Karnataka SSLC Elements of Electrical Engineering IV - JTS (KSEAB) 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.

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. It is not a mechanical force despite the name.

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.

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

A property of a material expressing how strongly it resists current, quoted in ohm-metres. Copper has low resistivity, so it is used for conductors; nichrome has high resistivity, so it is used for heating elements.

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

A circuit in which components are connected across the same two points, so each has the full supply voltage and the current divides between branches. Total resistance is always less than the smallest branch resistance.

Two rules for solving networks: the current law says charge entering a junction equals charge leaving it, and the voltage law says the sum of voltage drops around any closed loop equals the applied voltage.

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

Power consumed over a period of time, measured in joules or, for billing purposes, in kilowatt-hours. One kilowatt-hour is the energy used by a one-kilowatt load running for one hour.

The resistance inside a source such as a cell or battery that causes its terminal voltage to fall below its electromotive force when current is drawn. It also causes heating within the source.

The total number of magnetic field lines passing through a given area, measured in webers. It represents the quantity of magnetism present in a region.

The magnetic flux passing through unit area perpendicular to the field, measured in teslas or webers per square metre. It describes how concentrated the magnetic field is at a point.

A measure of how easily a material allows magnetic flux to pass through it. Ferromagnetic materials such as iron have high permeability, which is why they are used for transformer cores.

The opposition a magnetic circuit offers to magnetic flux, analogous to resistance in an electric circuit. It is high for air gaps and low for iron paths of large cross-section.

A statement that the electromotive force 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 rule that an induced current always flows in a direction whose magnetic effect opposes the change producing it. It explains the opposing force felt when a magnet is pushed into a coil.

The property of a coil by which a changing current in it induces a back electromotive force in the same coil, measured in henries. It opposes any change in current.

Energy wasted as heat each time the magnetic state of a core is reversed through a complete alternating cycle. It is reduced by using soft magnetic materials such as silicon steel.

Power lost as heat when circulating currents are induced within the body of a magnetic core by a changing flux. Laminating the core reduces these currents and the resulting loss.

The effective value of an alternating quantity, equal to the steady direct value that would produce the same heating effect. For a sine wave it is peak value divided by the square root of two.

The ratio of the root mean square value of an alternating quantity to its average value. For a pure sine wave it equals approximately 1.11.

The ratio of the maximum value of an alternating quantity to its root mean square value. For a sine wave it is approximately 1.414, useful when choosing insulation ratings.

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

The total opposition to alternating current from resistance and reactance combined, measured in ohms. It determines current when an alternating voltage is applied to a circuit.

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

The component of alternating power that actually does useful work and is converted to heat, light or motion, measured in watts. It equals voltage times current times power factor.

The power that oscillates between source and reactive load without doing net work, measured in volt-amperes reactive. It is needed to establish magnetic fields in motors and transformers.

A three-phase connection joining one end of each winding at a common neutral point. Line voltage is root three times phase voltage, while line current equals phase current.

A three-phase connection in which windings are joined end to end in a closed loop. Line current is root three times phase current, while line voltage equals phase voltage.

A static device that transfers electrical energy between two circuits at different voltages by mutual induction, with no change in frequency. It works only on alternating supply.

The number of turns on the secondary winding divided by the number on the primary. It sets the secondary voltage relative to primary voltage and inversely relates the currents.

The voltage induced in a running motor's armature that opposes the applied supply voltage. It limits armature current, so a motor with no load draws very little current.

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 and increases with load.

The speed of the rotating magnetic field in an alternating machine, equal to 120 times the supply frequency divided by the number of poles. A four-pole motor on fifty hertz runs at 1500 revolutions per minute.

A rugged alternating-current motor in which a rotating field induces currents in a short-circuited rotor, producing torque without brushes or slip rings. It is the most common industrial drive.

Deliberately connecting exposed metalwork or the neutral point to the general mass of earth through a low-resistance path, so fault current trips protection and touch voltage stays safe.

A resettable protective device that automatically opens a circuit on overload or short circuit using thermal and magnetic elements. Its rating is chosen to protect the cable downstream.

A device that trips when the current difference between live and neutral conductors exceeds a set value, indicating leakage to earth. It protects people from electric shock.

An instrument that integrates power over time and records the kilowatt-hours consumed, forming the basis of electricity billing. Induction types use a rotating aluminium disc.

The schedule of charges a supply authority applies for electrical energy, often combining a fixed charge, an energy rate per unit and sometimes a maximum demand charge.

The practice of connecting capacitors in parallel with inductive loads to reduce the phase angle, lowering current drawn and avoiding utility penalties for poor power factor.

Using less energy for the same useful output through efficient lamps, motors, controls and operating habits, cutting both electricity bills and environmental impact without reducing comfort.