Magnetic Fields

• Magnetism: a force that exists between moving charges.

• Magnetism is created naturally by the spinning of electrons in atoms.

• Where there is electricity there is always magnetism!

• Magnetic field: the space around a magnet in which magnetic forces can be detected. Unit is the tesla.

• Magnetic flux lines: imaginary lines indicating the magnitude and direction of a magnetic field. The Weber is the unit for measuring the number of lines of flux.

• Magnetic domain: region in which the magnetic fields of atoms are grouped together and aligned.

Properties

• The magnetic field lines come out of the magnet at its north-pole and enter the magnet at its south-pole.

• The direction of the magnetic field lines is the direction to which the north-pole of a compass points when it is placed in the magnetic field.

• Opposite poles attract, like poles repel each other.

• Magnetic field lines always form closed loops.

• The magnetic field lines continue through the inside of the magnet.

Earth as a Magnet

• The Earth acts asThe Earth acts as• a giant magnet.a giant magnet.

• The magnetic south pole can The magnetic south pole can be found near the geographic be found near the geographic north pole and vice versa.north pole and vice versa.

• The magnetic poles move over The magnetic poles move over time.time.

• The Earth’s poles actually The Earth’s poles actually reverse about every 250,000 reverse about every 250,000 years on average. They last years on average. They last reversed about 780,000 years reversed about 780,000 years ago.ago.

Movement of the South magnetic pole in the Northern hemisphere.

Applications

• Navigation: animals, compasses

• MRI’s

• Particle Accelerators

• Maglev trains

• Aurora Borealis

• Electrical transformers

• Sticking notes to your refrigerator

• Creating electrical currents

• Audio cassettes, VHS

• Credit/Debit cards

• Health benefits?

Electromagnetism

• Solenoid: a coil of wire wrapped around a conducting rod. When a current is sent through the wire, a magnetic field is created inside the rod.

• The magnetic field strength can be increased by increasing the current, increasing the number of loops, or increasing the permeability (the degree of magnetization of a material in response to a magnetic field).

Transformers

• As electricity flows through the wire, resistance decreases the voltage. There are also times that we want to decrease the voltage to bring it down to useable levels.

• Transformers allow us to do this.

• They are made out of two solenoids with varying amounts of loops.

• Step up transformers have fewer coils of wire in their primary coil than in their secondary coil and voltage is increased.

• Step down transformers have more coils of wire in their primary coil than in their secondary coil and voltage is decreased.