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Chapter 22
Current and Resistance
Topics:
• Current
• Conservation of current
• Batteries
• Resistance and resistivity
• Simple circuits
Sample question:
How can the measurement of an electric current passed through a
person’s body allow a determination of the percentage body fat?
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 22-1
Chapter 22: Summary
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Slide 22-38
Batteries
The potential difference
between the terminals of a
battery, often called the
terminal voltage, is the
battery’s emf.
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Slide 22-20
Escalator model for batteries
Another way of understanding
series and parallel components
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Slide 22-25
Voltage loop graph (See Example 22.10 in text)
(1 bulb and 2 bulbs)
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Slide 21-16
Conservation of Current
å Iin = å Iout
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Slide 22-15
Checking Understanding
Rank the bulbs in the following circuit according to their brightness,
from brightest to dimmest.
A.
B.
C.
D.
A>B=C>D
A=B=C=D
A=D>B=C
B=C>A>D
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 22-16
Answer
Rank the bulbs in the following circuit according to their brightness,
from brightest to dimmest.
A.
B.
C.
D.
A>B=C>D
A=B=C=D
A=D>B=C
B=C>A>D
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 22-17
Bulbs in Parallel Demo???
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Slide 22-25
Kirchhoff’s Laws
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Slide 23-11
Voltages around a loop in the circuit
(2 bulbs and 3 bulbs)
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Slide 21-16
Simple Circuits
The current is determined by
the potential difference and
the resistance of the wire:
∆V
_____
chem
I = R
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Slide 22-13
Power in Circuits
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Slide 22-19
Energy and Power in Resistors
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Slide 22-31
Checking Understanding
A resistor is connected to a 3.0 V battery; the power dissipated in
the resistor is 1.0 W. The battery is now traded for a 6.0 V battery.
The power dissipated by the resistor is now
A. 1.0 W
B. 2.0 W
C. 3.0 W
D. 4.0 W
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 22-20
Answer
A resistor is connected to a 3.0 V battery; the power dissipated in
the resistor is 1.0 W. The battery is now traded for a 6.0 V battery.
The power dissipated by the resistor is now
D. 4.0 W
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 22-21
Electric Blankets
1. An electric blanket has a wire that runs through the interior. A
current causes energy to be dissipated in the wire, warming the
blanket. A new, low-voltage electric blanket is rated to be used at
18 V. It dissipates a power of 82 W. What is the resistance of the
wire that runs through the blanket?
2. For the electric blanket of the above example, as the temperature
of the wire increases, what happens to the resistance of the wire?
How does this affect the current in the wire? The dissipated
power?
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Slide 22-22
Additional Clicker Questions
1. A set of lightbulbs have different rated voltage and power, as
in the table below. Which one has the highest resistance?
Bulb
A
B
C
D
E
Rated voltage
10 V
8V
12 V
6V
3V
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Rated power
1W
1W
2W
2W
3W
Slide 22-23
Answer
1. A set of lightbulbs have different rated voltage and power, as
in the table below. Which one has the highest resistance?
Bulb
A
Rated voltage
10 V
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Rated power
1W
Slide 22-24