# R

## Reluctance

The opposition that a magnetic circuit presents to the passage of magnetic lines through it.

## Reactance

The opposition to the flow of an alternating current by an inductive or capacitive element in the circuit.

## Resistance

Resistance is defined as the measure of opposition to the motion of electrons due to their continuous collisions, with the atoms of the conductor

## Rheostat

A potentiometer or a rheostat is an instrument used to measure and compare potentials without drawing any current from the circuit.

## Retentivity

The ability of a magnetic material to retain its magnetism.

## Residual Magnetism

The magnetism remaining after the external magnetizing force is removed.

In a circle, the angle included within an arc equal to the radius of a circle. Numerically, the angle is 57.3o.

## RMS Value

The AC current value that develops the same heating effect as the corresponding DC current value. For sine wave currents, the RMS or effective value is 0.707 times the peak value.

## Resonance

It is the condition that happens when a circuit’s capacitive and inductive reactances are counterbalanced.

## Reactive power

The product of voltage and out-of-phase components of alternating current.

## Real power

The average power, or active power, or the real part of the complex power.

## Reluctance

It is the ratio of the magnetomotive force (MF) to the magnetic flux in a magnetic circuit.

## Reluctance power

The component of the power delivered by a synchronous generator representing the effects of generator saliency.

## Reset

The action of a relay as it makes designated responses to decreases in the input.

## Reset value

The maximum value of an input quantity reached by progressive decreases that will permit the relay to reach the state of complete reset from the pickup.

## Residual voltage

The generated voltage due to the residual ﬂux in the ﬁeld poles even when the ﬁeld circuit remains unexcited.

## Rotor

The rotating member of a machine, with the shaft.

## RPM

RPM is the abbreviation for Revolutions per Minute. This is usually the rotational speed of things like motors.

## Relay

A relay is an electromechanical device that can be used to control multiple loads with one control circuit.

## Reactive Power

A measure of an inductor’s ability to receive and return energy in a circuit.