Download Magnetic Fields Produced by a Conductors

Magnetism
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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
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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 Discovery
In 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.
The RightHand Rule
• 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.
Parallel Wires
How is the scrap metal held up by the
crane?
Electromagnets
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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.
The RightHand Rule
• 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.
Parallel Coils
Factors Affecting the
Magnetic Field of a Coil
Current in the
Coil
Number of
Loops
• The more current, • The more loops,
the greater the
the stronger the
concentration of
magnetic field
magnetic field lines
since the magnetic
in the core.
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
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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).
Ferromagnetism
• Materials that become strong induced magnets when
placed in a coil.
• Iron, nickel, cobalt, and their alloys.
Paramagnetism
• Materials that magnetize slightly when placed in a coil and
increase the field strength by a barely measurable amount.
• Oxygen and aluminum.
Diamagnetism
• Materials that cause a very slight decrease in the magnetic
field of a coil.
• Copper, silver, and water.
Applications of Electromagnetism