Tamil Nadu HSE First Year Basic Electrical Engineering key terms

The rate at which electric charge flows through a conductor, measured in amperes (A). One ampere equals one coulomb of charge passing a point per second.

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

Electromotive force: the energy per unit charge supplied by a source such as a battery or generator to drive current around a circuit. It is measured in volts and is not a mechanical force.

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

A material property giving the resistance of a unit cube of that material, measured in ohm-metres (Ω·m). It allows comparison of materials independent of shape or size.

The reciprocal of resistance, representing how easily current flows through a component. It is measured in siemens (S), where one siemens equals one reciprocal ohm.

For a conductor at constant temperature, the current is directly proportional to the potential difference across it. It is expressed as V = IR, where V is volts, I amperes, and R ohms.

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 has the same voltage. Total resistance is less than the smallest branch resistance, and current divides among branches.

A series arrangement of resistors used to obtain a fraction of the supply voltage across one resistor. The output voltage equals supply voltage times that resistance divided by total series resistance.

A parallel arrangement of resistors in which the total current splits among branches. The current in one branch is inversely proportional to that branch's resistance.

The rate at which electrical energy is converted into another form, measured in watts (W). In a resistive circuit it equals voltage times current, or current squared times resistance.

The total work done by an electric circuit over time, measured in joules (J) or kilowatt-hours (kWh). One kilowatt-hour equals the energy used by a 1 kW load for one hour.

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

The total number of magnetic field lines passing through a given area, measured in webers (Wb). It describes the strength and extent of a magnetic field through a surface.

Magnetic flux per unit area perpendicular to the field, measured in teslas (T) or webers per square metre. It indicates how concentrated a magnetic field is at a point.

The region around a magnet or current-carrying conductor where magnetic forces act on other magnets or moving charges. Its direction is given by the north pole of a compass needle.

A rule stating that if you grip a current-carrying conductor with your right hand so the thumb points along the current, your curled fingers show the direction of the magnetic field around it.

A rule for motors: with the thumb, forefinger, and middle finger of the left hand mutually at right angles, the forefinger shows field, middle finger current, and thumb the force on the conductor.

A rule for generators: with the thumb, forefinger, and middle finger of the right hand mutually at right angles, the forefinger shows field, thumb motion, and middle finger induced current.

The production of an electromotive force in a conductor when it experiences a changing magnetic flux. This principle underlies generators and transformers.

The induced emf in a coil equals the rate of change of magnetic flux linkage through it. More turns or faster flux change produces a larger induced emf.

The direction of an induced emf is such that it opposes the change in magnetic flux that produced it. This law follows from conservation of energy.

A machine that converts mechanical energy into direct current electrical energy using electromagnetic induction. A commutator and brushes rectify the alternating emf produced in the armature.

A machine that converts direct current electrical energy into mechanical energy. Current in the armature interacts with the magnetic field to produce torque that rotates the shaft.

A segmented cylindrical switch on a DC machine armature that reverses the external circuit connections at the correct instants. It converts alternating armature emf into direct current output.

Carbon or graphite contacts that press against the commutator to carry current between the rotating armature and the external circuit. They wear gradually and need periodic inspection.

The emf induced in a motor's armature that opposes the applied voltage. It limits armature current and is proportional to speed, so it regulates motor operation.

Root-mean-square value of an alternating quantity: the equivalent steady direct current that produces the same heating effect. For a sine wave it equals peak value divided by the square root of two.

The maximum instantaneous value reached by an alternating quantity during one cycle. It is also called amplitude or crest value and is related to RMS value by the form factor.

The ratio of RMS value to average value of an alternating quantity. For a pure sine wave it equals approximately 1.11, and it indicates waveform shape.

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

The useful power actually consumed by a load in an AC circuit, measured in watts. It equals voltage times current times power factor for sinusoidal quantities.

The power that oscillates between source and reactive load without doing useful work, measured in volt-amperes reactive (var). It is associated with inductors and capacitors in AC circuits.

Connecting exposed metal parts of electrical equipment to the earth through a low-resistance path. It provides a safe route for fault current and protects users from electric shock.

A protective device containing a thin wire that melts and opens the circuit when current exceeds its rating. It protects conductors and equipment from overload and short-circuit damage.

A resettable protective switch that automatically opens a circuit under overload or short-circuit conditions. Unlike a fuse, it can be reset and reused after the fault is cleared.

The physiological effect of electric current passing through the human body, which can cause burns, muscle contraction, or cardiac arrest. Severity depends mainly on current magnitude and path.

A multi-range instrument that measures voltage, current, and resistance, and often continuity. It is a fundamental tool for testing and troubleshooting electrical circuits in the laboratory.

An instrument used to measure potential difference between two points, connected in parallel with the component. It has very high resistance so it draws negligible current.

An instrument used to measure electric current, connected in series with the circuit. It has very low resistance so it does not significantly alter the current being measured.

An instrument used to measure resistance of a component or circuit, with the component disconnected from any power source. It supplies a small internal current for the measurement.

An instrument that measures electrical power in watts, typically having a current coil and a voltage coil. In laboratories it is used to verify power calculations and load behaviour.