Magnetism

• Magnetism is a force caused by moving charges

• Magnets are dipoles (they have a north and a south)

• Like poles repel, opposite poles attract

• Magnetic domains are clusters of atoms with electrons spinning in the same direction

  • Random domains: no net magnetic field

  • When many of the domains line up, you get a net magnetic field, creating a strong magnet

  

Magnetic Fields

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  • Units a Tesla (T)

• Magnets are polarized (each has two opposite ends)

  • End of a magnet that points toward the geographic north pole of the Earth is called the north pole of the magnet

  • There are no magnetic monopoles

Magnetic Field Lines

• Magnetic Field Lines make closed loops and run from north to south outside the magnet

  • Magnet field lines show the direction the north pole of a magnet would tend to point if placed in the field

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The Compass

• The Earth is a giant magnet

• The Earth's magnetic north pole is located near the geographic south pole, and vice versa

  • A compass's north magnet pole points toward the Earth's magnetic south pole (geographic north)

• A compass lines up with the net magnetic field

  

Magnetic Permeability

• Magnetic permeability refers to the ratio of magnetic field strength induced in a material to the magnetic field strength of the induced field

  

• Free space has a constant value of magnetic permeability that appears in physical relationships

  

• The permeability of matter has a value different from that of free space

• Highly magnetic materials (such as iron) have higher values of magnetic permeability

Magnetic Dipole Moment

• The magnetic dipole moment of a magnet refers to the force that a magnet can exert on moving charges

• Can be thought of in simplistic terms as the relative strength of a magnet

  • Compare the magnetic dipole moment of a hydrogen atom to the magnetic dipole moment of a highly magnetized iron bar

  • Fe > H