Magnetism Magnetism is the force of attraction or repulsion

of a magnetic material due to the arrangement of its atoms, particularly its electrons.

Like poles will repel, opposite poles will attract.

Magnetic field lines describe the structure of magnetic fields in three dimensions.

At the poles of a magnet, the magnetic field lines are closer together.

The strength of the magnetic field is greater where the lines are closer together and weaker where they are farther apart.

Magnetic Domains Moving electrons produce magnetic fields.

In most materials, these magnetic fields cancel one another and neutralize the overall magnetic effect.

In other materials, such as iron, cobalt, and nickel, the atoms behave as tiny magnets because of certain orientations of the electrons inside the atom.

These atoms are grouped in a tiny region called the magnetic domain.

The Earth is a Magnet It exerts a magnetic forces and is surrounded by a magnetic field that

is strongest near the North and South magnetic poles. The Earth’s magnetosphere extends far out into space and is

constantly bombarded by magnetic particles from the sun – “solar wind”.

How to remove magnetism Drop the magnet Heat the magnet

The Curie point is the temperature at which the magnetic properties of a substance are removed and is different for each substance.

Magnetic Fields Produced by Conductors

And how to switch on and off the strangely attractiveness

Effects of Domain Theory

• Magnetic Induction• Demagnetization• Reverse Magnetization• Breaking a Bar Magnet• Magnetic Saturation• Induced Magnetism by Earth• Keepers for Bar Magnets

Oersted’s DiscoveryIn 1819, the Danish physicist

Hans Christian Oersted (1777-1851) discovered the connection between electricity and magnetism by accident while lecturing at the University of Copenhagen. He noticed that a compass needle placed closely to a current carrying wire would take up a position nearly perpendicular to the direction of the current.

Principle of Electromagnetism

Whenever an electric current moves through

a conductor, a magnetic field is created in the

region around the conductor.

Magnetic Field of a Straight Conductor The magnetic field lines for a straight

conductor are concentric circles around the conductor.

• If a straight conductor is held in the right hand with the right thumb pointing in the direction of the electric current, the curled fingers will point in the direction of the magnetic field lines.

The Right-Hand Rule

Parallel Wires

How is the scrap metal held up by the crane?

Electromagnets A device that exerts a magnetic force using

electricity. The magnetic field around a straight

conductor can be intensified by bending the wire into a loop.

Coil or Solenoid The magnetic field can be further intensified

by combining the effects of a large number of loops would close together to form a coil, or solenoid.

• If a coil is grasped in the right hand with the curled fingers representing the direction of electric current, the thumb points in the direction of the magnetic field inside the coil.

The Right-Hand Rule

Parallel Coils

Factors Affecting the Magnetic Field of a Coil

Current in the Coil• The more

current, the greater the concentration of magnetic field lines in the core.

Number of Loops• The more

loops, the stronger the magnetic field since the magnetic field is the sum of the field of each loop.

Type of Core Material• The core of a

coil can greatly affect the coil’s magnetic field strength.

• A core of iron will increase the strength compared to that of air.

Type of Core Material The core material becomes an induced

magnet, as its atomic dipoles align with the magnetic field of the coil. The core itself becomes an induced magnet.

The factor by which a core material increases the magnetic field strength is called the material’s relative magnetic permeability (K).

• Materials that become strong induced magnets when placed in a coil.

• Iron, nickel, cobalt, and their alloys.

Ferromagnetism

• Materials that magnetize slightly when placed in a coil and increase the field strength by a barely measurable amount.

• Oxygen and aluminum.

Paramagnetism

• Materials that cause a very slight decrease in the magnetic field of a coil.

• Copper, silver, and water.

Diamagnetism

Applications of Electromagnetism