Magnetism

• Similar to electric forces• Magnetic Poles • North and South Poles• Historic Designations• Like Poles Repel, Unlike Poles Attract• Due to alignment of atoms in material

Magnetic Fields

• Similar to electric and gravitational fields• Magnetic fields are produced by the

MOTION of electric charges

Magnetic Fields

• Revolving electron produces field• Spinning electron produces field• In most atoms, combination of spins and

orbits are in opposite directions• The fields cancel each other out• Some atoms, they don’t cancel• Iron, nickel, cobalt, aluminum

Magnetic Domains

• In iron, for example, field by an atom is so strong it causes neighboring atoms to arrange their spins and orbits to line up

• These clusters form magnetic domains• Domains are randomly oriented in ordinary

iron, nickel, etc.• Can force them to line up with external

field

Electric Currents & Magnetism

• A moving charge produces a magnetic field

Electric Currents & Magnetism

Electromagnetics

• Place a piece of unmagnetized iron in a coil of wire carrying a current

• Produce a strong magnetic field in the iron by lining up domains

• Makes the whole thing a very powerful magnet

Magnetic Forces and Charges

• If a charge isn’t moving, a magnetic field has no effect on the charge

• Reciprocal kind of idea• Moving charges produce magnetic fields• Magnetic fields apply a force to a moving

charge

Magnetic Forces and Charges

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Magnetic Forces and Charges

Magnetic Forces and Charges

Meters

• Use a compass needle (magnet)

Meters

Motors

Electromagnetic Induction

Electromagnetic Induction

Electromagnetic Induction

Electromagnetic Induction

Electromagnetic Induction

• Faraday’s Law• The induced voltage in a coil is

proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loops.

• The amount of current depends on the resistance of the wire

• Changing magnetic field in a loop is key!!

Electromagnetic Induction

• Traffic light control (buried loops)• Airport Security Systems• Mag strips on credit cards• Tape Recorders• Computer Hard Drives

Generators

Generators

Power Production

Transformers

Transformers

• The more turns, the more voltage induced• Step-up Transformer has more turns in

secondary than in primary• Step-down Transformer has more turns in

primary than in secondar

Transformers

• Energy Conservation• Power In = Power Out

Vin Iin Vout Iout

Field Induction

• An electric field is induced in any region of space in which a magnetic field is changing with time

• A magnetic field is induced in any region of space in which an electric field is changing with time

• “Let there be light!!!”