Welcome to Professor MAD.
Physics for Everyone.
Today we are going to talk about Magnetism.
The first thing we know about magnets
is that magnets attract specific metals.
Metals that naturally attract magnets are known as Ferromagnetic Metals.
These Metals will firmly stick to these magnets.
For example,
Iron, Cobalt, Steel, Nickel, Manganese, Gadolinium and lodestone
are all ferromagnetic metals.
When a freely suspended magnet comes to rest,
it always rests in the north-south direction.
So the direction points to the geographic North of the earth
is called the magnet's North Pole.
The direction pointing to the geographic South
is called the magnet's South Pole.
This property is especially useful in navigation.
The magnetic compass is built based on this.
Another interesting property of a magnet is
opposites attract and likes repel.
If you have two bar magnets with their ends marked north and south,
then one magnet's North end will attract the other South end.
On the other hand,
the south end of one magnet will repel the south end of the other.
And also North will repel the North.
Magnetic field is the
region around a magnetic material
within which the force of magnetism acts.
A magnetic field is represented by a series of lines around a magnet.
To have a better view,
let's erase some.
The direction of magnetic field lines is
always from the North Pole to the South Pole.
We show it using arrowheads.
The total magnetic field which passes through a given area
is called the magnetic flux density.
It is denoted using the letter B.
If we consider a bar magnet,
the magnetic field lines around it can be shown like this.
Let's consider area A.
If we place it near the pull end of the magnet,
the number of magnetic fields passing through the area is high.
If we set it somewhere else like this,
the number of magnetic field lines passing through the area is low.
The SI unit of the magnetic flux density is Tesla.
It is a measurement of the magnetic field strength.
In 1820,
Danish natural philosopher Hans Christian Ersted noticed that,
when he turned on an electric current by
connecting the wire to both ends of the battery,
a nearby compass needle deflected away from magnetic north
where it normally pointed.
He discovered that,
a current carrying conductor produces a magnetic field around it
This suggested a relationship between
the moving electric charge and the magnetic field.
This phenomenon is called Electromagnetism.
This is a current carrying conductor wire.
The magnetic field lines around the long wire,
which carries an electric current
form concentric circles around the wire.
The direction of the magnetic field is perpendicular to the wire.
There is a simple method
to find out the direction of
the magnetic field around a wire.
Take your right hand
and point the thumb in the direction of the current.
The direction of your other fingers curling
is the direction of the magnetic field.
This is a current carrying wire.
We can find the magnetic field using the mentioned right hand screw rule.
A single straight conductor wire only creates a very weak magnetic field.
If we wound this conductor into a coil,
we can get more concentrated magnetic field lines.
So in most cases,
Electromagnets are created in this way,
to strengthen the magnetic field.
We can draw the magnetic field around a coil like this.
It's almost like the magnetic field of a bar magnet.
Electromagnets also have magnetic poles.
The direction of the magnetic field
in an electromagnet depends on the direction of the current
There is a simple method to identify the two poles of an electromagnet.
If the electricity travels clockwise around the electromagnet,
then the end you're looking at is the South Pole.
If the electricity travels counterclockwise around the electromagnet,
then the end you're looking at is a North Pole.
In electromagnetism the magnetic field is caused due to the motion of charges.
Not by the conductor itself.
If somehow we move the same number of charged particles without a conductor,
we can still observe the magnetic field.
Actually the moving charges create a magnetic field.
That's all for the introduction of Magnetism.
Watch our next video to learn more about Magnetism.
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