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UNIT-II
Alternating Quantities
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Principle of AC voltage: Consider a rectangular coil of N turns placed in a uniform magnetic field as shown in
the figure. The coil is rotating in the anticlockwise direction at an uniform angular velocity of ω rad/sec
When the coil is in the vertical position, the flux linking the coil is zero because the plane of the coil is parallel
to the direction of the magnetic field. Hence at this position, the emf induced in the coil is zero. When the coil
moves by some angle in the anticlockwise direction, there is a rate of change of flux linking the coil and
hence an emf is induced in the coil. When the coil reaches the horizontal position, the flux linking the coil is
maximum, and hence the emf induced is also maximum. When the coil further moves in the anticlockwise
direction, the emf induced in the coil reduces. Next when the coil comes to the vertical position, the emf
induced becomes zero. After that the same cycle repeats and the emf is induced in the opposite direction.
When the coil completes one complete revolution, one cycle of AC voltage is generated. The generation of
sinusoidal AC
Voltage can also be explained using mathematical equations. Consider a rectangular coil of N turns placed in a
uniform magnetic field in the position shown in the figure. The maximum flux linking the coil is in the
downward direction as shown in the figure. This flux can be divided into two components, one component
acting along the plane of the coil Φmaxsinωt and another component acting perpendicular to the plane of the coil
Φmaxcosωt.
ω rad/sec
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, Smartzworld.com Smartworld.asia
θ
x
Фmaxsinωt
Фmaxcosωt
Фmax
The component of flux acting along the plane of the coil does not induce any flux in the coil. Only the
component acting perpendicular to the plane of the coil ie Φmaxcosωt induces an emf in the coil.
Angular Frequency (ω)
Angular frequency is defined as the number of radians covered in one second(ie the angle covered by the
rotating coil). The unit of angular frequency is rad/sec.
Advantages of AC system over DC system
1. AC voltages can be efficiently stepped up/down using transformer
2. AC motors are cheaper and simpler in construction than DC motors
3. Switchgear for AC system is simpler than DC system
Definition of Alternating Quantity
e
+Em
0 π/2 π 3π/2 2π ωt
-EmT
jntuworldupdates.org Specworld.in
UNIT-II
Alternating Quantities
jntuworldupdates.org Specworld.in
,Smartzworld.com Smartworld.asia
Principle of AC voltage: Consider a rectangular coil of N turns placed in a uniform magnetic field as shown in
the figure. The coil is rotating in the anticlockwise direction at an uniform angular velocity of ω rad/sec
When the coil is in the vertical position, the flux linking the coil is zero because the plane of the coil is parallel
to the direction of the magnetic field. Hence at this position, the emf induced in the coil is zero. When the coil
moves by some angle in the anticlockwise direction, there is a rate of change of flux linking the coil and
hence an emf is induced in the coil. When the coil reaches the horizontal position, the flux linking the coil is
maximum, and hence the emf induced is also maximum. When the coil further moves in the anticlockwise
direction, the emf induced in the coil reduces. Next when the coil comes to the vertical position, the emf
induced becomes zero. After that the same cycle repeats and the emf is induced in the opposite direction.
When the coil completes one complete revolution, one cycle of AC voltage is generated. The generation of
sinusoidal AC
Voltage can also be explained using mathematical equations. Consider a rectangular coil of N turns placed in a
uniform magnetic field in the position shown in the figure. The maximum flux linking the coil is in the
downward direction as shown in the figure. This flux can be divided into two components, one component
acting along the plane of the coil Φmaxsinωt and another component acting perpendicular to the plane of the coil
Φmaxcosωt.
ω rad/sec
jntuworldupdates.org Specworld.in
, Smartzworld.com Smartworld.asia
θ
x
Фmaxsinωt
Фmaxcosωt
Фmax
The component of flux acting along the plane of the coil does not induce any flux in the coil. Only the
component acting perpendicular to the plane of the coil ie Φmaxcosωt induces an emf in the coil.
Angular Frequency (ω)
Angular frequency is defined as the number of radians covered in one second(ie the angle covered by the
rotating coil). The unit of angular frequency is rad/sec.
Advantages of AC system over DC system
1. AC voltages can be efficiently stepped up/down using transformer
2. AC motors are cheaper and simpler in construction than DC motors
3. Switchgear for AC system is simpler than DC system
Definition of Alternating Quantity
e
+Em
0 π/2 π 3π/2 2π ωt
-EmT
jntuworldupdates.org Specworld.in
