RBSE SS Voc Electrical and Elect key terms

The electrical pressure between two points that pushes charge around a circuit, measured in volts. It is the energy transferred per unit charge between those points.

The energy per unit charge supplied by a source such as a battery or generator to drive current around a closed circuit. It is measured in volts even though it is not a force.

The assumed direction of flow from the positive terminal through an external circuit to the negative terminal, opposite to actual electron movement in metal conductors. Circuit arrows and formulas conventionally follow this direction.

The relationship stating that current through a conductor is directly proportional to voltage across it and inversely proportional to resistance, written V = I × R for constant temperature.

The opposition a material offers to current flow, converting electrical energy into heat. It is measured in ohms and depends on material, length, cross-sectional area and temperature.

An intrinsic property of a material describing how strongly it resists current, expressed in ohm-metres. It allows resistance of a conductor to be calculated from its length and cross-sectional area.

The relationship for electrical power in watts, given by P = V × I, with variants P = I²R and P = V²/R for resistive loads. It is used to size cables, fuses and supplies.

A circuit where components are connected end to end so the same current flows through each. Total resistance is the sum of the individual resistances and voltage divides between them.

A circuit where components are connected across the same two nodes, so each has the same voltage but currents divide. Total resistance is always lower than the smallest branch resistance.

Two or more resistors in series across a supply, producing a fraction of the supply voltage across one of them. It is widely used for biasing and sensing in electronic circuits.

Two rules for circuit analysis: current entering a node equals current leaving it, and the algebraic sum of voltages around any closed loop is zero. They apply to any network, linear or not.

The ratio of true power in watts to apparent power in volt-amperes in an AC circuit, equal to the cosine of the phase angle between voltage and current. A low value increases supply current.

Deliberate connection of exposed metalwork and the supply neutral point to earth so fault current trips protection and touch voltage stays safe. It is the foundation of shock prevention in installations.

A supply arrangement in which the neutral conductor is earthed at several points along the distribution network and also serves as the protective conductor for consumers' installations.

A protective device that continuously compares current in live and neutral conductors and trips when a small imbalance indicates leakage to earth, typically 30 mA for personnel protection.

A resettable overcurrent device with a thermal element for overloads and a magnetic element for short circuits. It is rated by current and breaking capacity and replaces fuses in modern boards.

A deliberate weak link containing a metal element that melts when current exceeds its rating, opening the circuit. It protects against overload and short circuit but must be replaced after operation.

The maximum fault current a protective device can safely interrupt without damage or dangerous arcing. It must exceed the prospective short-circuit current at the point of installation.

A static device with two or more windings on a common magnetic core that changes AC voltage level by mutual induction, with power roughly conserved and frequency unchanged.

The number of primary turns divided by the number of secondary turns of a transformer. It fixes the ratio of primary to secondary voltage and the inverse ratio of currents.

Circulating currents induced in the magnetic core of a machine or transformer by changing flux, causing heating and energy loss. They are reduced by laminating or powdering the core.

Energy dissipated as heat each time the magnetic domains of a core are reversed by alternating flux. It depends on the core material and frequency and is reduced by using silicon steel.

The speed of the rotating magnetic field in an AC machine, equal to 120 times frequency divided by number of poles. An induction motor always runs slightly below this value.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a percentage of synchronous speed. Slip must exist for torque to be produced.

A system of three alternating voltages of equal magnitude and frequency, displaced by 120 electrical degrees. It gives constant power delivery and rotating fields for motors.

A three-phase connection where one end of each of the three windings joins at a common neutral point. Line voltage is √3 times phase voltage and line current equals phase current.

A two-terminal semiconductor device that conducts readily in one direction and blocks the other. It is used for rectification, protection and clamping in electronic circuits.

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

A circuit that converts alternating current into unidirectional current, using one diode for half-wave or four for full-wave bridge operation, usually followed by smoothing.

The ratio of the alternating component of a rectifier output to its average direct component, indicating how much smoothing remains to be done. Lower values mean a cleaner DC supply.

A three-terminal semiconductor device in which a small base or gate signal controls a much larger collector or drain current. It serves as an amplifier or an electronic switch.

Setting the steady direct voltages and currents at a transistor's terminals so it operates in the intended region, such as active, cut-off or saturation, before any signal is applied.

A circuit that increases the amplitude of a signal while drawing energy from a separate supply. Its performance is described by gain, bandwidth, input impedance and distortion.

A circuit that generates a continuous repetitive waveform without an external signal input, using positive feedback and a frequency-selective network to set the output frequency.

A basic digital circuit that produces one output state from one or more binary inputs according to a fixed rule, such as AND, OR, NOT, NAND or NOR.

A table listing every possible combination of inputs to a logic circuit alongside the resulting output for each combination. It fully defines combinational logic behaviour.

A set of rules for manipulating binary variables using operations AND, OR and NOT, used to simplify logic expressions before implementing them with gates.

A test instrument that plots signal voltage against time on a screen, allowing amplitude, period, frequency and phase to be measured. Modern versions are usually digital storage types.

A combined instrument for measuring voltage, current and resistance, with additional ranges such as continuity and diode test. A clamp attachment allows current measurement without breaking the circuit.

A four-arm resistive network used to measure an unknown resistance by balancing two potential dividers. At balance the galvanometer reads zero and the unknown is found from the ratio arms.

A check using a meter's low-resistance range to confirm an intended conductive path exists, often with an audible tone. It is done on a de-energised circuit for safety.

Joining metal parts with a filler alloy melted at a temperature below the workpieces' melting points. In electronics, flux-cored tin-lead or lead-free solder forms a reliable electrical and mechanical bond.

A soldered connection that looks dull, grainy or blobby because the joint was disturbed or too cool while solidifying. It has high resistance and is a common intermittent fault.

A chemical agent applied during soldering to remove oxide from the surfaces and help the filler alloy wet and flow. Residue from some fluxes must be cleaned to prevent corrosion.

An insulating board with copper tracks etched in a designed pattern to connect components, replacing point-to-point wiring. It provides repeatable, compact and mechanically stable assemblies.

Scheduled inspection, cleaning, tightening, lubrication and testing carried out before faults occur, to keep equipment reliable and safe. Records of these activities support planning and warranty claims.

A safety procedure in which the energy source of equipment is isolated, locked and tagged so it cannot be re-energised while work is in progress. Only the person who applied the lock removes it.

A structured look at a task to identify hazards, judge how likely and severe any harm is, and record control measures before work starts. It is a legal duty in most workplaces.

Items worn or used by a worker, such as insulated gloves, safety footwear, goggles and arc-rated clothing, to reduce exposure to hazards that cannot be eliminated otherwise.

Working out the total expense of a job by adding material, labour, overheads and contingency, then setting a price that covers costs and leaves a margin. It underpins quotes and profitability.

A reasoned prediction of the time, materials and cost a job will require, based on measurements and past experience. It becomes a quotation once price and terms are fixed.

The level of sales or work volume at which total revenue equals total costs, so neither profit nor loss is made. Anything above it contributes to profit.