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Transcript Magnetism

Magnetic field –
Region where a
magnetic influence
(force) can be felt.
Lines are drawn to
represent the strength
and direction of the
field. Field is
represented from N to S.
Magnetic Forces
• Magnetic forces, like electrical forces, are
forces that act at a distance. (Objects do not
have to be in contact.)
• Like poles repel each other; opposite poles
Magnetic Poles
• North–seeking poles- point northward.
• South-seeking poles – point southward.
Important difference between electric charges
and magnetic poles is that electric charges
can be isolated, but magnetic poles cannot.
Domain Theory
• All magnetism is due to the motion of
• Electrons spin, like the earth, setting up
magnetic poles. (paramagnetism)
• Electrons revolve around the nucleus,
like the earth around the sun.
• Electrons are paired in orbitals. Paired
electrons spin opposite directionscreating opposite magnets. The
magnetic poles therefore cancel each
other. Unpaired electrons create
stronger magnets. (ferromagnetism)
• Magnetic domainsclusters of aligned
Magnetic Saturation –
all the domains are
Dropping a magnet can
cause the domains to
become unaligned.
Select your
answer a or b and
explain why.
DO NOT COPY the questions.
Answer each with an illustration (drawing.)
1. What is the advantage of using a horseshoe
magnet over a bar magnet –assuming the two
are identical as bar magnets?
2. You are required to build a model of the
Earth and its magnetic field using a ball of
clay and a bar magnet. You will be forming
the clay Earth around the magnet. What is the
orientation (direction) of the magnet?
Concept check 1:
1. Must every magnet have a north and south pole? Explain.
2. How can a magnet attract a piece of iron that is not
3. Why will a magnet not pick up a penny or a piece of wood?
4. If you break a magnet have you destroyed it?
1. An iron nail is strongly attracted to the north end, the south
end or both ends of a magnet equally strong.
2. Magnetism is due to the motion of the electron as they
__________ and ______________.
3. Several nails dangle from the north pole of a magnet. The
induced pole on the top of the first nail is______. The
induced pole on the bottom of the lowestmost nail is
4. A moving electron has a ___________ field and
an ___________field around it.
5. Magnetic field lines show the ________ and the
__________ of the field.
6. A magnetic field goes from _____ to ____.
7. Paramagnetism is due to _________.
Diamagnetism is due to ____________.
Ferromagnetism is due to _____________.
Magnetism and Current
• What causes all magnetism?
• What is current?
• Will current cause magnetism?
Materials list:
power supply (current)
core (anything from air to metal)
The strength of an electromagnet can be
increased by
•increasing the current in the wire,
•increasing the number of turns of wire, or
•by using a metal core.
Lenz’s Law
The current induced in a wire
is such as to oppose the force
that induced it.
Mechanical energy
electrical energy
Electrical energy
Mechanical energy
Magnetism vs. electricity
Both due to electrons
Both force at a distance
Both like repel unlike attract
BUT magnetic poles cannot
be separated
Domain Theory
Paramagnetism- weak attraction –
due to spin of electrons
Diamagnetism – weak repulsiondue to revolving electrons
Ferromagnetism – strong-due to
unpaired electrons