Download Chapter 8 Section 2

And Electricity!
Chapter 8 Section 2
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1820: Hans Ørsted happened to have
compass close to a wire with current flowing
The compass needle deflected away from
magnetic north when the current was turned
on and returned when the current was turned
off
Hypothesis: magnetic field radiates in all
directions from a wire carrying an electric
current
Based on Ørsted’s work we know electricity
and magnetism are related
 Any moving charge produces a magnetic field
Direction of magnetic field around wire
depends on direction of current
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If we loop a wire around a metal center, we
amplify the magnetic field created by the
current
Electromagnet is a temporary magnet
created in this way
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If we reverse the current, the poles of the
electromagnet are reversed
Electromagnets can be turned on or off by
turning the current on or off
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Electromagnets are used in many devices:
 Speaker:
▪ Has a permanent magnet attached to a cone
▪ Has an electromagnet
▪ When electromagnet changes poles, it is attracted or
repelled by the permanent magnet
▪ Movement of the cone makes sound
▪ HowStuffWorks "How Speakers Work"
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Galvanometer
 Galvanometer has a fixed magnet and a coil of
wire making an electromagnet
 When current goes through electromagnet it is
attracted or repelled by fixed magnet so it moves
 Needle attached to moving coil measures amount
of current
▪ Voltmeter
▪ Ammeter
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Electric motor
 Electromagnet that can rotate between poles of
permanent magnet
 Current through electromagnet makes it
attracted and repelled to poles of permanent
magnet
 HowStuffWorks "How does a brushless electric
motor work?“
 YouTube - Direct Current Electric Motor
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Read pages 233-239
Answer questions 1-6 on page 239: due
12/2/09