Tamil Nadu HSE Second Year Basic Electrical Engineering 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 done per unit charge in moving charge between two points in a circuit, measured in volts. It is the electrical pressure that drives current through a conductor.

Electromotive force is the energy per unit charge supplied by a source such as a cell or generator to drive current around a complete circuit, measured in volts.

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

A property of a material expressing how strongly it resists current, equal to the resistance of a unit cube of that material. It is measured in ohm-metres.

For a conductor at constant temperature, the current through it is directly proportional to the potential difference across it, so V equals I multiplied by R.

The total current entering a junction in a circuit equals the total current leaving it, because charge cannot accumulate at a node. It expresses conservation of charge.

Around any closed loop of a circuit, the algebraic sum of all potential differences and EMFs is zero. It expresses conservation of energy in a network.

A connection in which components are joined end to end so the same current passes through each. Total resistance is the sum of the individual resistances.

A connection in which components are joined across the same two points so each has the same potential difference. The total current is the sum of branch currents.

The resistance inside a source such as a cell or battery that causes its terminal voltage to fall below its EMF when current is drawn, wasting energy as heat.

The potential difference actually available at the output terminals of a source while it supplies current, equal to the EMF minus the voltage drop across internal resistance.

The ability of a component to store electric charge per unit potential difference across it, measured in farads. One farad stores one coulomb at one volt.

A component made of two conducting plates separated by an insulator, which stores energy in the electric field between the plates when a voltage is applied.

An insulating material placed between the plates of a capacitor. It increases capacitance by a factor called the relative permittivity and also supports a higher working voltage.

Capacitors in series carry equal charge and their reciprocals add; capacitors in parallel share the same voltage and their capacitances add directly, opposite to resistor rules.

The energy held in a charged capacitor equals half the capacitance multiplied by the square of the voltage, and is stored in the electric field between the plates.

The total number of magnetic field lines passing through a given area, measured in webers. Flux density is flux per unit area perpendicular to the field.

The magnetic flux passing through unit area perpendicular to the field, measured in teslas or webers per square metre. It indicates the strength of the magnetic field.

The EMF induced in a coil equals the rate of change of magnetic flux linkage through it. Faster flux changes or more turns give a larger induced voltage.

The direction of an induced EMF is such that it opposes the change in flux producing it. This is a consequence of conservation of energy and explains back EMF.

The property of a coil by which a changing current in it induces an EMF in the same coil that opposes the change, measured in henries.

The total opposition a circuit presents to alternating current, combining resistance and reactance. It is measured in ohms and depends on frequency.

The opposition to alternating current caused by inductance or capacitance alone, measured in ohms. Inductive reactance rises with frequency while capacitive reactance falls.

The ratio of real power to apparent power in an AC circuit, equal to the cosine of the phase angle between voltage and current. Low values increase current for the same power.

The condition in a circuit containing inductance and capacitance where their reactances are equal and cancel, leaving impedance purely resistive and current at a maximum.

A system of three alternating voltages of equal magnitude and frequency, displaced by 120 electrical degrees, which delivers constant power and suits large motors.

A three-phase connection in which one end of each phase winding is joined at a common neutral point. Line voltage is root three times the phase voltage.

A three-phase connection in which windings form a closed triangle. Line voltage equals phase voltage and line current is root three times phase current.

A static device with two windings on a common magnetic core that transfers AC energy between voltage levels by mutual induction, with no change in frequency.

The ratio of primary to secondary turns of a transformer, which fixes the ratio of primary to secondary voltage and the inverse ratio of currents.

Energy wasted as heat by circulating currents induced in the core of a magnetic device. It is reduced by laminating the core or using ferrite material.

Energy wasted each cycle as the core of a magnetic device is repeatedly magnetised and demagnetised. It is reduced by using a material with a narrow hysteresis loop.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a percentage of synchronous speed. Slip is zero at no load.

The speed of the rotating magnetic field in an AC machine, equal to 120 times the supply frequency divided by the number of poles, in revolutions per minute.

Deliberately connecting exposed metalwork or a circuit point to the general mass of earth so fault current flows safely and protective devices operate quickly.

A protective device containing a metal element that melts and breaks the circuit when current exceeds its rating for a set time, isolating the faulty section.

A resettable automatic switch that trips on overload or short circuit using thermal and magnetic elements, replacing a fuse in modern distribution boards.

A protective device that trips when it detects a small difference between live and neutral current, indicating leakage to earth, protecting people from electric shock.

A measuring instrument in which a coil carrying current rotates in a permanent magnetic field. It reads average values and suits direct current measurements.

A measuring instrument in which a soft iron piece is attracted or repelled by the field of a fixed coil. It responds to both AC and DC and reads root mean square values.

A low resistance connected in parallel with an ammeter movement to bypass most of the current, extending the range of the instrument to measure larger currents.

A high resistance connected in series with a voltmeter movement to limit current through it, allowing the instrument to measure higher voltages without damage.

The quantity of charge a cell or battery can deliver before needing recharge, usually stated in ampere-hours at a specified discharge rate and temperature.

A secondary cell with lead peroxide and sponge lead electrodes in dilute sulphuric acid, giving about two volts per cell and widely used in vehicles and inverters.

A circuit using diodes that converts alternating current into unidirectional current, forming the first stage of most DC power supplies.

A diode designed to operate safely in reverse breakdown at a fixed voltage, used to provide a stable reference or to regulate the output of a power supply.

A network of capacitors and inductors placed after a rectifier to smooth the pulsating DC output into a steadier voltage with less ripple.

A set of conductors and supporting structures carrying bulk electrical power at high voltage from generating stations to distribution centres over long distances.

The tendency of alternating current to concentrate near the surface of a conductor, raising effective resistance at high frequency and in thick conductors.

A visible violet glow with hissing sound caused by ionisation of air around high-voltage conductors, wasting power and requiring larger conductor spacing.