As you saw in an earlier lesson electrical
current can create a magnetic field.
Whenever current flows through a conductor
a magnetic field
consisting of flux lines builds up around
the conductor.
If the wire is straight the magnetic field
is extremely weak.
If the wire is coiled, the magnetic field
is concentrated and can be very strong.
This is Electromagnetism, the production of
a magnetic field by an electric current.
Current is made up of free electrons moving
in a coordinated direction in a wire.
Since each of the electrons has a magnetic
field, these fields combine
to produce a magnetic field or flux lines
around the wire.
When there is no current in the wire there
is no magnetic field
because the electrons in the wire revert to
random motion.
When this happens the individual magnetic
fields around the electrons cancel each other
out.
In addition to the ability of current to create
magnetism, you also
previously saw the ability of magnetism or
a magnetic field
to create an electromotive force in a conductor
without any physical contact.
This phenomenon is Electromagnetic Induction,
the production
of EMF in a conductor using a magnetic field.
When the conductor moves through the magnetic
field the flux lines
act on the molecules, especially the free
electrons in the conductor.
The free electrons are pushed in one direction
by the magnetic field
so that they move toward one end of the wire.
This end becomes
more negative than the other end causing an
emf or voltage
to be induced in the conductor.
If the ends of the conductor are connected
to a circuit an induced current flows.
Voltage is induced either by moving the magnet
so that its flux lines move
or cut through the conductor, or by moving
the conductor so that
it moves or cuts through the magnetic field.
This movement
when the flux lines are cut by the conductor,
or the conductor is cut by the flux lines
is called relative movement.
Without relative movement between
conductor and flux lines an emf will not be
generated.
Electromagnetic Induction, then is more properly
defined as
The production of EMF in a conductor when
relative movement
occurs between the conductor and the magnetic
field.
The amount of voltage produced by electromagnetic
induction
is determined by four 4 factors.
These factors were originally
stated by Michael Farraday, an English scientist
of the early 1800's.
Let's hear how he might have described it.
"The voltage induced in a conductor is directly
proportional to the
rate at which the conductor cuts the magnetic
lines of force."
This is now known as Faraday's Law.
From this Law we can derive the four different
ways to increase the
rate at which the conductor cuts the magnetic
lines of force.
The most obvious way is simply to speed up
the rate at which we
move the conductor through the magnetic field.
The faster the conductor moves through a magnetic
field, the
more lines get cut per second and more EMF
is produced.
The angle of the wire as it cuts into the
magnetic field also effects magnetic induction.
When the wire is at right angle to the lines
of force of the magnet
it will cut the maximum number of lines , but
if the wire conductor and
magnetic field at less or more than 93 angle,
less flux lines are cut
and if the flux lines and the conductor are
parallel to each other
no flux lines are cut and no emf gets generated.
Another way of increasing induced emf is to
use a longer wire.
A longer wire can be wound so that more loops
of wire can cut the magnetic field.
Finally, you can always increase emf by simply
having a stronger
magnetic field, in this case using a core
of iron to concentrate the flux lines.
Since the conductor cuts through more flux
lines at a time
the induced emf is increased.
Faraday's Law states that the induced voltage
is affected by four factors:
1.
The speed at which the flux lines are cut
2.
The length of the conductor cutting flux lines
3.
The angle at which the lines are cut
4.
Finally, the strength of the magnetic field,
or the number of flux lines that are cut.
Once again all of these factors affect the
voltage induced into an inductor.
the end.
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