Maharashtra HSC Electrical Technology (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 per second.

The work needed to move a unit positive charge between two points in a circuit, measured in volts. It is the electrical pressure that drives current through a conductor.

The opposition a material offers to the flow of electric current, measured in ohms. It depends on the material, its length, cross-sectional area, and temperature.

The relationship stating that current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, at constant temperature.

A property of a material expressing how strongly it resists current flow, measured in ohm-metres. It is independent of the conductor's shape or size.

The ability of a material to carry electric current, the reciprocal of resistivity. Metals such as copper and aluminium have high conductivity and are used for conductors.

A material containing free electrons that allows electric current to pass through it easily. Copper, aluminium, and silver are common examples used in wiring and cables.

A material that offers very high resistance to current flow because it has few free electrons. Rubber, PVC, porcelain, and glass are used to cover and support conductors.

The maximum voltage per unit thickness an insulating material can withstand without breaking down and conducting. It is usually expressed in kilovolts per millimetre.

The energy per unit charge supplied by a source such as a battery or generator to drive current around a circuit, measured in volts. It differs from terminal voltage by internal drop.

The resistance present inside a source of emf, such as a cell or generator, which causes its terminal voltage to fall as the current drawn increases.

The ratio of real power to apparent power in an AC circuit, equal to the cosine of the phase angle between voltage and current. A low value means poor utilisation.

The power actually consumed or converted into useful work in an AC circuit, measured in watts. It equals voltage times current times power factor in single-phase circuits.

The power that oscillates between source and reactive loads such as inductors and capacitors without doing useful work, measured in volt-amperes reactive. It is needed to sustain magnetic fields.

A static device that transfers electrical energy between two circuits at different voltage levels through mutual induction, with no change in frequency and very little loss.

The ratio of the number of turns in the secondary winding of a transformer to the number in the primary. It determines the step-up or step-down voltage relationship.

The production of an emf in one coil due to a changing current in a nearby second coil linked by magnetic flux. It is the operating principle of transformers.

An AC motor in which current is induced in the rotor by the rotating magnetic field of the stator, so no electrical connection to the rotor is needed. It is the most common industrial motor.

The speed of the rotating magnetic field produced by a stator winding, equal to 120 times the supply frequency divided by the number of poles. It is expressed in revolutions per minute.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a percentage of synchronous speed. The motor cannot run at exactly synchronous speed.

An instrument used to measure electric current, connected in series with the circuit. An ideal ammeter has very low resistance so that it does not disturb the current.

An instrument used to measure potential difference between two points, connected in parallel with the component. An ideal voltmeter has very high resistance to avoid drawing current.

A portable measuring instrument that combines functions such as voltage, current, and resistance measurement in one unit, usually with a digital display and a selector switch.

An instrument that records the total electrical energy consumed over time, usually in kilowatt-hours. It is the basis for domestic and industrial electricity billing.

A transformer used to step down a large alternating current to a small, safe value for measurement or protection. Its secondary must never be left open-circuited while energised.

Connecting exposed metal parts of an installation to the general mass of earth so that fault current flows safely to ground and protective devices operate quickly.

A metal rod or plate buried in the soil and connected to the earthing conductor, providing a low-resistance path to earth. Its resistance depends on soil type and moisture.

A protective device that trips when it detects a small imbalance between live and neutral currents, indicating leakage to earth. It protects people against electric shock.

An automatic switch that opens a circuit on overload or short circuit and can be reset manually. Its rating is chosen to protect the cable and connected equipment.

A protective device containing a metal element that melts and opens the circuit when current exceeds its rating for a set time, thereby protecting cables and equipment from damage.

An accidental low-resistance path between conductors at different potentials, causing a very large current to flow. It can damage equipment and start fires if not cleared quickly.

A condition in which a circuit or machine carries more current than its rated value for a prolonged period, causing excessive heating without necessarily being a short circuit.

The conductor that connects exposed conductive parts of equipment to the earth electrode, providing a low-impedance path for fault current. Its size is specified by wiring regulations.

The statutory regulations governing generation, transmission, supply, and use of electricity in India, covering safety, clearances, and installation requirements that electricians must follow.

A drawing that represents a three-phase power system using one line to show all phases, with symbols for generators, transformers, breakers, and feeders. It simplifies system representation.

A drawing that shows the electrical connections and functions of a circuit using standard symbols, without indicating the physical layout or size of components.

A drawing that shows the actual physical connections between components and their terminal numbers, used for assembling, tracing, and troubleshooting an installation.

A two-terminal semiconductor device that conducts current easily in one direction and blocks it in the reverse direction, used for rectification and protection.

A circuit that converts alternating current into direct current using diodes, either as a half-wave or full-wave arrangement, often followed by a filter capacitor.

A three-terminal semiconductor device used to amplify signals or act as an electronic switch. In bipolar types the terminals are emitter, base, and collector.

An electromagnetic switch in which a coil operates contacts to control a separate circuit. It allows a small control signal to switch a larger load safely.

A heavy-duty electromagnetic switch used to control power circuits such as motors, operated by a control coil and often combined with overload protection.

A component that stores electrical energy in an electric field between two plates separated by a dielectric, measured in farads. It is used for filtering, starting motors, and power factor correction.

A portable instrument that applies a high DC voltage to measure insulation resistance of cables, windings, and equipment, confirming that insulation is safe before energising.

A standard number indicating the cross-sectional area or diameter of a conductor, such as the metric square-millimetre size or the older SWG number. It determines current-carrying capacity.

The maximum current a conductor can carry continuously without its temperature exceeding the safe limit for its insulation, depending on material, size, and installation method.

The voltage at which an insulating material suddenly loses its insulating property and allows current to pass, often accompanied by arcing or permanent damage.