Transcript Magnetic Field

Magnetism
Mole
A-Train
Kenny
Johnny Wang
Which items below use magnets and which do
not?
hair dryers
buzzers
computers
dishwashers
Fans
dryers
blenders
electric can openers
Motors
generators
alternators
Television set
Alarm clocks
Watches
Doorbells
Speakers
Mole
Cranes
A-Train
Kenny
Johnny Wang
Radios
Automatic doors
bells
Law of Magnetic Poles
All magnets have 2 poles. A North pole and a
South pole. These poles exert magnetic forces
on each other.
South
Repel
South
North
Repel
North
South
Attract
North
Earth as a Magnet
The earth has 4 recognized poles
1. Geographic North
2. Geographic South
3. Magnetic North
4. Magnetic South
Axis Poles
Magnetic
Poles
Magnetic Materials
• Iron (magnetite)
• Nickel
• Cobalt
• Gadolinium
These materials can
either attract to magnets
or be made into magnets
according to the Domain
Theory of Magnetism
Iron
Nickel
Cobalt
Gadolinium
Magnetic Field
- The region around a magnet where
invisible lines of force are acting. Field
gets weaker as you get farther away.
_
+
Mole
A-Train
Kenny
Johnny Wang
Link
N
S
Magnetosphere:
The name given to the earth’s
magnetic field.
• Magnetism is strongest at the poles
• Has reversed many times in history
• Protects the earth from harmful radiation
from sun
• Causes glowing lights at poles (auroras)
– Aurora Borealis (northern lights)
– Aurora Australis (southern lights)
http://www.scienceteacherprogram.org/physics/Omoloju04.html
http://www.coolmagnetman.com/maghow.htm
Domain Theory of Magnetism
Any magnetic material is made up of
tiny magnetic domains that have poles.
If the poles of these domains are
aligned, then the entire material will
have poles and a magnetic field.
An atom that has its electrons
spinning in the same direction
will have a magnetic field. A
group of these atoms with their
poles aligned make up a domain.
North
North
South
South
PERMANENT MAGNETS
Bar
Domains
Magnet
Electromagnetism
-magnetism created from the flow
of electric current through a
conductor. Field demo
Demo 2
Temporary Magnets: Magnetism that can be turned on and off.
Three basic parts of an
electromagnet
1. Electric current (AC or DC)
2. Core
3. Coiled wire
All which can be increased
or decreased.
Direct Current
• Electric current that travels only in one
direction.
– Produced by chemical reactions (batteries)
– Low intensity
Alternating Current
• Electric current that travels back and forth
in a circuit.
– Changes direction 60 times in a second!!!
– Much more intense the Direct Current
– Created by a generator (magnets inside)
– Can travel great distances
The Electric Motor
A device that converts electrical
energy into mechanical energy.
Parts of a motor
• Armature (the electromagnet)
• Permanent magnets (attached
to the inside of motor case)
• Brushes ( bring electricity into
motor, rub the commutator)
• Commutator ( switches
direction of current, switching
poles of e-magnet)
N
El e ct r i c
Cu r r e n t
El e ct r i c
Cu r r e n t
N
Poles of an electromagnet change
El e ct r o min
a g the
n et M
o d uchanges
le
when the current
coil
!!!!!
El e ct r i c
Eye
Co i l o f W i r e
A ttr a ct
Rep el
Ro to r
Motor Applet
Armature
M a g n ets o n th e o u tsi d e (sta
to r )
link
Cl e a r = n o r t h p o l e
C
B
N
A
it o n
Ro
t
a
Sw i tch
Bl a ck = so u t h p o l e
C
N
A
B
Armature axle
Brushes
Brushes
Brushes
Commutator
Permanent Magnets
Electric Generator
A device that converts mechanical
energy into electrical energy.
Generator link
Electric Generators
Mechanical
energy in
Electrical
energy out
Falling water (hydro)
Wind
Steam
Steam from earth
Nuclear power (steam)
Fossil Fuels (steam)
Tides
Ocean waves
Electricity
Transformers
A device that changes the voltage of
alternating current
A transformer that increases
current is called a Step-up
transformer.
A transformer that decreases
current is called a Step-down
transformer.