AC Fundamentals – Notes

Electrical Engineering » Notes » AC Fundamentals

Generation of Alternating Voltages and Currents

Alternating voltage may be generated by rotating a coil in a magnetic field, or by rotating a magnetic field within a stationary coil.

The value of the voltage generated depends, in each case, upon the number of turns in the coil, strength of the field and the speed at which the coil or magnetic field rotates. Alternating voltage may be generated in either of the two ways.


One complete set of positive and negative values of alternating quantity is known as cycle. Hence, each diagram of Fig. 11.6 represents one complete cycle.

A cycle may also be sometimes specified in terms of angular measure. In that case, one complete cycle is said to spread over 360or 2π radians.

Time Period

The time taken by an alternating quantity to complete one cycle is called its time period T. For example, a 50-Hz alternating current has a time period of 1/50 second


The number of cycles/second is called the frequency of the alternating quantity. Its unit is hertz (Hz).

It may be noted that the frequency is given by the reciprocal of the time period of the alternating quantity.

f = 1/T or T = 1/f


The maximum value, positive or negative, of an alternating quantity is known as its amplitude.


The fraction of the time period of that alternating current which has elapsed since the current last passed through the zero position of reference.

Root-Mean-Square (R.M.S.) Value

The r.m.s. value of an alternating current is given by that steady (d.c.) current which when flowing through a given circuit for a given time produces the same heat as produced by the alternating current when flowing through the same circuit for the same time.

Average Value

The average value of an alternating current is expressed by that steady current which transfers across any circuit the same charge as is transferred by that alternating current during the same time.

Form Factor

It is defined as the ratio, K­= r.m.s. value/average value = 0.707 m /0.637 I­= 1.1 (for sinusoidal alternating currents only).

In the case of sinusoidal alternating voltage also, Kf = 0.707 ­Em /0.637 E­= 1.1 (for sinusoidal alternating currents only).

Crest or Peak or Amplitude Factor

It is defined as the ratio a maximum value/r.m.s. value
m /(I­/√2) = √2 = 1.414 (for sinusoidal a.c. only).

For sinusoidal alternating voltage also, = IEm /(E/√2) = √2 = 1.414 (for sinusoidal a.c. only).

Subject Name : Electrical Engineering
Posts Name : Assistant Engineer, Management Trainee, Junior Engineer, Technical Assistant
Electrical Engineering Books

Objective Electrical Technology (2018-19 Session)
V.K Mehta (Author); English (Publication Language); 1089 Pages - 11/30/2004 (Publication Date) - S Chand (Publisher)
₹ 546
An Integrated Course in Electrical Engineering
J.B. Gupta (Author); English (Publication Language); 1100 Pages - 01/01/2013 (Publication Date) - S.K. Kataria & Sons (Publisher)
₹ 1,049
Basic Electrical Engg
Binding: paperback; Language: english; This product will be an excellent pick for you; V.K Mehta (Author)
₹ 620
Basic Electrical Engineering Revised First Edition
Product Condition: No Defects; Kulshreshtha, D C (Author); English (Publication Language); 880 Pages - 07/01/2017 (Publication Date) - McGraw Hill Education (Publisher)
₹ 275
A Handbook for Electrical Engineering(Old Edition)
ME Team (Author); English (Publication Language); 692 Pages - 01/01/2015 (Publication Date) - Made Easy Publications (Publisher)
₹ 267

GATE 2023 Total InfoENGG DIPLOMAUGC NET Total Info
IES 2023 Total InfoPSUs 2022 Total InfoCSIR UGC NET Total Info
JAM 2023 Total InfoM TECH 2023 Total InfoRAILWAY 2022 Total Info

Related Posts

  • Voltage, Current and Resistance - 105555555555 10. An ammeter is an electrical instrument used to measure ________. (a) current (b) voltage (c) resistance (d) none of the above
    Tags: voltage, current, electrical, basic, engineering
  • AC Fundamentals - 8AC Fundamentals » Exercise - 1 8. For a frequency of 200 Hz, the time period will be ________. (a) 0.05 s (b) 0.005 s (c) 0.0005 s (d) 0.5 s
    Tags: time, period, basic, electrical, engineering
  • Voltage, Current and Resistance - 135555555555 13. An ohmmeter is an instrument for measuring ________. (a) current (b) voltage (c) resistance (d) wattage
    Tags: voltage, current, basic, electrical, engineering
  • Voltage, Current and Resistance - 115555555555 11. A thermistor is a type of ________. (a) switch (b) resistor (c) battery (d) power supply
    Tags: voltage, current, basic, electrical, engineering
  • AC Fundamentals - 615555555555 61. A sinusoidal current has an rms value of 14 mA. The peak-to-peak value is ________. (a) 45.12 mA (b) 16 mA (c) 39.6 mA (d) 22.6 mA
    Tags: sinusoidal, current, basic, electrical, engineering


Please enter your comment!
Please enter your name here