of the magnetic field of an inductor at the resonant frequency.

coefficient of coupling The fraction of the total magnetic flux lines produced by two coils which is common to both coils.

coil A number of turns of wire wrapped around a core used to oppose changes in current flow. (Also called an inductor.)

combining like terms Algebraic addition of parts of an equation that each contain the same unknown quantity.

common point A voltage reference point in a circuit. A point which is “common” to many components in the circuit.

complex number A number represented by the algebraic sum of a real number and an imaginary number.

condenser See capacitor.

conductance The ability to conduct or carry current. Conductance is equivalent to the reciprocal of (or one over) the resistance.

conductor A material with many free electrons that will carry current.

conjugate of a complex number A complex number with the j-operator having an opposite sign from its mate. For example, the conjugate of 2 + j2 is 2 − j2 and the conjugate of 6 − j4 is 6 + j4.

coulomb A large quantity of electrons that form a unit that is convenient when working with electricity and equals 6.25 billion, billion electrons (or 6.25 ×10¹⁸electrons).

counter electromotive force (CEMF) The voltage that appears across an inductor with a changing current flowing through it due to a property called self-inductance.

current “Electron current” is the flow of electrons (negative charges) through a material from a negative potential to a positive potential. “Conventional current” is the flow of positive charges from a positive potential to negative potential. Current flow is a general term often used to mean either of the above. Symbol is I, unit is ampere.

current magnification The increase in total circuit current caused by the Q factor.

cutoff frequency Specified end frequency points that define bandwidth. In the case of resonance, the frequency at which the effects of resonance fall outside specified limits.

dielectric An insulating material with properties that enable its use between the two plates of a capacitor.

dielectric breakdown (in a capacitor) Failure of an insulator to prevent current flow from one plate of a capacitor through the insulator to the other plate. This often causes permanent damage to the capacitor.

dielectric constant A factor which indicates how much more effective (compared to air) a material is in helping a capacitor store a charge when the insulating material is between the capacitor’s plates.

dielectric strength A factor which indicates how well a dielectric resists breakdown under high voltages.

direct current Current that flows in only one direction. Its magnitude may change but its direction does not.

direct relationship One in which two quantities both increase or both decrease while other factors remain constant.

earth ground A point that is at the potential of the earth or something that is in direct electrical connection with the earth such as water pipes.

effective value Also referred to as rms value. (See root-mean-square value.)

efficiency (of a transformer) The ratio of the power in a secondary circuit divided by the power in a primary circuit.

electricity The flow of electrons through simple materials and devices.

electrolyte A chemical (liquid or paste) which reacts with metals in a cell to produce electricity.

electromagnetic field (magnetic field) field of force produced around a conductor whenever there is current flowing through it. This field can be visualized with magnetic lines of force called magnetic flux.

electromotive force (EMF) A force that makes a current flow in a circuit measured by the amount of work done on a quantity of electricity passing from one point of electrical potential to a higher or lower point of electrical potential. Measured in volts (V).

electron Negatively charged particles surrounding the nucleus of an atom which determine chemical and electrical properties of the atom.

electrostatic force A force which exists between any two charged objects. If the two objects each have the same type of charge, the force is a repulsion. If the two objects each have different types of charge, the force is an attraction. Unlike charges attract; like charges repel.

energy The ability to do work. Unit commonly used in measuring energy is the joule which is equal to the energy supplied by a 1-watt power source in 1 second.

equivalent resistance The value of one single resistor that can be used to replace a more complex connection of several resistors.

exponent A number written above and to the right of another number called the base. Example: 10², 10 is the base, 2 is the exponent. A number which indicates how many times the base is multiplied by itself. 10² = 10 × 10 = 100.

farad The unit of capacitance. A capacitor has 1 farad of capacitance when it can store 1 coulomb of charge with a 1-volt potential difference placed across it.

free electrons Electrons which are not bound to a particular atom but circulate among the atoms of the substance.

galvanometer An ammeter with a center scale value of zero amperes.

giga The metric prefix meaning one billion or 10⁹. Abbreviated G.

graticule The scale on the face of the cathode-ray tube of an oscilloscope.

ground A voltage reference point in a circuit which may be connected to earth ground.

half-power points The upper and lower frequency points of a frequency response curve at which the real power dissipation in the circuit is exactly one-half of what it is at the mid-band frequencies. For resonant circuits the mid-band frequency is the resonant frequencies.

henry Unit of measure for inductance. A 1–henry coil produces 1 volt when the current through it is changing at a rate of 1 ampere per second. Abbreviated H.

horizontal sweep A proportional amount of time required for the spot on the cathode–ray tube face of an oscilloscope to travel from one side of the face to the other side.

hypotenuse The longest side of a right triangle.

imaginary axis Customarily the Y–axis used to represent an imaginary number in a complex number system.

impedance The opposition to the flow of alternating electrical current. The impeding of the current. It is measured in ohms and has the symbol Ω.

inductance The ability of a coil to store energy and oppose changes in current flowing through it. A function of cross sectional area, number of turns on coil, length of coil, and core material.

inductive reactance A quantity that represents the opposition that a given inductance present to a changing ac current in a circuit. It is measured in ohms. It is a direct function of the frequency of the applied ac voltage and the value of the inductor.

inductor A number of turns of wire wrapped around a core used to provide inductance in a circuit.(Also called a coil.)

in–phase Two or more waveforms in which there is a zero–degree phase difference between the waveforms.

instantaneous value The value of voltage or current at a specific instant in the cycle of an ac signal (e.g., a sine wave).

insulator A material with very few free electrons. A nonconductor.

inverse relationship A relationship between two quantities in which an increase in one quantity causes a decrease in the other quantity while other factors are held constant.

junction A connection common to more than two components in a circuit. Also called a node. (See also common point.)

kilo A metric prefix meaning 1,000 or 10³. Abbreviated k.

Kirchhoff’s current law One of many tools of circuit analysis which states that the sum of the currents arriving at any point in a circuit must equal the sum of the currents leaving that point.

Kirchhoff’s voltage law Another tool of circuit analysis which states that the algebraic sum of all the voltages encountered in any loop equals zero.

lagging waveform A waveform whose cycle begins after another waveform cycle.

leading waveform A waveform whose cycle begins before another waveform cycle.

leakage current The small electron flow discharge between plates of a capacitor due to the fact an insulator is not a perfect nonconductor.

leakage resistance The normally high resistance of an insulator such as a dielectric between the plates of a capacitor.

load A device such as a resistor which receives electrical energy from a source and that draws current and/or provides opposition to current, requires voltage, or dissipates power.

loop A closed path for current flow in a circuit.

loop equation The algebraic sum of all the voltages in a loop set equal to zero.

lower cutoff frequency The end frequency point defining the lower end of the bandwidth. For resonant circuits, the frequency below the resonant frequency at which the effect of resonance is outside of specified limits.

magnetic flux Magnetic lines of force in a material.

mega A metric prefix meaning one million or 1,000,000 or 10⁶. Abbreviated M.

micro A metric prefix meaning one millionth or 1/1,000,000 or 10⁻⁶. Abbreviated with the Greek letter mu(μ).

milli A metric prefix meaning one thousandth or 1/1,000 or 10⁻³. Abbreviated m.

mutual inductance A measure of the voltage induced in a coil due to a changing current flowing in another coil close by. Measured in units called henrys (H).

nano A metric prefix meaning one billionth or 1/1,000,000,000 or 10⁻⁹. Abbreviated n.

negative ion An atom which has gained one or more electrons.

node A junction. A connection common to more than two components in a circuit.

node current equations A mathematical expression of Kirchhoff’s current law at a junction or node.

node voltage The voltage at a node with respect to some reference point in the circuit.

non–sinusoidal waveform A waveform that cannot be expressed mathematically by using the sine function.

ohm The unit of resistance. Symbol Ω.

ohmmeter An instrument used to measure resistance.

Ohm’s law A basic tool of circuit analysis which states that, in simple materials, the amount of current through the material varies directly with the applied voltage and varies inversely with the resistance of the material. Gives rise to three common equations for use in circuit analysis: E= IR, R = E/I, I = E/R.

open circuit A circuit interruption that causes an incomplete path for current flow.

opposite side The side of a right triangle across from or opposite to the included angle theta.

oscilloscope An electronic measuring instrument that can visually display rapidly varying electrical signals as a function of time. Often used to measure voltage or current.

out of phase Two or more waveforms in which there is a finite number of degrees of phase difference between the waveforms.

parallel circuit A circuit that has two or more paths (or branches) for current flow.

parallel–series circuit A circuit with several branches wired in parallel. Each branch contains one or more components connected in series, but no single component carries the total circuit current.

peak amplitude The maximum positive or negative deviation of an electrical signal (e.g., sine wave) from a zero reference level.

peak–to–peak amplitude The distance between an ac signal’s maximum positive and maximum negative peaks.

percent A ratio of one part to the total amount. One part of a hundred.

permeability of core material The ability of a material to conduct magnetic lines of force or magnetic flux.

phase The term used to describe the relative position of ac quantities in time reference to each other.

phase angle The angular difference in electrical degrees between the total applied voltage and total current being drawn from the voltage supply in an ac circuit.

phasor A phase vector.

phasor algebra A mathematical method which expresses the value or magnitude of ac quantities such as current, reactance, resistance, or impedance and their respective phase angles, and indicates the phase relationships of these quantities with each other.

phasor diagram A diagram showing the relationships of vectors used to represent phase relationships of ac circuit quantities.

phosphorescence The ability of a material to emit light after being struck with electrons.

pico A metric prefix meaning one million millionth or 10⁻¹². Abbreviated p.

polar coordinators A means of identifying an ac quantity as a vector with a given magnitude (length) and a given direction (phase angle) in a quadrant coordinate system.

polarity of voltage A means of describing a voltage with respect to some reference point, either positive or negative.

positive ion An atom that has lost one or more electrons.

potential difference A measure of force produced between charged objects that moves free electrons. Also called voltage or electromotive force. Symbol is E, unit is the volt (abbreviated V).

power The rate at which work is done or the rate at which heat is generated (abbreviated P). The unit of power is the watt (abbreviated W), which is equal to one joule per second.

power (apparent) A combination of real and reactive power added vectorially, calculated using total current and total voltage values. It is measured in units called volt-amperes (VA).

power (reactive) The product of the voltage across and current through purely reactive circuit components. It is measured in units called volts-amperes-reactive (VAR).

power (real) The power dissipated in purely resistive circuit components. It is measured in units called watts (W).

power dissipated Power which escapes from components in the form of heat by the convection of air moving around the component.

power rating of a resistor (or component) How much power a resistor can dissipate (give off) safely in the form of heat in watts.

power supply A device which is usually plugged into a wall outlet and can replace a battery in many applications by providing a known potential difference between two convenient terminals.

Pythagorean theorem A mathematical theorem describing the relationships between the lengths of the sides of a right triangle: the square of the length of the hypotenuse of a right triangle equals the sum of the squares of the lengths of the other two sides.

quadrant One-fourth of a circle.

quality factor (Q) The ratio of the reactive power in an inductance to the real power dissipated by its internal resistance. It is a measure of the ability of a coil to store energy in its magnetic field and what part of that energy is returned back to the circuit containing the inductance.

radian The angle included within an arc on the circumference equal to the radius of a circle.

rationalization The conversion of the denominator of a fractional number to a real number.

real axis Customarily the X-axis used to represent real numbers in a complex number system.

reciprocal Mathematical “inverse.” The reciprocal of any number is simply that number divided into one.

rectangular coordinates A means of identifying an ac quantity with two numbers which define the location of a specific point on a rectangular X-Y coordinate system.

reference point An arbitrarily chosen point in a circuit to which all other points in the circuit are compared, usually when measuring voltages. Also called reference node.

relay A switch (or combination of switches) activated by an electromagnetic coil.

repetitious waveform A waveform in which each following cycle is identical to the previous cycle.

resistance Opposition to current flow which is a lot like friction because it opposes electron motion and generates heat. Symbol is R. Unit is the ohm (Ω).

resonant frequency A frequency at which a circuit’s inductive reactance and capacitive reactance are the same value. At this frequency the circuit is said to be at resonance.

resultant A vector which represents the sum of two vectors.

root-mean-square The square root of the mean of squared values. Mean is an average of the sum of the squares of instantaneous values of a voltage or current waveform. Root is the square root of the mean. It is abbreviated rms and is sometimes referred to as an effective value.

root-mean-square (rms) value An ac voltage value equivalent to the value of a dc voltage which causes an equal amount of power dissipation due to the circuit current flowing through a resistance. The rms value of a sinusoidal waveform is 70.7 percent or 0.707 of its peak amplitude value. RMS value is also referred to as effective value. It is the effective value of an ac voltage that produces the same amount of resistor power dissipation in heat as a specific dc voltage.

rounding off A procedure by which a number with many digits can be reduced to a number with only a selected number of significant digits. For example, if three significant digit rounding is desired, the first three significant digits are kept, and the fourth examined. If the fourth digit is 5 or greater, the third significant digit is raised by one. If the fourth digit is 4 or less, the first three digits are kept unchanged.

scientific notation A type of shorthand used to keep track of decimal places which utilizes powers of the number 10. Standard form for scientific notation is D.DD × 10^E, where D represents each of the first 3 significant digits, and E represents the exponent, or power of ten.

series circuit A circuit with only one path through which current can flow.

series-parallel circuit A group of series and parallel components in which at least one circuit element lies in series in the path of the total current.

short circuit A path with little or no resistance connected across the terminals of a circuit element.

shunt Another term which means parallel. Often also refers to the low value of parallel resistance used in an ammeter for determining or changing the “range” of the meter.

significant digits Those digits within a number which have the greatest weight. In the decimal system digits to the left of any designated digit are more significant than those to the right.

sign of a voltage A notation, either positive (+) or negative (−), in front of a voltage. (Important in solving circuit equations when analyzing circuits and helps determine the voltage that aids or opposes current flow in a circuit, especially a dc circuit.)

sinusoidal waveform A waveform that can be expressed mathematically by using the sine function. A waveform produced by an alternating current generator which constantly varies in magnitude and direction as determined by the sine trigonometric function.

skin effect The tendency of high frequency current to flow near the surface of a conductor.

solenoid A term used to mean coil or inductor, also used to mean a type of relay such as that used to switch the starter current in an automobile.

source A device, such as a battery or power supply, which supplies the potential difference and electrical energy to the circuit.

square of a number A number multiplied by itself.

square root of a number A number which must be multiplied by itself to obtain the original number.

store A calculator operation where the number in the display is transferred to the memory where it is held until it is recalled. Identified with STO, M+, or other such memory keys.

substitute To replace one part of a formula or equation with another quantity which is its equal.

switch A device that is used to open or close circuits, thereby stopping or allowing current flow in a circuit or through a component.

symmetrical Parts on opposite sides of a dividing line or median plane correspond in size, shape, and relative position.

tank circuit A parallel combination of an inductor and capacitor.

terminal A connection point on a device or component.

time constant The time it takes in seconds for a capacitor to charge up to approximately 63 percent of the applied voltage or the time it takes for a fully charged capacitor to discharge from 100 percent down to approximately 37 percent of full charge. Equal to the product of R (in ohms) times C (in farads) in a resistive-capacitive circuit. Also a measure of the current rise and fall in inductive circuits. Equal to the quotient of L/R in resistive-inductive circuits, L in henries, R in ohms. Symbol is Ω.

total current The total current supplied by a voltage source applied to a circuit.

transposing (rearranging) Moving a quantity from one side of an equation across the equal sign to the other side of the equation and changing its sign.

triggering The act of starting a horizontal sweep on an oscilloscope.

trigonometry The study of triangles and their relationships and functions.

troubleshooting A technique used to locate a problem in a circuit.

upper cutoff frequency The end frequency point defining the upper end of the bandwidth. For resonant circuits, the frequency above the resonant frequency at which the effect of resonance is considered to be outside of specified limits.

vector A line whose length represents a magnitude and whose direction represents its phase with respect to some reference.

vector addition The sum of two or more vectors.

vertical deflection The direction the trace on a scope will travel up and down periodically from a center reference point.

volt The unit of voltage or potential difference. Abbreviated V.

voltage A measure of the push or potential difference which makes each electron move. Symbol E. Unit is the volt.

voltage divider A type of circuitry that provides an economical way to obtain one or several lower voltages from a single higher voltage supply.

voltage drop Change in voltage available between points in a circuit produced by current flow through circuit components that provide opposition to current flow. Also called an IR, IX, or IZ drop. Unit is the volt.

voltmeter An instrument used to measure voltage between two points in a circuit.

watt The unit of power. Abbreviated W. Equal to one joule per second.

waveform amplitude The height of a measured electrical signal (e.g., sine wave) of voltage, current, or impedance on a scale representing the magnitude of the signal, the signal value.

waveform cycle A waveform that begins at any electrical degree point and progresses through a 360-degree change.

waveform frequency The number of waveform cycles occurring within one second of time.

waveform period (also referred to as waveform time) The time required to complete one cycle of the waveform.

working voltage The recommended maximum voltage at which a capacitor should be operated.