Amazingly Tempting Future Exam Question:
If someone were to walk up to you and ask for a “lay-person’s”
explanation of electric current (what we mean by that word, and how
it works), what would you say?
5/5/17
Oregon State University PH 213, Class #15
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Why does the light in a room come on instantly when you flip a
switch several meters away?
A. Electrons travel at the speed of light through the wire.
B. Because the wire between the switch and the bulb is already full of
electrons, a flow of electrons from the switch into the wire
immediately causes electrons to flow from the other end of the
wire into the light bulb.
C. The switch sends a radio signal which is received by a receiver in
the light which tells it to turn on.
D. Optical fibers connect the switch with the light, so the signal
travels from switch to the light at the speed of light in an optical
fiber.
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Oregon State University PH 213, Class #15
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Another Pretty Good Future Exam Question:
If someone were to walk up to you and ask for a “lay-person’s”
explanation of electrical resistance (what we mean by that word, and
how it works), what would you say?
5/5/17
Oregon State University PH 213, Class #15
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Figure 30.8A
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Oregon State University PH 213, Class #15
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Figure 30.8B
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Oregon State University PH 213, Class #15
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What happens IN the wire?
• Voltage difference means
there is an electric field.
• Electric field means charges
feel force.
• Free charges in conductors
can move: CURRENT!
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Oregon State University PH 213, Class #15
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Figure 30.2
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Oregon State University PH 213, Class #15
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Oregon State University PH 213, Class #15
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Oregon State University PH 213, Class #15
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Figure 30.4
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Oregon State University PH 213, Class #15
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Figure 30.7
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Oregon State University PH 213, Class #15
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A working model of current and resistance:
Put the pieces together
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Oregon State University PH 213, Class #15
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Figure 30.13
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Oregon State University PH 213, Class #15
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Oregon State University PH 213, Class #15
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Figure 30.20A
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Oregon State University PH 213, Class #15
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Figure 30.20B
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Oregon State University PH 213, Class #15
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