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Chapter 8 Physical Science Notes: Magnetism and Its Uses
Section 1: Magnetism
Vocabulary Terms: 1. Magnetic poles 2. magnetic domains
I. Magnetism
A. Magnetism = refers to the properties and interaction of magnets.
1. Magnetic Force = magnets exert either an attractive or repulsive force
on each other. Strength increases or decreases as distances increase or
decrease.
2. Magnetic fields surround magnets and exert magnetic force.
3. Magnetic poles are regions where the magnetic forces is strongest.
a. Usually referred to as north or south.
i. North always attracts south (vice versa)
ii. north and south poles of magnets cannot be isolated.
4. Earth’s magnetic field is changing about 1 degree per decade. There is
a difference between true north/south versus magnetic north/south.
a. Caused by the Earth’s core, a solid ball of iron and nickel
surrounded by a molten (liquid) layer.
B. Magnetic Materials
1. Not all metals are magnetic. Try sticking a magnet to a pop can!
2. Electrons of the elements cause magnetic properties. The affect of
electrons often cancel each other out creating a nonmagnetic element
3. Elements such as iron, cobalt, and nickel make great permanent
magnets due to their electron configuration.
4. Magnetic domains = groups of atoms with aligned magnetic poles.
a. Magnetic domains can be induced (forced to align) by applied
magnetic fields. This is why a nail, which is normally
nonmagnetic becomes magnetic when touched to a magnet or
electrical current.
Section 2: Electricity and Magnetism
Vocabulary Terms: 3. electromagnet 4. galvanometers 5. electric motors
II. Electricity and Magnetism
A. Electric Current and Magnetism
1. In 1820 a Danish physics teacher (Hans Oversted) accidentally noticed
that electric current caused a compass needle to align or deflect.
2. Moving charges (current) produces magnetic fields.
3. The strength of magnetic field depends on the amount of current.
B. Electromagnets = a temporary magnet made by placing a piece of iron inside a
coil of wire.
1. Properties of Electromagnets
a. Converts electric energy into mechanical to do work.
b. Amount of magnetism controlled by the amount of current
c. Used in speakers to vibrate parts of the speaker to produce
sound.
C. Galvanometers = devices that use an electromagnet to measure electric
current.
1. Used in many automotive gauges like temperature and fuel.
D. Electric motors = converts electrical energy into mechanical
1. First developed in 1873
2. Too many uses to list!!!
Section 3: Producing Electric Current
Vocabulary Terms: 6. electromagnetic induction 7. generator 8. turbines 9.
alternating current (AC) 10. direct current (DC) 11. transformer
III. Producing Electric Current
A. From Mechanical to Electrical
1. Electrical Induction = producing an electric current by moving a loop
of wire through a magnetic field or vice versa.
2. Generators produce electricity by rotating a coil of wire in a magnetic
field.
a. Examples
1. alternators
2. Wind generators
3. Utility Electric Generator
B. Types of Current
1. Alternating Current (AC) = reverses the direction of current
flow in a regular way.
a. U.S. uses 60 Hertz frequency AC so that means it
changes direction 120 times per second.
b Europe uses 50 Herts frequency AC, so it changes
direction 100 times per second.
c. Appliances are usually marked 60 Hz or 50/60 Hz if it is
ok to use it in the US and Europe.
2. Direct Current (DC) = flows in only one direction through a
wire.
a. Batteries produce direct current.
C. Transformers = increases or decreases the voltage of alternating
current.
1. Transformers boost voltage to transport as much current over
long distances. See high voltage power lines in the countryside.
Referred to as stepping up. This maximizes current while keeping
resistance from wires constant.
2. Transformers also step down once the current gets to its
destination.