EM Induction.........................pdf

CsNHS Senior High School
Caestebanan National High School
What is Electromagnetic Induction?
refers to the generation of an electric current
by passing a metal wire through a magnetic
field.
When an induced current is produced because of
voltage production (E.M.F) due to a changing
magnetic field, it is called electromagnetic induction.

What is Electromagnetic Induction?

Brief History of EM Induction
In 1820, Hans Christian
Oersted first discovered that
a magnetic field is always
associated with an electric
current.

Brief History of EM Induction
In August 29, 1831,
Michael Faraday discovered
electromagnetic induction
by his famous induction ring
experiment.

Characteristics of EM Induction
For movements between magnetic bar and the conductor, there
will be deflections in galvanometer.
If the bar and the conductor remain steady then there will be no
deflections in the galvanometer.
If the pole of the magnetic bar is changed, the direction of
induced current will change.
When the loops in the coil increases the deflection become
greater and when loops decreases the deflection become
smaller.

Magnetic Flux
The flux of the magnetic field
through a surface is defined in a
similar manner as we defined flux in
the electric field.

Magnetic Flux
Wb)
or Weber(
Tm
:
Unit
cos
2

BA
A
B
B
B






Magnetic Flux
The SI unit of magnetic flux is the weber (Wb) (in
derived units: volt-seconds), and the CGS unit is
the Maxwell.

Faraday’s
Experiments on
EM Induction

Faraday’s Experiment on EM Induction
He used a coil of wire,
galvanometer, and a bar magnet,
by noticing deflections he
conducted his first experiment.

He replaced the magnet bar with
a current carrying solenoid to
perform his second experiment.

He placed two coils close
together face to face but at rest
with respect to each other and by
closing and opening the circuit he
conducted his third experiment.

Faraday’s Experiment

wire
of
turns
#
)
cos
(









N
t
BA
N
t
N B 


Laws on
Electromagnetic
Induction

Faraday’s Law
It states that, the E.M.F induced in a wire is
proportional to the rate of the flux through the
loop.

Lenz’s Law
The induced E.M.F acts to the circulate a current in
a direction that oppose the change in flux which
caused the induced E.M.F

Lenz’s Law
Lenz's law gives the direction of the induced emf and
current resulting from electromagnetic induction.
The law provides a physical interpretation of the
choice of sign in Faraday's law of induction,
indicating that the induced emf and the change in
flux have opposite signs.

Lenz’s Law
t
N B





Lenz’s Law

Lenz’s Law
According to Lenz’s law, the
direction of included current
in a coil is such that it always
opposes the cause which
produces it.

Self-Induction
When the main current in the coil
decreases, the induced current
opposes the decay of current in
the coil.
increases, the induced current
opposes the growth of current in
the coil.

Mutual-Induction
decreases, induced current
developed in the neighboring coil
opposes the decay of current in the
coil.
increases, the induced current
developed in the neighboring coil
opposes the growth of current in the
coil

Lenz’s Law and Faraday’s Law
t
N B






Neumann’s Law
The magnitude of the induced E.M.F is
proportional to the rate of change of the magnetic
flux linking the circuit.

Application of
Electromagnetic
Induction

Induction Sealing
• Induction sealing is the process
of bonding thermoplastic
materials by induction heating.
This involves controlled heating
an electrically conducting object
(usually aluminum foil)
by electromagnetic induction,
through heat generated in the
object by eddy currents.
• Induction sealing is widely used to seal
capped:
– Sauces
– Dressings
– Ketchup
– Mustard
– Seasonings
– peanut butters
– Snacks
– Nuts
– Pretzels
– Powdered drinks
– Teas
– Sports drinks
– Coffees
– Teas
– Orange juice
– Milk

Induction Sealing

Induction Motor
•are electric motors that use alternating current (AC),
propelled by a magnetic field that rotates. They are made
up of a rotor, a stator and coils that convert electrical
energy into mechanical energy using electromagnetic
induction.
•AC induction motors are highly efficient and flexible, and
relatively simple in design, which allows them to match
the load demand for almost any electrical application.

Transformer
Probably one of the greatest inventions of
all time is the transformer. AC Current
from the primary coil moves quickly BACK
and FORTH (thus the idea of changing!)
across the secondary coil. The moving
magnetic field caused by the changing
field (flux) induces a current in the
secondary coil.

Microphone
A microphone works when sound waves
enter the filter of a microphone. Inside
the filter, a diaphragm is vibrated by the
sound waves which in turn moves a coil
of wire wrapped around a magnet. The
movement of the wire in the magnetic
field induces a current in the wire. Thus
sound waves can be turned into
electronic signals and then amplified
through a speaker.

Generators
AC Generators use Faraday’s law to
produce rotation and thus convert
electrical and magnetic energy into
rotational kinetic energy. This idea can
be used to run all kinds of motors. Since
the current in the coil is AC, it is turning
on and off thus creating a CHANGING
magnetic field of its own. Its own
magnetic field interferes with the shown
magnetic field to produce rotation.

Wireless Charging

Word Problem #1
A coil with 200 turns of wire is wrapped on an 18.0 cm square frame. Each
turn has the same area, equal to that of the frame, and the total
resistance of the coil is 2.0W . A uniform magnetic field is applied
perpendicularly to the plane of the coil. If the field changes uniformly
from 0 to 0.500 T in 0.80 s, find the magnitude of the induced emf in the
coil while the field has changed as well as the magnitude of the induced
current.

Word Problem #1












I
I
IR
x
t
BA
N
t
N B
)
2
(
80
.
0
90
cos
)
18
.
0
18
.
0
)(
0
500
.
0
(
200
cos






EM Induction.........................pdf

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EM Induction.........................pdf