Magnetism

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Magnetism
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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.
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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
  attract.

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Magnetic Poles

• Northseeking 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.

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Domain Theory

• All magnetism is due to the motion of electrons.
• Electrons spin, like the earth, setting up
  magnetic poles. (paramagnetism)
• Electrons revolve around the nucleus, like the
  earth around the sun. (diamagnetism)
• Electrons are paired in orbitals. Paired
  electrons spin opposite directions- creating
  opposite magnets. The magnetic poles therefore
  cancel each other. Unpaired electrons create
  stronger magnets. (ferromagnetism)

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• Magnetic domains- clusters of aligned atoms

Magnetic Saturation all the domains are
aligned Dropping a magnet can cause the domains
to become unaligned.
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Select your answer a or b and explain why.
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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?
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• Concept check 1
• Must every magnet have a north and south pole?
  Explain.
• How can a magnet attract a piece of iron that is
  not magnetized?
• Why will a magnet not pick up a penny or a piece
  of wood?
• If you break a magnet have you destroyed it?

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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 _______.

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• A moving electron has a ___________ field and an
  ___________field around it.
• Magnetic field lines show the ________ and the
  __________ of the field.
• A magnetic field goes from _____ to ____.
• Paramagnetism is due to _________.
  Diamagnetism is due to ____________.
• Ferromagnetism is due to _____________.

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Magnetism and Current

• What causes all magnetism?
• What is current?
• Will current cause magnetism?

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Electromagnets
Materials list
wire
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.

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Faradays Law
The induced voltage in a coil is proportional to
the number of loops multiplied by the rate at
which the magnetic field changes within those
loops.
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Lenzs Law
The current induced in a wire is such as to
oppose the force that induced it.
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Generator
Mechanical energy electrical energy
Motor
Electrical energy Mechanical
energy
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Domain Theory Paramagnetism- weak attraction
due to spin of electrons Diamagnetism weak
repulsion- due to revolving electrons Ferromagnet
ism strong-due to unpaired electrons
Magnetism vs. electricity Both due to
electrons Both force at a distance Both like
repel unlike attract BUT magnetic poles cannot
be separated
Magnetism