LESSON NOTE for APPLIED ELECTRICITY

ALTERNATING CURRENT CIRCIUT THEORY 1 Generation of e.m.f in a single turn coil

POINTS Alternating current is current which charges both in magnitude and direction uniformly in series of fluction. An e.m.f is generated in the coil, which varies in magnitude and reverses its direction at regular intervals.

Definition of Terms The WAVEFORM of e.m.f produced by an alternator is called a sine wave and the mains electricity supply if of “sinusoidal form”. The CYCLE is the complete sequence of an alternating event. The PERIOD (T) is the time taken for an alternating quantity to complete one cycle T = 1/F = 2π/ω

Definition cont’d The FREQUENCY (F) is the number of cycles completed in one second. Its unit is Hertz(Hz) The Standard Frequency of the electricity supply in Nigeria is 50Hz. F = 1/T = ω/2π Instantaneous values are the values of the alternating quantities at an instant of time. They are represented by small letters; j,v,a etc. Peak Value, also known as amplitude or maximum value is the largest value reached in a half circle i.e. at the peak or crest of the waveform. Represented by capital letters; Q,P,R etc.

Definition cont’d A peak-to-peak value is the difference between the maximum and the minimum values in a cycle. Average/Mean Value is the area under half cycle divided by the length of the base. It is = × max. value Effective Value is that current which will produce the same heating effect as an equivalent direct current. It is also called the root mean square (r.m.s) value. It is = × max. value

Definition cont’d Form factor is the ratio of r.m.s value to the average value for any waveform i.e. form factor= r.m.s value/average value = 1.11 Peak Value = max. value/r.m.s value = 1/0.707 = 1.41 = √2

EVALUATION 1.What do you understand by the term A.C ? 2.Explain these terms as applied to A.C waveform a)max. value b)instantaneous values c)r.m.s values