CIRCUITS 2- Topic 1&2

Alternating wave

A wave that varies in magnitude and direction periodically.

Amplitude

The maximum value (either positive or negative) which an alternating quantity attains during one complete cycle.

Altration

Equal to one-half of a cycle.

Frequency

Number of cycles made per second, unit is Hertz (Hz).

Time period

Time in seconds needed by an alternating quantity to complete one cycle.

Wavelength

Length of one complete cycle.

Direct Current (DC)

IT is the flow of electric charge in only one direction. It is the steady state of a constant-voltage circuit.

Alternating Current (AC)

It is the flow of electric charge that periodically reverses direction. If the source varies periodically, particularly sinusoidally.

Resistor

It takes a current that is in-phase with voltage across it. In a purely resistive load of an ac circuit, the current and voltage will both reach their maximum or peak values and fall through zero at exactly the same time, i.e. they rise and fall simultaneously and are therefore said to be “IN-PHASE ”.

Ideal Inductor

It takes a current that lags the voltage across it by 90°. In a purely inductive load of an AC Circuit, the applied voltage reaches its maximum positive value a quarter ( 1/4 ) of a cycle earlier than the current reaches its maximum positive value, in other words, the current “LAGS” the voltage by one quarter of a cycle or 90° as shown in the vector diagram.

Ideal Capacitor

It takes a current that leads the voltage across 90°. In a purely capacitive load of an AC Circuit, the applied voltage reaches its maximum positive value a quarter ( 1/4 ) of a cycle later than the current reaches its maximum positive value, in other words, the current “LEADS” the voltage by one quarter of a cycle or 90° as shown in the vector diagram.

Reactance

It is the opposition of a circuit element to the flow of current due to that element's inductance or capacitance.

Angular Velocity

This is the rate of change of angular displacement with respect to time. It is found by combining the resistance, capacitance and inductance.It is a measurement of the rate of change of angular position of an object over a period of time. It is denoted by ω. It is a vector quantity.

Impedance

It is found by combining the resistance, capacitance and inductance.

Active or Real Power (P)

The average value of the instantaneous power over one cycle of the voltage. The effective power that does real work.

Reactive Power (Q)

The circulating power, Q, in the circuit, measured in volt-amperes reactive. Power which does no real work.

Apparent Power (S)

The complex power, S, associated with the voltage phasor and the conjugate of the current phasor.

Power Factor (pf)

• Ratio of the active power, P, and the apparent power, S

• Expressed as a decimal number without unit or as a percentage

• Can never be greater than unity or 1

• Cosine of the angle between the voltage and current