Transcript 22-6,7,9

C H A P T E R 22
Electromagnetic Induction
Chapter 22
Electromagnetic Induction
•Induced emf and Induced current
•Motional emf
•Magnetic flux
•Faraday’s law of electromagnetic induction
•Lenz’s law
•Applications: cruise control, ground fault interrupter,
induction stove, electric guitar, microphone, & speaker.
•Electric generator
•Inductance
•Transformers and electric power transmission
22.6 Applications of
Electromagnetic Induction
The Magnetic Playback Head of a
Tape Deck
A Moving Coil Microphone.
22.7 The Electric Generator
Electric generators such as these supply electrical power by
producing an induced emf according to Faraday's law of
electromagnetic induction.
Electric
Generator
Emf of the Generator
The induced emf is given by the following equation where, N
is the number of turns in the coil, B is the magnetic field, A is
the area of the coil, and ω is the angular velocity of the
rotation of the coil.
  NBA ( Sin ( )(t )).
Self-inductance (L)
The alternating current in the coil generates an alternating
magnetic field that induces an emf in the coil.
The effect in which a changing current in a circuit induces an
emf in the same circuit is referred to as self-induction.
Unit of Inductance
The inductance, L is measured in henries. The magnitude of
L depends on the geometry of the coil and on the core
material.
By wrapping the coil around a ferromagnetic (iron) core, the
magnetic flux and therefore the inductance can be increased
substantially relative to that for an air core.
Because of their self-inductance, coils are known as
inductors and are widely used in electronics.
Inductors come in all sizes, typically in the range between
millihenries and microhenries.
22.9 Transformers
A transformer is a device for increasing or decreasing an ac
voltage.
A transformer consists of a primary coil and a secondary coil, both
wound on an iron core. The changing magnetic flux produced by
the current in the primary coil induces an emf in the secondary
coil. At the far right is the symbol for a transformer.
Power Transmission
Transformers play a key role in the transmission of
electric power.
Transformer
A transformer consists of two coils, a primary and a secondary,
wound around a soft iron core
The two coils are linked by the magnetic field.
The soft iron core will provide a medium by which the
magnetic flux from the primary coil is transferred to the
secondary coil.
Transformers are designed so that nearly all the magnetic flux
from the primary coil is transferred to the secondary coil.
Transformer Equations
Using Faraday’s law we can write expressions for the
primary and secondary voltages as follows.

VS  N S
.
t

VP  N P
.
t
Dividing the above equations we get,
VS
NS

.
VP
NP
Assuming that there is no power loss, we can write,
VS I S  V P I P .
VS I P N S


.
VP I S N P
Power Loss in Transmission Lines
PLoss  I R
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