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Ch 21-Magnetism
Magnetism
• a property of
matter in which
there is a force
of attraction or
repulsion
between like
and unlike poles
Magnetic Poles
• force is strongest at the
magnetic poles: North & South
• Like poles repel, unlike attract
•Force of
attraction
decreases as
distance
between
magnets
increases
If a bar magnet is
suspended so
it turns freely
(like a
compass), it
will point
magnetic N
Permanent Magnets
• made from iron-Fe,cobalt-Co,or nickel-Ni
(aka the IRON TRIAD)
• retain magnetic properties for a long time
Temporary Magnets
• happens when object
is near or is touching
a magnet
• lose magnetic
properties soon after
they are separated
from a magnet
Magnetic field
• area
around the
magnet
where
forces act
Magnetic domains
• groups of
atoms w/
aligned
magnetic
poles
• magnets can
lose some
magnetic
properties if
dropped or
heated “drop it
like it’s hot”
•if a
magnets
breaks, you
have lots of
little
magnets
Star questions
• What is a force of attraction or repulsion between like and
unlike poles?
– Magnetism
• Where is this force the strongest?
– The poles
• What is the Iron Triad?
– Iron, Cobalt, Nickel; only elements to form permanent magnets
• What are groups of atoms with aligned magnetic poles?
– Magnetic Domains
• How can a magnet loose some of its magnetic properties?
– Heat it or Drop it
Uses of Magnetic fields
• Hans Christian
Oersted – observed
that a current moving
through a wire moved
the needle on a nearby
compass; moving
electric charges create
a magnetic field.
Uses of Magnetic fields
Solenoid – coil
of currentcarrying wire
that produces
a magnetic
field
Uses of Magnetic
fields
• Electromagnet –
strong, temporary
magnet made by
inserting an iron
core into a wire
coil & passing an
electric current
through the coil.
Strength of electromagnet can
be increased by:
• inserting iron core
• adding more turns to the wire
• increasing the
amount of current
Electromagnetic Devices
• Electromagnets
change electrical
energy to
mechanical
energy
Motor
using an electromagnet
to turn an axle
•Commutator –
reversing switch
Electromagnetic
Devices
• Galvanometer –
detects electric
current, using a
solenoid
Generating Electric
Current
• Michael Faraday
discovered
electromagnetic
induction; according to his
law, a voltage is induced
in a conductor by a
changing magnetic field
Electromagnetic induction
Generating Electric Current
• Generators –
produce
electric current
by rotating a
loop of wire in
a magnetic
field.
Generators
• Mechanical
energy
produces
electrical
energy
FORCE
• Moving electric charges
produce magnetic force
• Moving magnets produce
electric force
Two types of generators
1. Direct current (DC) - current
flows in one direction, example
is dry cell batteries
2. Alternating current (AC) current reverses direction in a
regular pattern
Transformers
1. Step-up
• Increases voltage
• More coils in secondary coil
2. Step-down
• Decreases voltage
• More coils in primary coil
Transformers
Voltage converters like in USA, Europe,
Asia, Africa, Australia
Superconductors
• Material that has no electrical resistance
• Occurs at OK
Advantages
• current flows indefinitely
• eliminates electrical waste
Disadvantages
• brittle, hard to shape into wires
• need to be cold in order for it to work
LAST Star questions
•
•
•
•
•
•
•
•
•
Reversing switch
Commutator
Compasses point here
Magnetic north
A transformer that increases voltage
Step-up transformer
Material which has no electrical resistance
Superconductor
STUDY VOCABULARY!!!!!