Download Circular Motion HW-1

AP Physics-1
Circuits HW-2 (“Resistors in Series & Parallel”):
due___________
Read Textbook Sections 23-1, 23-2, 23-3, 23-4, & 23-5
Conceptual Questions
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Are car headlights connected in series or parallel? Give an everyday observation that supports your answer.
Two resistors are connected in parallel. If a third resistor is connected in parallel with the other two, does the
equivalent resistance of the combination increase, decrease, or remain the same? Explain.
The resistivity of tungsten increases with temperature. (a) When a light containing a tungsten filament heats up,
does its power consumption increase, decrease, or stay the same? Explain. (b) Why do tungsten filaments tend
to “burn out” just as they are turned on rather than after they have been on a while?
Is it possible to connect a group of resistors of value R in such a way that the equivalent resistance is less than
R? If so, give a specific example.
Give an example of how four resistors of resistance R can be combined to produce an equivalent resistance of R.
Light A has twice the power rating of light B, and this rating is under the assumption that all bulbs will be
connected to the same voltage. How does the resistance of light A compare with that of light B?
What physical quantity do resistors connected in series have in common? (A one-word answer suffices.)
What physical quantity do resistors connected in parallel have in common? (A one-word answer suffices.)
Explain how electrical devices can begin operating almost immediately after you throw a switch, even though
individual electrons in the wire may take hours to reach the device.
An electric heater has a power rating of 500 W when connected to a given voltage V. If two of these heaters are
connected in series to the same voltage, is the total power consumed by the two heaters greater than, less than, or
equal to 1000 W? Explain.
Problems
Resistors in Series and Parallel
1. Find the equivalent resistance between points A and B for the group of resistors shown in Figure 1.
2. What is the minimum number of 65-  resistors that must be connected in parallel to produce an equivalent
resistance of 11  or less?
3. Four light bulbs (A, B, C, D) are connected together in a circuit of unknown arrangement. When each bulb is
removed one at a time, the following behavior is observed:
A
B
C
D
A removed
*
on
on
on
B removed
on
*
on
off
C removed
off
off
*
off
D removed
on
off
on
*
Each bulb is replaced before a subsequent bulb is removed. Draw a circuit diagram for these bulbs.
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A circuit consists of a 9.0-V battery connected to three resistors ( 42 , 17 , and 110  ) in series. Find
(a) the current that flows through the battery, (b) the current that flows through each resistor, and
(c) the potential difference across each resistor.
A circuit consists of a battery connected to three resistors ( 65 , 25 , and 170  ) in parallel. The total
current through the resistors is 1.3 A. Find (a) the emf of the battery, (b) the voltage across each resistor, and
(c) the current through each resistor.
Find the equivalent resistance between points A and B shown in Figure 2.
Figure 1
Figure 2
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The circuit in Figure 3 includes a battery with a finite internal resistance, r  050
. . (a) Find the current
flowing through the 71
. -  resistors. (b) How much current flows through the battery?
. - and the 32
(c) What is the potential difference between the terminals of the battery?
Figure 3
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The terminals A and B in Figure 2 are connected to a 9.0-V battery. (a) Find the current flowing through each
resistor. (b) Is the potential difference across the 6.3 -  resistor greater than, less than, or the same as the
potential difference across the 1.5- resistor? Explain.
Figure 2
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The current flowing through the 845
. - resistor in Figure 4 is 1.22 A. (a) What is the voltage of the battery?
(b) If the 17.2 - resistor is increased in value, will the current provided by the battery increase, decrease, or
stay the same? Explain.
Figure 4
Answers
R = 33 
n = 6 resistors (must be rounded up to whole number of resistors)
circuit diagram with four resistors properly arranged
(a) Itot = 53 mA (a) I42 = I17 = I110 = 53 mA (c) V42 = 2.2 V, V17 = 0.91 V, V110 = 5.9 V
(a)  = 21 V
(b) V65 = V25 = V170 = 21 V
(c) I65 = 0.33 A, I25 = 0.85 A, I170 = 0.12 A
Req = 0.838 
(a) I3.2 = 1.1 A, I7.1 = 0.3 A
(b) Ibattery = 1.4 A
(c) Vbattery = 11.3 V
(a) I1.5 = 6.0 A, I2.5 = 3.6 A, I6.3 = 1.1 A, I4.8 = 0.38 A, I3.3 = 0.55 A, I8.1 = 0.22 A
(b) A potential difference exists across the 3 resistor parallel combination that is in series with the 6.3 
resistor, resulting in a potential difference less than 9.0 V across the 6.3  resistor.
9. (a)  = 103.9 V
(b) Increasing the resistance of one of the parallel paths increases the total resistance of the parallel section.
Since it is in series with the other two resistors, the equivalent resistance of the circuit increases, causing a
decrease in the current in the circuit.
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