Download the magnetic field the electric field

In the first part we are going
to show :
• The magnetic phenomena
• The magnetic poles
• Field lines
• The differences between the
magnetic and the electric field
THE MAGNETIC
PHENOMENA
We know that in nature there are some
‘ferromagnetic materials’ which can be
magnetized.
For example, the magnetite attracts iron: if we
accost a bar of iron to the magnetite, it
becomes a magnet.
THE MAGNETIC POLES
Each magnet has two poles : the north and the south.
Similar magnetic poles repel each other, different ones attract.
In fact,in the magnetic field of the Earth the geographic South and
the North pole don’t match with the magnetic ones.
THE FIELD LINES
Field lines are generated by two poles characterized of direction and verse :
• Direction is given by the straight line that links the two poles.
• Verse goes from the North to the South Pole .
So the field lines:
• are bribes to the direction of the field.
• get out from the North Pole of the magnets and goes to the South.
• their density is directly proportional to the intensity of the field.
DIFFERENCES BETWEEN MAGNETIC
AND ELETRIC FIELDS
THE MAGNETIC FIELD
THE ELECTRIC FIELD
Because of the magnetization of Instead, in this case, the charges
a ferromagnetic object, there
go from the first to the second
aren’t passages of magnetic
corp.
poles.
The two poles can’t divide.
There are isolated positive or
negative electric charges .
In the second part we are going to
show:
• The magnetic field generated by a wire
crossed by current
• The experiences of some of the most important
scientists
• The flow in a flat surface
MAGNETIC FIELD GENERATED BY A
WIRE CROSSED BY CURRENT
What did Oersted find out?
The experience of Oersted shows that a wire
crossed by current generate a magnetic field.
What did Faraday find out?
Instead,thanks to Faraday,we know that
this wire crossed by current,in a magnetic field, is subjected to a
force.
The verse of the magnetic force is given by
the right hand rule.
Thanks to Oersted and Faraday we
know that
There’s a relation between electric current and
the magnetic field because the electric current:
• Generates a magnetic field
• Is subjected to a magnetic force.
So it is possible that there would be a magnetic
force between two wires because each of them
has those characteristics.
AMPERE
He experienced that :
• two straight and parallel wires attract each other
if they are crossed by a current in the same verse
and they repulse if it is opposite.
• Between this two wires there’s a magnetic force.
The Ampere’s law
The force of a wire is directly proportional
to the two currents that are circulating
but it also indirectly proportional to the
distance between the wires.
What is an ampere?
It’s a fondamental unite of measure of SI.
It’s the intensity of electric current in two straight
and parallel conductors situated 1 metre to the
other in the vacuum. There’s a force of 2x10^7
N.
The amperometer is used to measure the intensity
of the current and it’s inserted in a circuit where
there’s the current we want to measure.
What is a coloumb?
It’s the charge that goes throught a section of the
wire in which there’s the electric charge of 1
ampere.
THE INTENSITY OF THE
MAGNETIC FIELD
As regards the direction and the verse,we use a
magnetic needle. For the intensity we use a wire
crossed by current in the magnetic field.
B=F/il
THE MAGNETIC FORCE ON A WIRE
CROSSED BY CURRENT
Once you’ve known the magnetic field,you can calculate this force.
When the wire is perpendicular to the field lines,it is subjected to a force
F=Bil
It is perpendicular to the magnetic field and the wire. Instead the verse is given
by the right hand rule.
• When B is perpendicular the magnetic force is maximum.
• When B is inclined, B is lower.
• When B is parallel to the wire,the magnetic force is zero.
THE MAGNETIC FIELD GENERATED BY
A WIRE CROSSED BY CURRENT
The force that the second wire gives to the first one is equal and
opposite. So,two equally orientated wires attract each other. In
the other case,the wires repulse.
THE MAGNETIC FIELD OF A SPIRE
Let’s consider a spire ( a
circular conductor wire)
crossed by current ; in
every point, B is
perpendicular.
The verse is given by the
right hand rule.
The intensity by :
B= (µ/2) (i/R)
THE MAGNETIC FIELD OF A SOLENOID
The solenoid is made up of a wire
which is wrapped to a propeller.
If it is infinitely wide:
The outer magnetic field is equal to
zero, instead the interior one is
uniform and parallel.
If it is normal:
The interior magnetic field is
particularly intense,instead the outer
one is weak.
In the middle the lines are parallel
and equidistant,that’s why the
magnetic field is uniform.
B=m(Ni/l)
Aurora borealis
This is a phenomena that occurs near the magnetic poles.
It’s the result of collisions between gaseus particles in
Earth’s atmosphere with charged particles released
from the sun’s atmosphere. The colour is given by the
type of gas that are colliding.
LORENTZ’S FORCE
•Magnetic field is produced
by electric charges which are
in motion.
•These electric charges are
subjected to strength due to a
magnetic field.
Magnetic force works on a moving charge.
THE MOTION OF A CHARGE IN A
AN UNIFORM MAGNETIC FIELD
DK=W=0
(Because of the cinetic energy theory)
So the cinetic energy of the charge
doesn’t change.
The Lorentz’s force can’t change the
value of the charge’s velocity.
Motion with perpendicular velocity
to a uniform field (B)
The Force :
• Is always perpendicular to velocity
• Is perpendicular to B
• Has a constant value given by Fq=qvB
r=mv/qB
The flow in a flat surface
F(B)=BS=Bscosa
The flow is measured in weber.
• It is positive when the lines of the magnetic field come out.
Cosa>0
• It is negative when the lines of the magnetic field come in.
Cosa<0
The flow in a no-flat surface
The surface is divided in n parts.
Gauss’ theorem for magnetism
In every closed surface it is equal to zero.
F(B)=0
Thank you for your
attention.
Team n.6 :
Castelluccio Camilla
Foglio Arianna
Identi Noemi Lina
Marasco Antonio
Russo Carmine