SPM Electrical & Electronics Engineering Studies key terms

The energy transferred per unit charge as charge moves between two points in a circuit, measured in volts. It drives current through a component and is measured across it, not through it.

The energy supplied per unit charge by a source such as a cell or generator, measured in volts. It is the open-circuit driving voltage before internal resistance reduces the terminal voltage.

The opposition a component offers to current flow, measured in ohms. For a fixed resistor it equals voltage divided by current; it converts electrical energy into heat and depends on material, length and cross-sectional area.

The relationship stating that current through a conductor is directly proportional to the potential difference across it, provided temperature stays constant. It applies to ohmic conductors but not to non-linear devices such as diodes or filament lamps.

The principle that the total current entering a junction equals the total current leaving it, because charge is conserved. It underpins nodal analysis of networks and explains current splitting in parallel branches.

The principle that the algebraic sum of potential differences around any closed loop in a circuit is zero, because energy is conserved. It is used with current law to solve multi-loop networks.

The resistance inside a source of EMF that causes its terminal voltage to fall as current is drawn. It dissipates energy as heat and limits the maximum current a cell can deliver.

Two ways of connecting components. In series, the same current flows through each and voltages add; in parallel, the same voltage appears across each and currents add. Each arrangement gives different total resistance.

A circuit of two or more resistors in series across a supply, used to obtain a fraction of the supply voltage. The output voltage is proportional to the resistance across which it is taken.

The ability of a device to store charge per unit of potential difference, measured in farads. A capacitor stores energy in an electric field and blocks steady direct current while passing changing signals.

A component of two conductors separated by an insulator that stores charge and energy in an electric field. It resists changes in voltage and is used for filtering, timing and coupling signals.

For an RC circuit, the product of resistance and capacitance, giving the time for a capacitor to charge to about 63 percent of its final voltage or discharge to about 37 percent. It sets the speed of timing and filter circuits.

The property of a coil that opposes changes in current by inducing an EMF, measured in henries. Energy is stored in a magnetic field, and the effect depends on rate of change of current.

The total opposition to alternating current from resistance plus reactance, measured in ohms. It combines magnitude and phase and determines current for a given AC voltage.

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

A two-terminal semiconductor device that conducts readily in one direction and blocks current in the reverse direction. It is used for rectification, protection and signal detection.

A diode designed to operate in reverse breakdown at a defined voltage, holding that voltage nearly constant. It is used for voltage regulation and overvoltage protection.

A three-terminal semiconductor device that can amplify signals or act as an electronic switch. In a bipolar transistor a small base current controls a larger collector current; field-effect types are controlled by gate voltage.

A material whose conductivity lies between that of conductors and insulators and can be controlled by doping, temperature or applied voltage. Silicon and germanium are common examples used to make diodes and transistors.

The conversion of alternating current into direct current using diodes. Half-wave rectification uses one diode and a smoothing capacitor; full-wave bridge rectifiers use four diodes for more efficient conversion.

A circuit that passes signals in some frequency ranges while attenuating others. RC and LC networks form low-pass, high-pass and band-pass filters used to remove noise or separate channels.

A circuit that increases the amplitude of a signal using an external power supply. Voltage gain is output voltage divided by input voltage, and bandwidth limits the useful frequency range.

A high-gain integrated amplifier with inverting and non-inverting inputs, usually used with negative feedback. It forms comparators, summing amplifiers and active filters, and its ideal model has infinite gain and input impedance.

A digital circuit that produces an output determined by Boolean combinations of its inputs, such as AND, OR, NOT and NAND. Gates are the building blocks of combinational and sequential digital systems.

A mathematical system of binary variables and operations used to describe and simplify digital logic. Rules such as De Morgan's theorems allow a logic circuit to be reduced to fewer gates.

A table listing every possible combination of inputs to a logic circuit alongside the corresponding output. It defines combinational behaviour and allows a Boolean expression or gate network to be derived.

Returning a fraction of a system's output to its input. Negative feedback reduces gain but improves stability, bandwidth and linearity; positive feedback can cause oscillation or latching.

A device that converts a physical quantity such as temperature, light or strain into an electrical signal. Its output may be analogue or digital and is often conditioned before use in a control system.

A device that converts one form of energy into another, for example sound to electrical energy in a microphone. Sensors and actuators are transducers used at the input and output of control systems.

An arrangement of components that regulates a process to keep an output near a desired value. Open-loop systems act without checking output; closed-loop systems use feedback to reduce error.

The generation of an EMF in a conductor when it experiences a changing magnetic flux, as described by Faraday's law. It is the basis of generators, transformers and induction motors.

A device of two coils on a shared magnetic core that changes alternating voltage by mutual induction. The voltage ratio equals the turns ratio, and power is transferred with only small losses.

An AC supply of three voltages equal in magnitude and separated by 120 degrees in phase. It gives constant power delivery, smaller conductors and is standard for industrial motors and distribution.

The conductors and associated equipment that carry electrical power at high voltage from generation to distribution networks. High voltage reduces current and therefore resistive losses for a given power.

The cosine of the phase angle between voltage and current in an AC circuit, equal to real power divided by apparent power. A low value means more current for the same useful power and higher losses.

The conversion of electrical energy into heat in a component, calculated as current squared times resistance or voltage times current. It determines ratings, heating and efficiency losses in circuits and cables.

Connecting exposed metalwork and circuit points to earth so fault current flows and protective devices disconnect quickly. Bonding links metal parts to keep them at the same potential and prevent shock.

A protective device that trips when the current in live and neutral conductors differs, indicating leakage to earth. It protects people from electric shock at currents well below those needed to blow a fuse.

Overcurrent protective devices that interrupt a circuit when current exceeds a safe value. A fuse melts a wire element and must be replaced; a circuit breaker trips a mechanism and can be reset.