AP Physics B1
Chapter 18- Electric Circuits
Questions for Discussion
Series Circuits, Parallel Circuits and Networks (Sections 18.1 to 18.7)
1. A current of 2.8 amps flows for 15 s. How many electrons pass through the circuit?
The magnitude of the electron charge is 1.60 x 10 –19 C.
2.
I.
II.
€
III.
IV.
Match each description with a graph.
(a) Voltage vs. current graph for a constant resistance circuit.
(b) Current vs. resistance graph for a circuit whose source has constant emf.
3.
10 Ω
€
8.0 Ω
€
2.0 Ω
€
60 V
€
(a) What current flows in the circuit?
(b) What is the potential difference across the 10 Ω resistor?
€
4. A circuit consists of a battery and a 15 Ω resistor. What resistor should be added in series
3
with the 15 Ω resistor to reduce the current to of its original value?
4
5.
R
€20 Ω
€
€
€
81 V
€
I= 3.0 A
The current I that flows through the circuit is 3.0 A.
(a) What is the voltage drop across resistor R?
(b) What is the value of R?
6. As more resistances are connected in parallel with a source whose emf is constant
(a) the equivalent resistance of the circuit (increases, decreases, remains the same).
(b) the total current drawn by the circuit (increases, decreases, remains the same).
(c) the current flowing through the first resistor (increases, decreases, remains the same).
7. A 12 Ω resistor is connected in parallel with an R Ω resistor. What is the value of R if
the total current flowing through the two resistors flows through the 12 Ω resistor?
3
of
4
€8. A 12 Ω resistor, 20 Ω resistor and an R€Ω resistor are connected in parallel across a 60 V
source. The three resistors draw a total of 10 A from the source. What is the€
value of R?
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€
€ €
€
€
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9.
I= 7.0 A
V
36 Ω
2.5 A
RΩ
€
€
The current that flows through the 36 Ω resistor is 2.5 A. The current I supplied by the source
is 7.0 A.
(a) What is the voltage V of the source?
(b) What is the value of R?
€
I= 6.0 A
10.
V
4.0 Ω
€
12 Ω
€
The current supplied by the source is 6.0 A.
(a) What is the voltage of the source?
(b) How much current goes through the 4.0 Ω resistor?
(c) How much current goes through the 12 Ω resistor?
11. List the equivalent resistance of each possible network that could be formed using three 18 Ω
resistors.
€
€
€
12. Solve the network and complete the table.
R 3 = 30 Ω
R1 = 30 Ω
€
9.0 Ω
6.0 Ω
€
€
€
R 2 = 20 Ω
3.0 Ω
40 Ω
120 V
€
R 4 = 20 Ω
€
4.0 Ω
€
2.0 Ω
€
€
€
35 Ω
Resistor
Potential
€
Drop (Volts)
Current
€
(Amperes)
5.0 Ω
Resistor
R1 = 30 Ω
3.0 Ω
R 2 = 20 Ω
2.0 Ω
€
R 3 = 30 Ω
€
R 4 = 20 Ω
€
9.0 Ω
€
4.0 Ω
€
6.0 Ω
€
40 Ω
€
35 Ω
€
€
€
€
€
5.0 Ω
Potential
Drop (Volts)
Current
(Amperes)
13.
1
2
3
4
The circuit shown above contains five identical light bulbs. The more current passing through
a bulb, the brighter the bulb for identical light bulbs. Suppose Bulb 3 is unscrewed, removing
it from the circuit.
(a) As a result, the bulb 1 (gets dimmer, gets brighter, goes out).
(b) As a result, the bulb 2 (gets dimmer, gets brighter, goes out).
(c) As a result, the bulb 4 (gets dimmer, gets brighter, goes out).
14.
120 V
R
Every resistor in the above circuit has a resistance of 2.0 Ω. Find the current that flows
through the resistor labeled R.
15.
I
A
B
There are two resistors in parallel with a source of constant emf in the above circuit. As the
number of resistors in parallel increases,
(a) the current I (increases, decreases, remains the same).
(b) the potential difference V A – V B (increases, decreases, remains the same).
16.
20 Ω
€
10 Ω
30 Ω
Rank the currents that flow through each resistor from smallest (number 1) to largest. If the
same current flows through more than one resistor then assign the same number to each of
those resistors.
10 Ω
20 Ω
30 Ω
17.
I
1
2
3
Suppose bulb 3 burns out in the series circuit shown above. Will bulbs 1 and 2 remain lit
because they get current before it reaches bulb 3? Explain.
18.
Circuit A
Circuit B
R
V
2R
V
R
2R
R
2R
(a) The voltage across each resistor in circuit A is (less than, equal to, greater than) the
voltage across each resistor in circuit B.
(b) The current flowing through each resistor in circuit A is (less than, equal to, greater than)
the current flowing through each resistor in circuit B.
19. Why doesn’t a bird get electrocuted when it lands on an uninsulated high voltage power line?
20.
2
4
5
1
3
6
Each of the bulbs in the circuit is identical. The brightness of a bulb increases with the power
dissipated by the bulb. For identical resistors, the greater the current passing through a resistor
the greater the power dissipated by the resistor. Rank the bulbs from least bright (number 1)
to brightest. If more than one bulb has the same brightness then assign each of those bulbs the
same number.
Bulb 1
Bulb 2
Bulb 3
Bulb 4
Bulb 5
Bulb 6
21.
1
3
2
4
Each of the bulbs in the circuit is identical. The brightness of a bulb increases with the power
dissipated by the bulb. For identical resistors, the greater the current passing through a resistor
the greater the power dissipated by the resistor. Suppose Bulb 3 in the above circuit is replaced
by a straight wire, leaving Bulb 4 as the only resistance in the right branch of the circuit.
(a) The brightness of Bulb 1 (increases, decreases, remains the same) as a result.
(b) The brightness of Bulb 2 (increases, decreases, remains the same) as a result.
(c) The brightness of Bulb 4 (increases, decreases, remains the same) as a result.
22. Car batteries are rated in ampere-hours. What does this rating tell you about the battery?
23.
R
In the laboratory, a student wishes to find the resistance of a resistor. The student sets up a
series circuit consisting of a source, the unknown resistance R and a variable resistor (the arrow
passing through the symbol of a resistor indicates that the resistor is a variable resistor). The
student alters the resistance of the variable resistor so that the current passing through the
unknown resistance varies. The current passing through the unknown resistance and the
corresponding voltage across the unknown resistor are measured with meters. The results are
shown below.
Current (A)
Voltage (V)
.70
1.8
2.1
5.3
2.4
5.9
3.0
7.6
3.4
8.4
(a) Show how to connect a voltmeter and an ammeter to the above circuit so that current
through the unknown resistor and voltage across the unknown resistor can be measured.
(b) Plot the data and draw a best fit line through the plotted points.
(c) What is the value of the unknown resistance R? Explain how you obtained your result.