1. Physical Science Chapter 18
Magnetism
Physical Science
Chapter 18

2. physical science chapter 18
Magnets
Pull iron (and some other metals) towards them.
When small and allowed to rotate freely, always point north (compasses).
physical science chapter 18

3. physical science chapter 18
Magnetism
A property of matter in which there is a force of repulsion or attraction between like or unlike poles.
Related to electricity.
physical science chapter 18

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Magnetic poles
The ends of magnets
Where the magnetic forces are strongest
Like poles repel
North and north or south and south
Opposite poles attract
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Permanent magnets
Naturally magnetic
Retain magnetic properties for long periods of time.
Made of materials like iron, cobalt, and nickel
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Temporary magnets
Formed by objects being near or rubbing against a permanent magnet
Lose their magnetic properties soon after being separated from permanent magnet.
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Magnetic field
The area around a magnet where magnetic forces act.
Strongest near the poles.
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Compass
Magnetic needle that rotates freely
Lines up with the Earth’s magnetic field.
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9. physical science chapter 18
Discuss
Section 1 Review question #4 on page 624
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10. Creating magnetic fields
An electric current causes a magnetic field.
The direction of the current affects the direction of the magnetic field.
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Electromagnets
Magnets created by electric current flowing through wires
When a wire is coiled into a solenoid, a strong magnetic field is created in the coil.
Inserting an iron core inside the solenoid increases the magnetic field.
See page 627
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12. physical science chapter 18
Galvanometer
Instrument used to detect currents.
A coil of wire around an iron core with a needle.
Between permanent magnets.
When there is current in the wire, the magnetic forces cause it to rotate, moving the needle.
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Ammeters
Galvanometers calibrated to measure current.
Connected in series with the circuit.
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Voltmeters
Galvanometers calibrated to measure potential difference.
Connected in parallel with the circuit
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Electric motor
Contains an electromagnet that can rotate.
Rotates between opposite poles of a permanent magnet.
The current produces a magnetic field that makes the coil turn.
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Electric motor
To keep the coil turning, the direction of the current in the coil must be reversed after every half turn.
Done by a reversing switch called a commutator
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17. physical science chapter 18
Discuss
Describe an electromagnet.
What is an instrument that can be used to measure either current or potential difference?
What does an ammeter measure?
What does a voltmeter measure?
What is a commutator?
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18. Electromagnetic induction
Moving a wire through a magnetic field produces a current in the wire
You can also move a magnet through a coil of wire to produce a current in the wire
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Generators
Use electromagnetic induction to make current (electricity)
A loop of wire is rotated in a magnetic field.
It needs mechanical energy to make it rotate
Usually comes from burning fuel
Similar to an electric motor, but with the opposite function
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Direct current DC
From batteries
Current only flows in one direction in the wire
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Alternating current AC
Wall outlets
Current reverses direction in a regular pattern
In US, reverses 120 times per second for 60 Hz alternating current
Most appliances have built in converters that change AC to DC.
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Transformer
Increases or decreases the voltage of AC current
Uses two coils with different numbers of turns
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23. Step-down transformer
Reduces voltage
Used between power lines and home electrical circuits
High voltage electricity travels more efficiently, but is not good for household appliances
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24. physical science chapter 18
Discuss
Describe electromagnetic induction.
A generator operates by changing _____________ energy into ____________ energy.
Which kind of current reverses its direction in a regular pattern?
Describe a step-down transformer.
physical science chapter 18