ELECTROMAGNETISM

The marriage of electricity and magnetism

ELECTROMAGNETISM

Different aspects of the same force:Electromagnetic Force

Four fundamental forces of nature• Gravity• Nuclear• Nuclear Interaction• Electromagnetism

HISTORY

• Luigi Galvani = Frog leg

• Alessandro Volta = Voltaic pile (Battery sandwich)

• Stacked copper and zinc together with a layer of wet paper between metals producing a weak current

Invention of the battery led to the understanding of electromagnetism and their symbiotic relationship• Modern batteries• Positive carbon

rod• Surrounded by

electrolytic paste• Housed in a

negative zinc.

Invention of the battery led to the understanding of electromagnetism and their symbiotic relationship• Therefore a

battery is a source of conversion of some form of energy (magnetic) into electric current

• Battery is a source of EMF

Hans Oersted

• Discovered the relationship between magnetism and electric current

• A magnetic field is produced by current running through the wire

“Hand” Rules

• Right Hand rule• Thumb indicates

the direction of the current

• Fingers indicate direction of magnetic field lines

• Fleming’s Right Hand Rule

• Determines the pole of the solenoid

• Thumb points to the north pole, Fingers represent the direction of the current

• Flemings right hand generator rule:

• Thumb is the direction that the conductor is moving

• Index point to the direction of magnetic lines

• Middle finger=current flow

“Hand” Generator rules

• Flemings left hand generator rule:

• Thumb is the direction that the conductor is moving

• Index point to the direction of magnetic lines

• Middle finger=electron flow

Faraday Rule

• AKA: 1st law of Electromagnetism• A magnetic field cannot be still and

produce a current. But if the magnet is moving a current is produced.

Furthermore: Induced current by a magnet depends on • Strength of magnetic field• Velocity of magnetic field• Angle of the conductor to the

Magnetic field• # of turns in a conductor

• Answers: 99-B• 100 - C

TO PRODUCE electric current• Move a bar near a coil of wire• OR• Move coil of wire near stationary

magnet• Current increases with increase in

magnetic field

LENZ’S LAW

• Most important thing to remember even if you do not understand this law is the following:

• It is the basis for self induction• The autotransformer and choke

coil in an x-ray circuit both run on self induction

HERE WE GO

Lenz’s Law: Induced current flows in a direction such that it opposes the action that induces it

Lenz’s Law answers this question• Which end of the coil that has had

current induced will be the north or south pole?

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