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# What is Electromagnetism?

Section (3.1)
by

## nahed abou aishe

on 17 May 2016

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#### Transcript of What is Electromagnetism?

What particle
in atoms produces
magnetic field?
The compass needle changed
its direction whenever a
current is produced
What is a
magnet and
magnetic field?
Compare the compasses before and after connecting the circuit
Electricity and magnetism are related
Whenever there is electricity
there is magnetism, which
is due to the current that
produces magnetic field
This relation
is electromagnetism
The magnetic field lines are
circular around a wire
How can you tell if there is current or no in a wire????
Check if the needle of the compass is pointing north
How can we specify the direction
of a magnetic field produced in a circuit???
Simply by using
"Right-hand rule"
Such field can be
turned on or off
Such magnetic field has 3 characteristcs
The direction of such
field can be reversed
The strength of such
field can be changed
by turning the
current on or off
by reversing the direction of the current
by twisting the wire into a loop
or coils
For sure these are not applicable
for the Earth's magnetic field
More loops or coils, field will
be stronger
So it's better to wind a wire with a current into many loops to strengthen the magnetic field in the center of the coil
What do we call a coil
of wire with current??
Solenoid
The magnetic field around a solenoid
resembles that of a bar magnet
If the wire is twisted into a loop the magnetic field lines become bunched up inside the loop stengthening the magnetic field in the center
but how is solenoid
different from a bar magnet?
The poles can be changed in a solenoid but not in a bar magnet by changing the direction of the current
whenever we have a connected
circuit there will be a current
and whenever we have a current there will be magnetic field
what causes the current?
flow of electrons
So what causes the production of magnetic
field around any wire having current?
Electrons are the particles within an atom that are resposible for the production of magnetic field
So by placing a ferromagnetic material inside a solenoid
the strength of the magnetic field increases
Why???
As you know a temporary magnet can be made by
either
or
Rubbing the material
with one pole of a magnet
Placing unmagnetized ferromagnetic material in a strong magnetic field
What are the metals that can be attracted by a magnet?
iron, nickel and cobalt
Such materials show strong magnetic properties where they
can be changed into extremely strong magnets.These materials
are called "Ferromagnetic materials"
How can we change such
materials to strong magnets?
In case of solenoid where does the
strong magnetic field exist?

Inside the solenoid
in its center

Because the ferromagnetic material is going to
become a magnet in the solenoid's magnetic field
What is an
electromagnet?
solenoid
+
ferromagnetic core
Electromagnets have
two sources of magnetic field
Magnetic field
due to the
current in
the wire
Magnetic field
due to the
magnetized core
(Temporary magnet)
Overall magnetic = magnetic field due + magnetic field due
field to current to magnetized core
This overall magnetic field can be hundreds or thousands of times stronger than the magnetic field produced by the current alone
Strong magnet
that can be
turned on or off
or
The strength of electromagnet can be increased
by increasing the strength of the magnetic field

How can we strengthen
such field???
Increase the
current in the
solenoid

of wire to the
solenoid

Wind the coils closer
together in a
solenoid

Use stronger
Ferromagnetic
material
for the core of the
solenoid
(1)
(2)
(3)
(4)
When the device is "on" it attracts
When the device is "off" it drops
Electromagnets are probably used every day ex: it is used for
recording informations onto audiotapes, videotapes and credit
cards also it is used in doorbells.
How a doorbell works?
Pressing the button
closes the circuit
Closing the circuit turns
on the electromagnet
The electromagnet
attracts the metal bar
The clapper which is attached to the metal bar strikes the bell where the circuit will open turning off the electromagnet
The spring returns the metal bar to its resting position again
Electromagnets are used to lift heavy objects
to lift metal objects a switch is turned on in the
crane, so that a current is produced in the
electromagnet so that there will be attraction

When metal objects need to be dropped, the switch is turned off and the objects fall from the magnet
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