Transcript Magnetism and Electricity

Magnetism
What is magnetism?
Magnetism is an invisible force seen
when all the electrons spin in the same
direction.
When you bring two magnets together
they exert a push or pull called a
magnetic force.
This force results from spinning electric
charges of electrons in the magnet.
The force can either push magnets
apart, or pull them together.
Magnetic force is one of only three
forces in nature that can act at a
distance. Gravitational and electrical
forces are the other two.
What causes magnetism?
As we saw previously, some
materials are magnetic, some are
not. Why is that?
Well first, remember that all matter
is made up of atoms. These atoms
are made up of 3 smaller building
blocks:
• Protons have a positive charge
• Electrons have a negative charge
• Neutrons have no charge.
Both the proton and neutron are in
the nucleus while the electrons circle
around the nucleus.
What causes magnetism?
As an electron spins, it induces
(makes) a magnetic field.
In magnetic materials, the
electrons move in the same
direction. Electrons do not cancel
out in magnetic materials.
In nonmagnetic materials, like the
magnetic fields of the electrons
cancel each other out. The
electrons are flying around
randomly.
Magnetic Fields
Magnetic field = area around the magnet
where magnetic forces can be detected.
A magnetic object placed in this field will
be affected by the magnet.
The magnetic field is arranged in lines
called magnetic field lines (or flux lines).
Magnetic field lines enter at the south
pole, and exit at the north pole.
Magnetic field lines connect points of
equal magnitude.
Magnetic field lines do not cross each
other.
The magnetic force is strongest where the
lines are most concentrated (near the
poles).
The further from the poles, the weaker the
magnetic field.
Iron filings next to a magnet
Magnetic Poles
Every magnet has a north pole and a
south pole.
If you place the north poles of two
magnets together they will repel or
push apart.
If you place the north pole of one
magnet facing the south pole of the
other magnet, they will attract.
Law of Magnetic Poles = like poles repel
each other, and unlike poles attract each
other.
Magnetic Earth
The Earth is like a giant magnet.
The spinning molten iron and nickel in the
outer core induce a magnetic field called the
magnetosphere.
So if a compass is a tiny magnet, why does the
north end of a compass needle point to the
Earth’s magnetic north if like poles repel?
Look at the Earth’s field lines. They enter at the
magnetic north pole and exit at the magnetic
south pole. How does that compare to what
you learned about field lines?
Don’t field lines on a magnet enter at the
south pole and exit at the north pole?
The north pole of a magnet like a compass gets
its name because it points towards the Earths
geographic north.
The Earth’s magnetic north pole would actually
be a south pole on a magnet.