Ø
The reduction of battery
capacity at high rates of discharge is primarily due to the rapid formation of lead
sulphate on the cell plates.
Ø
The time taken by an
alternating quantity to complete one cycle is called its time period (T).
(e.g. 50-Hz alternating current has a time period of 1/50 second)
Ø
The number of
cycles/second is known as the frequency of the alternating quantity. Its
unit is hertz (Hz).
Ø
The maximum value,
positive or negative, of an alternating quantity is known as its amplitude.
Ø
The r.m.s. value
of an AC is given by that steady (DC) current which when flowing through a
given circuit for a given time produces the same heat as produced by the AC
when flowing through the same circuit for the same time.
Ø
For the symmetrical
sinusoidal current, r.m.s. value is 0.707 × maximum value
of current.
Ø
The r.m.s. value of a
complex current wave is equal to the square root of the sum of the squares
of the r.m.s. values of its individual components.
Ø
Average value of current
is 0.637 × maximum value of current.
Ø
R.M.S. value is always
greater than average value except in the case of a rectangular wave when both
are equal.
Ø
Form factor is defined
as the ratio of r.m.s value / average value (i.e. 1.11)
Ø
Vectors are a shorthand
for the representation of alternating voltages and currents and their use
greatly simplifies the problems in AC work.
Ø
Various forms or methods
of representing vector quantities are Symbolic Notation, Trigonometrical Form,
Exponential Form and Polar Form.
Ø
Power Factor may be
defined as the cosine of the angle of lead or lag.
Ø
Power Factor may be
defined as the ratio of resistance / impedance (R/Z).
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