CHPT 2 NOTES
MAGNETISM
I. Magnetism makes our planet able to support life:
A. Earth has a magnetic field similar to the field around a bar magnet.
1. Current theory says it is caused by the Earth's iron core.
2. Earth's magnetic field has reversed in the past.
3. Earth's magnetic North pole is not located exactly on the geographic North pole. (The geographic North pole is the point at which the Earth rotates on its axis.)
B. Van Allen Belts -- areas of magnetic force lines around the Earth where charged particles from the sun have been trapped.
1. solar wind -- charged solar particles (form of radiation)
2. Life is possible here because we don't get hit with intense radiation.
C. Astrobiology - the study of life in other parts of the universe
II. Magnets - All magnets have N and S poles.
A. What we have learned about behavior of magnets:
1. When free to move, magnets line up along the Earth's magnetic force lines, N & S
2. Strong magnets can sometimes magnetize other metals.
3. RULE: Like poles repel / Opposite poles attract
4. Not all metals are magnetic
5. Magnetic force still works through paper & other materials
6. Magnetic fields have patterns
(See pg 53, 55 & 56 for illustrations)
7. Magnetic force is strongest at the poles
8. When you break a magnet, you get 2 whole new magnets (N-S & N-S)
B. History -- Lodestone -the old name for naturally magnetic rocks
1. discovered by the Greeks
2. now called iron oxide(Fe2O3)
C. Compass -- a tiny magnetic pointer floating freely in a liquid
1. Usually lines up N & S with the magnetic force lines of the Earth
(See diagram on pg 52)
2. If a compass is near a strong magnet, the pointer will line up with that magnet's magnetic force lines.
(see diagram on pg 52 - 53)
III. Magnetic Domain Theory -- Magnetism is caused by tiny magnetic regions all lining up the same way on the molecular level.
>>>>>>>>>>>>> <><^>><<^><
>>>>>>>>>>>>> v^v<><^V>^^<
magnetized iron unmagnetized iron
(domains are aligned) (domains are mixed up)
IV. Induced Magnetism -- When an unmagnetized object is brought near a strong magnetic field, its domains will all line up and it will become a magnet
A. ALNICO -- an alloy made of Aluminum, Nickel and Cobalt that makes good
permanent magnets.
B. Electromagnets -- A current-carrying wire creates a N & S pole. Its magnetism can be turned off.
1. more coils = more magnetism
2. more volts = more magnetism
3. iron core = more magnetism
V. Loudspeakers use an electric coil and a permanent magnet to vibrate a paper cone. This produces sound. When electricity changes direction, it reverses
the N & S of its electromagnetic field. (Then it pushes and pulls the paper cone, producing sound.)
VI. Electric Motor -- device that changes electrical Energy to motion (mechanical E)
1. rotating coil is called an armature
2. commutator changes direction of current
VII. Transformer -- device that increases or decreases voltage
A. Step up -- when small # of coils lead to large # of coils, this increases voltage (Ex: neon sign)
120 V 240 V
in-----> ----> output
Primary coils (100 wraps) Secondary coils (200 wraps)
B. Step down -- when large # of coils lead to small #of coils, this decreases
voltage (Ex: toy trains)
120 V 6 V
input ---� output
Primary coils Secondary coils
(100 wraps) (5 wraps)
VIII. Electric Generator -- a device that uses a magnet to change mechanical energy to electric Energy.
A. Electric currents can be measured by these devices:
1. ammeter measures amps
2. galvanometer measures small amp levels
3. voltmeter measures volts
B. When a coil moves through a magnetic field an induced electric current is produced
