Electrical Terms




Alternating Current (ac)     Current from a power source that changes polarity periodically.

Alternator     A device that supplies alternating current.

American wire gauge (AWG)    A standard for wire sizes, with the smallest being designated as forty (40) and the largest as four aught (4/0).

Ammeter     An instrument used for measuring current.

Ampacity    The current–carrying capacity of conductors in amperes.

Ampere (A)    The unit of measurement for current. One ampere is that current whereby one coulomb of charge passes through a point in one second. Named for André Ampere.

Ampere-hour (Ah)   Unit of measurement for cell or battery capacity.  One Ah generally  means that a current of one amp has been flowing for one hour.

Amplifier   An electronic circuit that boost the voltage and/or the current level of a signal.

Analog     Generally refers to signals that have many discrete values versus digital binary signal that have only two states.

Apparent power     The product of voltage times current in a circuit containing reactive loads and measured in volt-amps.

Armature     The moving part of a motor or generator.

Autotransformer     A power transformer having one continuous winding that is tapped.




Ballast     A device used to provide starting current for certain types of lamps (fluorescent).

Battery     A direct-current power source consisting of two or more cells.

Binary  In electronics, a number system that has two as its base; therefore any position has only two possible values, 0 or 1.  A signal that has only two possible states at any instance.

Bit      A single binary digit, can be either a 0 or 1.

Brush      A conductive block used to make sliding contact with an armature.

Byte    A group of eight binary bits, commonly used to represent digital data.




Cable     A stranded conductor or group of individual conductors insulated from each other.

Capacitance (C)     The ability of two conductors separated by an insulator to store an electrical charge; measured in farads (F).

Capacitive reactance (XC)      The opposition that a capacitor offers to alternating current.  This opposition, in the form of a counter electromotive force (cemf), expressed in ohms.

Capacitor       A device designed to provide a specific amount of capacitance.

Cell        A device that transforms one form of energy into electrical energy.  An example would be a chemical dry cell commonly used in flashlights (D, C, AA, AAA) and other electric devices.  These are often referred to as batteries (though technically a battery contains 2 or more cells).

Circuit       An arrangement or connection of circuit devices and components to perform a specific objective.  In the simplest form it would require an energy source, a load to transform the energy into the desired task, and conductors to connect the source to the load.  In most applications a control device (switch) would be included and may also include a protective device.  Common example of a simple circuit would be a flashlight.

Circuit breaker      A circuit protection device that opens the circuit automatically when an overload or short circuit occurs.

Closed circuit        A circuit that provides a complete path for current.

Coil      A wound spiral of two or more turns of insulated wire, used to introduce inductance into a circuit, produce a magnetic field from current flow, or to respond to a changing magnetic field by producing a voltage or mechanical motion.

Commutator       A cylindrical arrangement of insulated metal bars connected to the armature coils of a direct-current electric motor or generator, providing a unidirectional current from the generator or a reversal of current into the coils of the motor.

Conductance (G)    The ability of a conductor to allow the flow of electrons. Measured in Siemens (S).  The reciprocal of resistance.

Conductor      A low-resistance material to provide a path for current.  Used to interconnect components in a circuit.

Conventional current     A direction flow assignment that has current flowing from positive to negative.

Coulomb      Base unit of electrical charge equal to 6.25 X 1018  electrons. Named for Charles Coulomb, the French physicist who pioneered research into magnetism and electricity. He also formulated Coulomb’s law which states that the force of attraction or repulsion between two charged bodies is equal to the product of the two charges and is inversely proportional to the square of the distance between them.   F= Q1 x Q2/d2

Crystal       A natural or synthetic crystalline material having piezoelectric properties. As a transducer, used to convert dynamic pressures (vibrations) to ac electricity or change ac electricity into vibrations.

Current (I)     The rate of flow of electrons through a conductor or component; measured in amperes.  The symbol (I) stands for intensity of the electron flow.

Cycle    One complete wave of alternating voltage or current.




Dielectric     A nonconductor of electricity. An insulator that is capable of concentrating electric fields.

Difference of potential      See electromotive force and voltage.

Digital     Generally in electronics, refers to signals, devices, or circuits that are binary, meaning they only have two states (high or low, 1 or 0, on or off).

Diode     A semiconductor device that only allows current to pass through it in one direction, cathode to anode.  Also, a classification of semiconductor devices having only one junction.  Examples include: rectifier, zener, varactor, and tunnel diodes.

Direct Current (dc)    Current from a power source that continually flows in the same direction.   An electrical source of constant polarity.

Duty Cycle     The ratio of pulse width to period, indicates the percentage of time a pulse is present during a cycle.




Electricity   The physical phenomena arising from the behavior of electrons and protons that is caused by the attraction of particles with opposite charges and the repulsion of particles with the same charge.  The physical science of such phenomena.  Also, electric current used or regarded as a source of power.

Electric energy      The energy carried by free electrons from a source to a load. Also, the potential energy of a stationary charge.

Electric power (P)    The rate at which energy is consumed in a circuit or load.  Measured in watts (W).

Electrolyte      A chemical solution used in cells and some capacitors to produce an electrically conductive medium.

Electrolytic capacitor     A capacitor whose dielectric is formed through the reaction of an electrolyte and its electrodes.

Electromagnet    A device that produces a magnetic field as the result of current flow through a coil of wire.

Electromechanical      A classification of actions or devices whereby a mechanical action is caused by the forces of attraction or repulsion created when current flow generates magnetic fields (electromagnetic).

Electromotive Force (emf)     The force or electrical pressure that has the potential to cause electron flow in a circuit.  Also called voltagepotential difference or difference of potential.  Measured in volts (V).

Electrostatic field     An electric field produced by stationary charges.




Farad (F)     The basic unit of measurement for capacitance.  One farad is that capacitance that will store one coulomb of charge when the charging force is one volt.  Since the farad is a very large unit, capacitance will more commonly be expressed as microfarad (uF) or picofarad (pF) values. Named for Michael Farady,  the British physicist and chemist who discovered electromagnetic induction and proposed the field theory later developed by Maxwell and Einstein.

Filter    A circuit designed to pass a specific frequency range while rejecting all others.

Flux    Generally refers to a magnetic line of force but may also describe an electric line of force.

Frequency        The number of cycles per second for a periodic waveform.  Measured in hertz (Hz).

Fuse     A protective device designed to interrupt current flow (open) through a circuit when current exceeds a rated value.




Gauss       A unit of measurement for magnetic field.

Generator      A device that converts mechanical energy to electrical energy.

Ground     Serves as a reference point for measuring all other potentials in a circuit.  Generally assumed to be at zero potential with respect to the earth.  Other than earth references may be used such as the chassis of an automobile (chassis ground) or some arbitrary point in a circuit (circuit ground) like the negative side of the power source.

Grounded Conductor    A circuit conductor that is intentionally connected to earth ground, often a neutral.




Heat sink    A device attached to a component to aid in the dissipation of heat.

Henry (H)    The unit of inductance in which an induced electromotive force of one volt is produced when the current is varied at the rate of one ampere per second.  Named for Joseph Henry, an American physicist who performed extensive studies of electromagnetic phenomena.

Hertz (Hz)    A unit of frequency equal to one cycle per second. Named for Heinrich Hertz,  a German physicist who was the first to produce radio waves artificially.




Impedance (Z)     Opposition to current flow from the combined effects of resistance and reactance measured in ohms (S).

Inductance (L)     The property of a circuit that opposes a change in current. Also, the property of a circuit to store energy in the form of a magnetic field and release it back into the circuit at a later time.

Inductive Reactance (XL)    The opposition that an inductor offers to alternating current.  This opposition, in the form of a counter electromotive force (cemf), is expressed in ohms.

Inductor     An electrical device designed to provide a specific amount of inductance; measured in henrys (H).

Insulation     Nonconductive material used to cover wires and components to prevent shock and short circuits.

Insulator    A material that has a high resistance to current flow.

Integrated Circuit (IC)    The placement of numerous components and circuits on to a silicon chip.

Internal resistance      The resistance within a power source.

Inverter    A device that converts dc to ac.  Also refers to a logic device (NOT function) whose output is always opposite the input.




Joule     The basic unit of electrical, mechanical, and thermal energy. As a unit of electrical energy it is equal to the energy carried by 1 coulomb of charge being propelled by an electromotive force of 1 volt.  Named for James Joule, the British physicist who established the mechanical theory of heat and discovered the first law of thermodynamics.




Kilo (k)      Metric prefix for units of measurement equal to thousands (1000 or 103). As an example: 1 kilohertz (kHz) equals 1000hz.

Kilowatthour  (kWh)     Unit of energy consumption equal to 1000 watt-hours or the energy consumed at the rate to one kilowatt (kW) for a time of one hour.  Equivalent to 3,600,000 joules.  Generally used to specify a large energy consumption over a specific time interval.  Residential energy is usually priced at the number of kilowatt-hours used for a month.

Kirchhoff,  Gustav Robert       The German physicist noted for his research in spectrum analysis, optics, and electricity.  Developed fundamental DC circuit laws dealing with current characteristics in a parallel circuit and voltage characteristics in a series circuit. His current law states that the current entering a connection has to equal the current leaving that connection, and that the sum of the load currents has to equal the source current (or sum of source currents for multiple parallel sources) (I= I1+I2+——+IN).  His voltage law states that around any closed loop of series connected components, the sum of the voltage drops must equal the source voltage (or sum of source voltages for multiple series connected sources. (V= V1+V2+ —— +VN).




Lamp       A light producing device consisting of a filament placed in a vacuum.

Law of magnetic poles      Like poles repel, unlike poles attract.

Lenz’s Law    Basic law of electromagnetic induction which states that an induced voltage will have a polarity that opposes the current change that produced it.

Light-emitting diode (LED)     A semiconductor diode that emits light as current flows from the cathode to the anode across its PN junction.

Linear     A circuit or component where the output is a straight line (direct proportion) function of the input.

Load      A device or apparatus that uses the energy of a circuit to perform work.  May also refer to the power used by a device, machine, or a combination of many.




Magnet     An object which produces a magnetic field in the surrounding space.

Magnetic field     The detectable magnetic flux issuing from a magnet or electromagnet.

Magnetic poles     The two points of strongest concentration of magnetic flux around a magnet or electromagnet.  By assignment the flux leaves the north pole and returns to the south pole.

Magnetic saturation      The point where an increase in magnetic force  produces no further magnetic effect in a magnetic material.  The material can have no further increase in flux. Iron, nickel, cobalt, and their alloys are considered to be magnetic materials.

Magnetism    The physical phenomena exhibited by magnets and electric current flow that is represented by lines of force.

Microprocessor    A CPU that is manufactured on a single integrated-circuit  (IC) chip.

Modem     Abbreviation for modulator-demodulator.  A device that converts data from one form into another, as from one form usable in data processing to another form usable in telephonic transmission.

Multimeter     An instrument that can measure current, voltage, and resistance on various ranges.  Many multimeters can measure other circuit values such as frequency and capacitance.  May have digital (DMM) or analog displays (VOM).




Negative   For sources, implies the terminal that has an excess of electrons.  Also, can imply the polarity of a point in a circuit in respect to some other point.

Nonlinear    A circuit or component whose output versus input graph is not a straight line.

Norton’s theorem     A method of reducing a complex network of bilateral (conducts equally well in both directions) components to one current source and one shunt resistance across the load terminals.




Ohm (Ω)     The unit of measurement for resistance. Named for Georg Simon Ohm, the  German physicist noted for his contributions to mathematics, acoustics, and the measurement of electrical resistance.  One ohm is that resistance that limits the current to one ampere when a potential of one volt exist across its terminals.

Ohm’s law     Very basic circuit law that defines the relationships between current, voltage, and resistance in a DC circuit.  Ohm’s law states that current is directly proportional to voltage and inversely proportional to resistance. (I = V/R)  The other forms  of the formula are  V = IR and R = V/I.

Ohmmeter     An instrument for measuring resistance.

Operational Amplifier (Op Amp)     A highly stable direct coupled amplifier resistant to oscillation.  May be packaged in an IC format.

Oscillator    A circuit that converts dc power into ac signals with constant frequency.  Also, an instrument that generates  ac signals whose frequency and amplitude can be varied.  These are also referred to as signal generators.

Oscilloscope     An instrument that displays a plot of voltage over time.  Often referred to as a scope.

Overload     A load in excess of the design limit for a circuit.




Parallel circuit     A circuit with two or more loads (or sources) connected such that all have the same voltage but different currents.  Each load can be operated independent of the others.  Parallel sources should have equal voltage ratings.

Period     The time in seconds that is required to complete one cycle of a waveform.

Permeability      The ability of a magnetic material to conduct magnetic lines of force.

Phase      A time relationship between two electrical quantities.

Polarity      For electrical charge, the indication of a charge as either positive (+) or negative (-).  Voltage at a point would be indicated as being either positive or negative with respect to some other point.  For magnetic poles, the indication as either north or south.

Positive    For sources, implies the terminal that has a deficiency of free electrons.  Also, can imply the polarity of a point in a circuit in respect to some other point.

Potentiometer    A three-terminal resistor with an adjustable center connection generally used to control voltage; widely used for volume control in radio and television receivers. In this sense, also called a Pot.

Power   The rate at which energy is consumed.  In electronics it refers to the consumption of electrical energy in joules over time; measured in watts.

Power factor(PF)   The ratio of true power to the apparent power in a circuit, especially those that are not purely resistive.   It is also equal to the cosine of the phase angle for the circuit.

Power supply     Generally, a device or circuit used to convert alternating current (ac) of specific voltage to one or more direct current (dc) values of specific voltage and current ratings. May have variable voltage ability in some instances.  May also refer to a device that converts a specific dc value to another dc value (dc to dc converter).

Primary cell      A device that uses up its ingredients to convert chemical energy to electrical energy and therefore can not be recharged.

Primary winding      The input winding to a transformer.

Printed circuit (PC) board     A fiberglass board with copper foil as the conductors to interconnect the attached electrical components.




Random-access memory (RAM)   A read/write memory that allows date storage (Write) and data retrieval (Read) to any location in any order.   Considered to be temporary (volatile) in that the contents are lost if power is turned off.

Reactance    Opposition to current offered by capacitors and inductors in the form of a counter-electromotive force (cemf), but expressed in ohms.  Reactance does not consume power but gives the appearance that it does.

Read only memory (ROM)   A classification of non-volatile memory that has its contents built in at time of manufacturer and which cannot be changed and cannot be lost if power is turned off.   Variations include Programmable (PROM) and Erasable Programmable (EPROM) which has provisions for user programming.

Rectifier     A solid state device that converts alternating current to pulsed direct current.

Relay     An electromechanical device that uses electromagnetism to mechanically switch electrical circuits.  The output contacts are designed to be either normally open (NO) or normally closed (NC).  Some relays provide both arrangements and multiple switches.

Resistance (R)   The opposition to current flow in a circuit; measured in ohms.

Resistor     An electrical component designed to provide a specific resistance.  Available in many formats such as fixed, tapped, and variable.  See potentiometer and rheostat.

Resonance     A circuit condition when the inductive reactance (XL) equals the capacitive reactance (XC).  A resonant circuit is one that has been tuned to that condition and resonant frequency is that frequency that resonance occurs in a circuit and provides a maximum output for one of its circuit variables.

Rheostat      A two-terminal resistor with an adjustable center connection and one end connection generally used to control current.

Ripple      The small amount of ac voltage that still remains in the output of a dc power supply.

RMS   Root mean square    The value of an ac sine wave that indicates its equivalent dc value for producing heat.  Also called the effective value, it is equal to 70.7% of the maximum value (peak value) for a pure sine wave.




Schematic or schematic diagram      A drawing dipicting how the components are connected using standarized symbols.

Secondary cell     A device whose ingredients convert chemical energy to electrical energy but can be recharged.

Secondary winding      The output winding of a transformer or one of several output windings.

Series circuit      A circuit arrangement of two or more loads (or sources) connected end-to-end only allowing for one current path.  Therefore, all components have the same current but can have different voltage.  An open at any point or in any component interrupts current flow for all.

Semiconductor     Any of various solid crystalline substances, such as germanium or silicon, having electrical conductivity greater than insulators but less than good conductors.   In electronics these are generally doped to from either N type or P type material.  These materials are the foundational material for diodes and transistors.

Short circuit      An undesirable low resistance path between two points in a circuit.

Siemen (S)          The unit of measurement for conductance. Named for Ernst Werner von Siemens, a German engineer who made notable improvements to telegraphic and electrical apparatus.

Silicon-controlled rectifier (SCR)   See thyristor

Sine wave    A waveform whose instantanous amplitude is a function of the sine of the angle of rotation for that instant.   The output waveform produced by rotating a loop in a magnetic field, and the output of an oscillator generating a pure frequency.

Solar cell     A device that converts light energy to electrical energy. Also called a photovoltaic cell.

Solder    Any of various fusible alloys, usually tin and lead, used to join metallic parts. In electronics used to connect components to PC boards or to aid the conductivity and mechanical junctions of connections and splices.

Solenoid     Electromechanical device that use electromagnetism to produce a mechanical operation.

Solid-state      The term that describes components or circuits that use semiconductors technology.

Source      General term to describe devices that provides electrical energy at their output terminals to operate a circuit.  Examples: battery, solar cell, generator and alternator, or power supply.

Static electricity    A stationary electrical charge on an object.

Stator      The electromagnetic part of a motor or generator that does not rotate.

Stepper motor    A motor type driven with digital codes that moves in discrete angular increments with each code change.

Superposition theorem    A method for analyzing a complex network of bilateral (conducts equally well in both directions) components having multiple sources.

Surge     A very rapid increase of current or voltage.

Switch     A device used to open (turn off) and close (turn on) electrical circuits that can  be designed to operated by numerous actions such as toggle, slide, and pushbutton actions. Standard configurations include SPST, SPDT, DPST, and DPDT.




Terminal     A connection point for electrical components or conductors.

Thermistor      A resistor made of semiconductor material having resistance that varies rapidly and predictably with temperature.  Used as a temperature sensor, the resistance varies inversely with temperature.

Thermocouple    A thermoelectric device used to measure temperatures accurately, consist of two dissimilar metals joined so that a potential difference is generated that is representative of the temperature of the junction.

Thevenin’s theorem     A method of reducing a complex network of bilateral (conducts equally well in both directions) components to one voltage source and one resistor in series with the load terminals.

Thyristor     A broad classification of semiconductor devices used as electronic switches.  Examples include diacs, SCRs, and triacs.

Tolerance     Used to describe the allowable variance in a measurement or a components value.

Transducer    A device used to convert input energy of one form into output energy of another.

Transformer      A device used to transfer electric energy from one circuit to another, especially a pair of multiply wound, inductively coupled wire coils that effect such a transfer with a change in voltage, current, phase, or other electric characteristic. Generally used to convert one voltage-current relationship to another. Step-up transformer, increase the voltage while decreasing the current, and step-down transformer decrease the voltage while increasing the current.

Transistor     A small electronic semiconductor device having at least three electrical contacts, used in a circuit as an amplifier or a switch. See: BJT, JFET, MOSFET.

True power     The actual power consumed by a circuit; measured in watts.







Volt (V)     The unit by which an electromotive force or voltage is measured. Named for Alessandro Volta, the Italian physicist who invented the first electric battery (1800).

Voltage (V)      Same as emf.  The force or electrical pressure that has the potential to cause electron flow in a circuit.

Voltage divider      A series circuit that divides voltage.

Voltage drop      The difference in potential between two points caused by current flow through a component.

Voltmeter     An instrument used to measure voltage.




Watt (W)     The unit of measurement for power.  One watt equals to the work done when one joule is used per second. Named for James Watt the British engineer and inventor.

Watt-hour (Wh)     Unit of energy consumed at the rate of one watt (W) for a time of one hour.  Equivalent to 3,600 joules.

Wiring diagram     A graphic representation of how circuit components are connected.




Zener Diode     A semiconductor device designed to operate at a fixed voltage as a voltage regulator.

Comments are closed.