Introduction to AC Circuits

INTRODUCTION TO AC CIRCUITS

Alternating voltage is generated by rotating a coil in a stationary magnetic field. It also be generated by rotating a magnetic field within a stationary coil. Rotating field method is used for generation of alternating voltage.

Sinusoidal Alternating Quantity

An alternating quantity which varies according to sine of the angle 9 is known as sinusoidal alternating quantity

(i) The sinusoidal voltage and currents produces low iron and copper losses in AC rotating machines and transformers. It improves the efficiency.

(ii) Sinusoidal voltage and current will offer less interference to nearby telephone lines.

(iii) They produce less disturbance in the electrical circuit.

The standard form of sinusoidal voltage

e = E_m sin ωt = E_m sin Ɵ

The standard form of sinusoidal current

i = I_m sin ωt=I_m sin Ɵ

Sinusoidal voltage waveform is shown in fig 1.24

Cycle:

It is a set of positive and negative portions of waveform.

Time period (T):

The time required for an alternating quantity to complete one cycle is called

time period.

Frequency (f):

The number of cycles occurring per second is called frequency.

Frequency, f = 1/T

Unit of frequency is Hertz (or) Cycles/second

Amplitude

The maximum value, positive or negative of the alternating quantity is called amplitude.