ETA CETa key terms

The electrical pressure that pushes charge between two points. Measured in volts (V). One volt equals one joule of energy delivered per coulomb of charge moved between those points.

The rate at which electric charge flows past a point in a circuit. Measured in amperes (A); one ampere means one coulomb of charge passing each second.

The opposition a material offers to current flow, converting electrical energy into heat. Measured in ohms (Ω). Depends on material, length, cross-sectional area, and temperature.

The relationship stating that voltage equals current multiplied by resistance (V = I × R). In a purely resistive circuit, current rises proportionally as voltage rises.

The rate at which electrical energy is transferred or dissipated. Measured in watts (W); computed as voltage times current (P = V × I) or as current squared times resistance.

The total amount of work electricity performs over time, equal to power multiplied by duration. Billed and stored in watt-hours or kilowatt-hours rather than in watts.

Current that flows in one fixed direction with a steady polarity. Supplied by batteries, solar cells, and regulated power supplies, and used inside most electronic circuits.

Current that reverses direction periodically, usually following a sine wave. Described by its frequency in hertz and by its peak or RMS amplitude; used for mains distribution.

The number of complete cycles a repeating waveform completes each second, measured in hertz (Hz). One hertz equals one cycle per second; period is its reciprocal.

The time taken for one complete cycle of a repeating waveform, measured in seconds. It is the reciprocal of frequency, so a 50 Hz wave has a period of 20 ms.

The physical distance between corresponding points on successive cycles of a wave, such as crest to crest. Equals wave speed divided by frequency; shorter at higher frequencies.

The position of a point in a repeating waveform's cycle, expressed as an angle in degrees or radians. Phase difference describes how far one signal leads or lags another.

The effective value of an alternating waveform, equal to the DC voltage or current that would deliver the same heating power. For a sine wave it is peak divided by about 1.414.

The maximum instantaneous magnitude reached by a waveform during a cycle, measured from zero. A sine wave's peak is about 1.414 times its RMS value.

The total swing of a waveform from its most negative point to its most positive point. For a symmetrical sine wave it equals twice the peak value.

A two-terminal component built to provide a specific resistance, limiting current and setting voltage levels. Marked by colour bands or printed codes; rated also for maximum power dissipation.

A standard scheme in which coloured bands on a resistor encode its value and tolerance. Each colour maps to a digit, and a final band shows how far the true value may vary.

The permitted deviation of a component's actual value from its marked value, usually given as a percentage. A ±5% resistor may differ from its nominal value by five percent either way.

A component that stores electric charge in an electric field between two conducting plates separated by a dielectric. Blocks steady DC while passing changing signals; measured in farads.

The ability of a device to store charge per unit of applied voltage, measured in farads (F). One farad holds one coulomb at one volt; practical parts use micro and nano prefixes.

An insulating material placed between capacitor plates that increases capacitance and withstands voltage stress. Its relative permittivity, or dielectric constant, sets how much the capacitance rises.

A coil that stores energy in a magnetic field created by current through it. Opposes changes in current, passes steady DC easily, and is measured in henries (H).

The property of a circuit that opposes a change in current by inducing a voltage, measured in henries (H). Depends on coil turns, core material, and geometry.

The total opposition to alternating current flow, combining resistance with reactance and measured in ohms. It is a complex quantity with both magnitude and phase angle.

The frequency-dependent opposition to alternating current from a capacitor or inductor, measured in ohms. Capacitive reactance falls as frequency rises; inductive reactance rises with frequency.

A circuit in which components form a single path so the same current flows through each. Total resistance is the sum of the individual resistances; the supply voltage divides among them.

A circuit in which components connect across the same two nodes, so each has the same voltage. Total resistance is less than the smallest branch, and branch currents add together.

The rule that the algebraic sum of voltages around any closed loop in a circuit equals zero. It follows from energy conservation and supports loop analysis of networks.

The rule that the total current entering a node equals the total current leaving it. It follows from charge conservation and underpins nodal analysis of circuits.

A two-terminal semiconductor device that conducts readily in one direction and blocks the other. Used for rectification, protection, and clamping; a silicon diode drops about 0.7 V when conducting.

The condition where voltage is applied across a diode in its conducting direction, lowering the barrier and allowing current. Silicon needs roughly 0.7 V; germanium about 0.3 V.

The condition where voltage is applied across a diode in its blocking direction, widening the depletion region. Only a tiny leakage current flows until breakdown voltage is reached.

A diode designed to operate safely in reverse breakdown, holding a nearly constant voltage. Used to regulate or clamp voltage; its Zener voltage is set by doping during manufacture.

A circuit that converts alternating current into pulsating direct current using diodes. Half-wave types use one diode; full-wave bridge types use four and exploit both half-cycles.

The small residual alternating variation left on a DC supply voltage after rectification. Reduced by smoothing capacitors and filters; specified as a peak-to-peak or RMS percentage.

A three-terminal semiconductor device that amplifies or switches signals. In a bipolar transistor a small base current controls a larger collector current; field-effect types control current with gate voltage.

The steady DC voltage or current deliberately applied to a device to set its operating point. Correct bias keeps a transistor in the desired region for linear amplification or reliable switching.

The DC operating point of an amplifying device when no signal is applied, often called the Q-point. Set by bias so the signal swings without clipping in the linear region.

The ratio of a circuit's output amplitude to its input amplitude, often expressed in decibels. Voltage gain and power gain differ; a gain below one means the stage attenuates.

A logarithmic unit for expressing ratios of power or amplitude. Power ratio in dB is ten times the base-ten logarithm; amplitude ratio uses twenty times the logarithm.

The reduction in signal strength as it travels through a medium or network, usually stated in decibels. Caused by resistance, cable loss, and intentional resistive pads.

A network that passes some frequencies while blocking others, shaping a signal's spectrum. Classified as low-pass, high-pass, band-pass, or band-stop, and built from resistors, capacitors, and inductors.

A circuit that increases the amplitude of a signal using energy from a power supply. Described by its gain, bandwidth, input impedance, output impedance, and distortion.

The time for a capacitor-resistor circuit's voltage or current to change by about 63% of its final step. Equals resistance times capacitance; five time constants approximate full charge.

A device converting stored chemical energy into electrical energy, with a fixed nominal voltage set by its chemistry. Characterised by capacity in ampere-hours and internal resistance.

A material whose electrons are tightly bound, so it offers very high resistance to current. Examples include glass, rubber, and dry air; used to isolate conductors.

A material with loosely bound electrons that permits current to flow easily, such as copper or aluminium. Its resistance rises with length and falls with greater cross-sectional area.

A test instrument that plots voltage against time on a screen, showing waveform shape, amplitude, and timing. Controls set vertical scale in volts per division and timebase in seconds per division.

A general-purpose test instrument measuring voltage, current, and resistance, often with continuity and diode tests. Correct function and range selection is essential to avoid damage or unsafe readings.

A pair of magnetically coupled coils that changes AC voltage levels without direct electrical connection. The turns ratio sets the voltage ratio; it does not work on steady direct current.