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Alternating Current Basics
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An alternating quantity (current i or voltage V) is one whose magnitude changes continuously with time between zero and a maximum value and whose direction reverses periodically.
Some graphical representation for alternating quantities
Equation of Alternating Quantities (i or V).
When a coil is rotated rapidly in a strong magnetic field, magnetic flux linked with the coil changes. As a result an emf is induced in the coil and induced current flows through the circuit. These voltage and current are known as alternating voltage and current
(1) Equation : Alternating current or voltage varying as sine function can be written as
i = i0 sinwt = i0 sin 2πn t = i0sin (2p / T)t
and V=V0 sin wt = V0 sin 2pvt = V0 sin (2p/ T) t
where i and V = Instantaneous values of current and voltage,
i0 and V0 = Peak values of current and voltage
w = Angular frequency in rad/sec, n = Frequency in Hz and T = time period
(2) About cycle
(i) The time taken to complete one cycle of variations is called the periodic time or time period.
(ii) Alternating quantity is positive for half the cycle and negative for the rest half. Hence average value of alternating quantity (i or V) over a complete cycle is zero.
(iii) Area under the positive half cycle is equal to area under negative cycle.
(iv) The value of alternating quantity is zero or maximum 2n times every second. The direction also changes 2n times every second.
(v) Generally sinusoidal waveform is used as alternating current/voltage.
(vi) At t=(T/4) from the beginning, i or V reaches to their maximum value..
Note : If instantaneous current i (or voltage V) becomes 1/n times of it's peak value in time t then t= (T/2p) sin-1 (1/n) second.
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