Definition
- Alternating current(AC)-
It is a type of electrical current, in which the direction of the flow of electrons switches back and forth at regular intervals or cycles. Current flowing in power lines and normal household electricity that comes from a wall outlet is alternating current. The standard current used in the U.S. is 60 cycles per second (i.e. a frequency of 60 Hz); in Europe and most other parts of the world it is 50 cycles per second (i.e. a frequency of 50 Hz.).
It is a electrical current which flows consistently in one direction. The current that flows in a flashlight or another appliance running on batteries is direct current.
One advantage of alternating current is that it is relatively cheap to change the voltage of the current. Furthermore, the inevitable loss of energy that occurs when current is carried over long distances is far smaller with alternating current than with direct current.
Graphic representation of the intensity of the current as a function of time:-
Basic parameter of alternating current:-
They are-
a.Amplitude
b.Frequency
c.Wavelength
d.Peak to Peak value
e.Root Mean Square (RMS) Value
f.Average Value
a. Amplitude- The maximum positive or negative value attained by an alternating quantity in one complete cycle is called Amplitude or peak value or maximum value. The maximum value of voltage and current is represented by Em or Vm and Imrespectively.
b.Frequency- The number of cycles made per second by an alternating quantity is called frequency. It is measured in cycle per second (c/s) or hertz (Hz) and is denoted by (f).
c.Wavelength- The total distance covered by sound wave per unit time. Thus, it is a measurement of distance between two identical peak (high points) or through (low points) in a wave.
d. Peak to Peak value- It is the differences between the maximum positive and the maximum negative amplitude of a wave form.
e. Root Mean Square (RMS) Value- It is that steady current when passed through a resistance for a given time produces the same amount of heat as the alternating current does in the same resistance in the same time.
The r.m.s. value or virtual value or effective value of a.c. is 0.707 times the peak value of a.c.
f.Average Value- Alternating current is positive during the first half cycle and negative during another half cycle, so the mean average value of a.c. over one cycle is zero.
The average value of a sine wave of voltage or current is 0.637 times the peak value, (Vp or Ip). This mathematical relationship between the average values, applies to both AC current and AC voltage.
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