Page 26 - Basics of Electrical, Electronic and Communication

62 Chapter 4. Single Phase AC Circuits

where E m and I m are peak values of induced emf and current re-
spectively and ω is the angular velocity of the coil given by

ω = 2πf

where f is the frequency in Hz.
From the expressions of emf and current, it is clear that instanta-
neous values of emf and current vary as the sine functions of angle θ.
So they are known as sinusoidal voltage and current. When the emf or
current is plotted against time, a sine wave as shown in Figure 4.3 is
obtained.
v

Vm
t

2π radians

Figure 4.3: Sine wave

θ = 90 ο
θ = 60 ο N S
N S

θ = 0 ο θ = 180 ο θ = 360 ο
N S N S N S

θ = 270 ο
N S

Figure 4.4: Position of coil and induced emf

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