Transcript Magnetism - Worth County Schools

Magnetism
What is the
relationship between
magnetism and
electricity?
Jack T. Duncan
Physical Science
EQ1: What is magnetism?
Magnetism – the properties and interactions
of magnets
1. All magnets have magnetic forces – ability to
attract or repel.
2. The magnetic field surrounds a magnet and
exerts magnetic lines of force.
- stronger when closer to magnet
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EQ2: How do magnets behave?
Magnetic poles – regions of magnet where
the magnetic forces are the strongest
- magnetic lines are the most numerous
1. All magnets have a north(N) and south(S)
pole.
- Two unlike poles (N-S) – attract
- Two like poles (N-N & S-S) – repel
* make drawings

Earth’s magnetic poles
2. The earth has north and south magnetic poles.
- different locations than the earth’s
geographic poles ( N magnetic pole – Canada)
- the compass – is a freely rotating magnetic
needle that responds to the earth’s magnetic
poles by pointing North.
- Lodestone (magnetite) – a natural magnet
was used as the first compass on ships.
Magnetic materials
3.Magnets (natural and man-made) are usually
made up of ferromagnetic materials such as
iron, nickel, cobalt and steel.
- only strongly attracted to these ferromagnetic
materials; has little or no attraction for other
types of materials.
Magnetic domains
4. Magnetic domains – groups of atoms that
behave like tiny magnets.
- If magnetized – domains line up in same
direction
- If un-magnetized – domains remain in a
random arrangement
* make drawings
Unmagnetized Material
Magnetized Material
Permanent magnets

Permanent magnets – made by placing
magnetic materials in a strong magnetic field
causing a magnetic domains to line up.
- most are made of iron/steel and a
combination of other elements
- Ex. Alnico – very strong permanent magnet
- magnetism can be destroyed by heating,
striking the magnet, and over long time periods
Temporary magnets

Temporary magnets – are made up of
magnetic materials but do not last a long time
- by making contact with a magnet
- by stroking the material in same direction
with a permanent magnet
- by using electricity (electromagnet)
EQ3: What is electromagnetism and
why is it so important?

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Electromagnetism – the force created by the
relationship and interaction between electricity
and magnetism.
Contributions by two important scientists:
1. Hans Christen Oersted - 1820
- a Danish physicist who discovered that an
electric field in his experiment set up a
magnetic field and affected a nearby compass.
Electromagnetism
2. Andre Marie Ampere – 1821
- a French physicist who discovered that coils
or loops of conducting wire carrying current
produces an even stronger magnetic field.
- the more coils or loops, the stronger the
magnetic field
Electromagnetism
In 1825, scientists discovered the first
electromagnet.
 Electromagnet – a temporary magnet produced
with a soft iron core material surrounded by
coils or loops of wire(solenoid) that is
controlled by electricity.
- ways to increase the strength: 1) increase
coils 2) increase current & 3) larger iron cores
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Uses of electromagnets

Many common and important uses of
electromagnets:
1.Telephones
2. Doorbells
3. Stereo speakers
4. Pick up scrap metal (using a crane)
5. Electric motor*
EQ5: How does the electric motor
work?
Electric motor – a device that changes
electrical energy into mechanical energy
1. The electromagnet is free to rotate between
the poles of a permanent fixed magnet.
2. Electric current flowing around the coils of an
electromagnet sets up a magnetic field.
3. Changing direction of current causes the poles
to constantly reverse and rotate.
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Electric motors
4. The rotating electromagnet is connected to a
shaft that turns parts or gears for motion.
• Electric motors are found in many appliances
and tools that have moving parts:
Ex. Fans, mixers, washing machines, drills,
saws, toys etc.
EQ6. What is electromagnetic induction and
why is it so important?

1.
2.
Electromagnetic induction (induced current)
- the production of an electric current from a
magnetic field.
Two ways:
Moving a loop or coil of wire through a
magnetic field.
Moving a magnet through a loop of wire.
Electromagnetic induction
Contributions by two important scientists;
1. Michael Faraday – 1831
- an English scientist who discovered that an
electric current could be caused by moving a
wire through a magnetic field.
2. Joseph Henry – an American scientist made a
similar discovery
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Electromagnetic induction
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As a conducting wire cuts through the
magnetic lines of force, it induces an electric
current (Faraday’s law).
Galvanometer – instrument used to detect and
measure very small amounts of electric current
The discovery of electromagnetic induction led
to important inventions such as the electric
generator and transformers.
EQ7: How does the electric
generator work?

Generator – a device that produces electricity
from mechanical energy by rotating a coil of
wire in a magnetic field.
- the coil is rotated by an outside source of
mechanical energy.
- as the coils rotate within the magnetic field, an
electric current flows through the coil.
Generator
- The coils of the electromagnets are connected
to a turbine – large wheel with blades that
rotates when pushed by water, steam or wind.
- The direction of the coil changes twice with
each revolution – producing alternating current
(AC)
 At power plants generators produce AC at a
rate of 60 cycles/second or 60 Hz – changing
direction 120 times/second.
EQ8: How does a transformer
work?
Transformer – a device that increases or
decreases the voltage of AC.
- made of two coils (primary and secondary)
wrapped around the same iron core.
- changes of current in the primary coil
(incoming voltage) induces a change in the
current in the secondary coil (outgoing
voltage).
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Transformer
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Two types of transformers:
1. Step-up transformer – the secondary coil
has more loops or coils than the primary coil.
- it increases the voltage
- located at power plants and along the
route at power substations to boost it up to
travel long distances
Transformer
2. Step-down transformer – the primary coil has
more loops or coils than the secondary coil.
- it decreases the voltage
- located on utility poles (round bucket) and
used for certain appliances and toys (trains).
- can reduce very high voltage from power
lines (750, 000 V) down to household use of
110 – 220 V of AC.
Transformers