WBBSE Madhyamik Power (Vocational) key terms

The rate at which electric charge flows past a point in a circuit, measured in amperes. One ampere equals one coulomb of charge passing each second.

The work done per unit charge in moving charge between two points in a circuit, measured in volts. It is the electrical 'push' that drives current through a conductor.

The opposition a material offers to the flow of electric current, measured in ohms. It converts electrical energy into heat and depends on material, length, and cross-sectional area.

A relationship stating that current through a conductor is directly proportional to the potential difference across it, provided temperature stays constant. It is written as V equals I times R.

A property of a material showing how strongly it resists current for a given length and cross-section, measured in ohm-metres. Copper has low resistivity; nichrome has high resistivity.

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

A circuit in which components are connected across the same two points so each receives the same voltage. Total resistance is less than the smallest branch resistance and current divides among branches.

Electromotive force, the energy per unit charge supplied by a source such as a cell or generator, measured in volts. It differs from terminal voltage because of internal resistance.

The resistance inside a source of EMF that causes its terminal voltage to fall when current is drawn. It wastes energy as heat within the cell or generator.

The rate at which electrical energy is transferred or converted, measured in watts. In a circuit it equals voltage multiplied by current, or current squared multiplied by resistance.

The total work done by an electric circuit over time, measured in joules or in kilowatt-hours for billing. It equals power multiplied by the time for which power flows.

A material that allows electric current to flow easily because it contains free electrons. Copper, aluminium, and silver are common conductors used in wiring and cables.

A material that resists the flow of electric current and is used to separate or cover conductors for safety. Rubber, PVC, porcelain, and dry wood are typical examples.

Connecting exposed metal parts of an installation to the earth through a low-resistance path so fault current flows safely to ground and protective devices operate.

A protective device containing a thin wire that melts and breaks the circuit when current exceeds a safe value, preventing damage from overload or short circuit.

A miniature circuit breaker that automatically trips to open a circuit on overload or short circuit and can be reset by hand, unlike a fuse which must be replaced.

A condition in which a circuit carries more current than its design permits for a long period, causing overheating. Protective devices such as fuses and MCBs respond to it.

An accidental low-resistance path between two points at different potentials, causing a very large current to flow. It can damage equipment and start fires unless protection acts quickly.

One or more insulated conductors enclosed in a protective sheath, used to carry current between points in an installation. Size is chosen according to current rating and voltage.

A standard number expressing the diameter or cross-sectional area of a wire, which determines its current-carrying capacity. Larger cross-section carries more current with less voltage drop.

The maximum current a device, cable, or protective component can carry continuously under stated conditions without exceeding its safe temperature rise.

A switch with three terminals that allows a lamp to be controlled from either of two positions, commonly used for staircases and long corridors.

A current that reverses direction periodically, usually in a sinusoidal pattern. In India the supply alternates at 50 hertz, completing fifty cycles each second.

A current that flows in one direction only, with constant magnitude in an ideal case. Batteries, solar cells, and rectified supplies provide direct current.

The number of complete cycles of an alternating quantity per second, measured in hertz. Indian grid supply is standardised at 50 hertz.

A static device that transfers electrical energy between two coils through mutual induction, changing voltage level while keeping frequency the same. It works only on alternating current.

An AC motor in which current in the stator winding produces a rotating magnetic field that induces currents in the rotor, causing it to turn below synchronous speed.

The difference between the synchronous speed of the rotating magnetic field and the actual rotor speed of an induction motor, usually expressed as a fraction of synchronous speed.

A set of conductors carrying bulk electrical power at high voltage from generating stations to substations, reducing current and therefore line losses over long distances.

The network of feeders, transformers, and service lines that delivers power from substations to individual consumers at usable voltage levels.

A circuit, often using diodes, that converts alternating current into direct current. It is found in battery chargers, adapters, and power supplies.

A two-terminal semiconductor device that conducts current mainly in one direction, acting as a one-way valve. It is used for rectification and protection.

A four-layer semiconductor switch that starts conducting when a gate pulse is applied and continues until current falls below a holding value. It is used for power control.

A semiconductor device that converts light energy directly into electrical energy through the photovoltaic effect. Many cells are connected to form a module or panel.

Energy obtained from sources that are naturally replenished, such as sunlight, wind, water, and biomass. It contrasts with finite fossil fuels.

The practice of reducing energy waste through efficient devices, better habits, and improved design, so the same work is done with less energy consumed.

An instrument that measures and records the electrical energy consumed by a consumer over time, usually displayed in kilowatt-hours for billing purposes.

A test instrument combining functions to measure voltage, current, and resistance. Digital versions display readings numerically and are widely used in fault finding.

An instrument that applies a high DC voltage to check the quality of insulation between conductors and earth, giving readings in megohms to reveal leakage paths.

A workshop joining process in which a low-melting filler alloy is melted to connect metal surfaces, commonly used for electrical joints and circuit board assembly.