Make your own free website on Tripod.com
Unit 5 Notes
20-2                The Earth as a Magnet         

The Earth behaves like it has a huge bar magnet in it and it is surrounded by a magnetic field that is strongest near the North and South Poles.

The Earth's magnetic poles reverse each half million years or so - this is recorded in the geologic rock record of the Earth.

The Sun is also a source of magnetism. It's magnetic field reverses itself about every 11 years.

20-3                   Magnetism in Action

The Earth's magnetosphere deflects much of the solar wind because charged particles moving at angles to a magnetic field will tend to spiral around magnetic field lines.  This, in part, accounts for the auroras at the Earth's northern and southern regions.
Physical Science Chapter 21 Electromagnetism
21-1 Magnetism from Electricity

Current passing through a wire creates a magnetic field.

Oersted discovered that an electric current flowing through a wire causes a magnetic field whose direction (where the north and south poles are)  depends on the direction of current.

Solenoid: A long coil of wire that acts as a magnet when a current passes through it.

Electromagnet: A temporary magnet created by passing a current through a coil of wire.  (A solenoid with an iron core.)



A magnetic field will exert a force on a wire carrying a current.
Electric Motor: A device that changes electrical energy into mechanical energy in order to do work.

Galvanometer: An instrument that detects electric current. (p540) It can also detect the direction of current flow.

Ammeter: Contains a galvanometer   
                Measures the current passing through a circuit in amperes.  (Connected in "series")

Voltmeter: Contains a galvanometer Measures the "potential difference" of a circuit in volts.   (Connected in "parallel")

Commutator: A reversing switch on a generator that rotates with the electromagnet - changing the direction of the current.

21-2      Electricity from Magnetism

Electromagnetic Induction: Moving a wire through a magnetic field produces a current in the wire.

Faraday discovered that a steady magnetic field did not produce an electric current. However, a changing magnetic field did "induce" a current.
(This is called electromagnetic induction.)

Generator:   Produces an electric current by rotating a loop of wire in a magnetic field.

Direct Current ( DC ): Electrons flow only in one direction through a wire - "negative" terminal to "positive."


Alternating Current ( AC ):   Electron flow  reverses direction in a regular pattern. In the United States, household current is AC with electron flow reversing 60 times a second.
(60 cycles per second or 60 Hertz (Hz).)

Transformer:   Increases or decreases the voltage of AC. The process involves both  "electromagnetism" and "electromagnetic induction."