Chapter 20 Magnetic Fields
20.1 Concept of a Magnetic Field
Magnetic Field
A region of space in which a magnetic pole experiences a force.
Law of Magnets
Like poles repel, unlike poles attract.
Producing a Magnetic Field
A magnetic field can be created by:
1) Permanent Magnets 2) Movement of Electric Charges (in a wire)
• Materials that produce a magnetic field. • A stationary charge will not produce a
magnetic field.
• A magnetic field is created around a current
carrying wire due to the movement of
electrons.
All magnetic fields are created by moving charges.
In a permanent magnet: In a wire:
▪ The magnetic field is produced by the ▪ The magnetic field is produced by the
movement of electrons within the atom of movement of free electron in the wire.
the magnet.
▪ Each electron represents a tiny current as it
circulates around within its atom.
▪ The current produces a magnetic field.
, Representing Magnetic Fields
Magnetic field patterns are represented by magnetic field lines.
Key Aspects of Magnetic Field Lines:
1) The magnetic field lines come out of North poles and go into South poles.
2) The direction of a field line at any point in the field shows the direction of the force a ‘free’
magnetic north pole would experience at that point.
3) The strength of the magnetic field is indicated by the closeness of the lines.
▪ The closer the lines are together, the stronger the magnetic field.
▪ The further apart the lines are, the weaker the magnetic field.
4) The magnetic field lines are continuous smooth curves which never touch or cross.
5)
Magnetic field out of the page Magnetic field into the page
Magnetic Field Patterns
1) A single bar magnet 2) Two attracting bar magnets
3) Two repelling bar magnets
• X is known as a neutral point.
• Where there is no resultant magnetic field because
the two fields are equal in magnitude but opposite
in direction.
20.1 Concept of a Magnetic Field
Magnetic Field
A region of space in which a magnetic pole experiences a force.
Law of Magnets
Like poles repel, unlike poles attract.
Producing a Magnetic Field
A magnetic field can be created by:
1) Permanent Magnets 2) Movement of Electric Charges (in a wire)
• Materials that produce a magnetic field. • A stationary charge will not produce a
magnetic field.
• A magnetic field is created around a current
carrying wire due to the movement of
electrons.
All magnetic fields are created by moving charges.
In a permanent magnet: In a wire:
▪ The magnetic field is produced by the ▪ The magnetic field is produced by the
movement of electrons within the atom of movement of free electron in the wire.
the magnet.
▪ Each electron represents a tiny current as it
circulates around within its atom.
▪ The current produces a magnetic field.
, Representing Magnetic Fields
Magnetic field patterns are represented by magnetic field lines.
Key Aspects of Magnetic Field Lines:
1) The magnetic field lines come out of North poles and go into South poles.
2) The direction of a field line at any point in the field shows the direction of the force a ‘free’
magnetic north pole would experience at that point.
3) The strength of the magnetic field is indicated by the closeness of the lines.
▪ The closer the lines are together, the stronger the magnetic field.
▪ The further apart the lines are, the weaker the magnetic field.
4) The magnetic field lines are continuous smooth curves which never touch or cross.
5)
Magnetic field out of the page Magnetic field into the page
Magnetic Field Patterns
1) A single bar magnet 2) Two attracting bar magnets
3) Two repelling bar magnets
• X is known as a neutral point.
• Where there is no resultant magnetic field because
the two fields are equal in magnitude but opposite
in direction.
