Honors Physics
Worksheet
Chapter 17-18 Electric Circuits and Power
1. Suppose the current in a floodlamp is 5.0 A. What charge passes through the lamp in 3.0 s?
(Answer: 15 C)
2. A total charge of 4800 C passes each point in a circuit in 16 minutes. What steady current
flows in this circuit? (Answer: 5.0 A)
3. (a) The opposition to the flow of current is called ____. (Answer: resistance)
(b) The unit of resistance is the ____. (Answer: ohm)
(c) The opposition to the flow of current is a process that converts electrical energy into ____.
(Answer: heat)
4. (a) Current in a resistor flows from (high potential to low potential, low potential to high
potential). (Answer: high potential to low potential)
(b) Current in a battery or other source of electrical energy flows from (high potential to low
potential, low potential to high potential). (Answer: low potential to high potential)
5. True or False
Current cannot flow in a circuit unless a complete conducting path exists in the circuit.
(Answer: True)
6. When the potential difference across a lamp is 12 V, the current passing through the lamp
is 4.0 A. What is the resistance of the lamp? (Answer: 3.0 Ω)
7. What is the potential difference across a 10 Ω resistor carrying a current of 2.0 A?
(Answer: 20 V)
€
8. The potential difference across a 2.0 Ω resistor is 4.0 V. What current is flowing through the
€
resistor? (Answer: 2.0 A)
€
9. Name each unit and then express each in MKS units.
€
kg •m 2
(a) the unit of potential (Answer: volt=
)
C •s2
C
(b) the unit of current (Answer: ampere= )
s
kg •m 2
€
(c) the unit of resistance (Answer: ohm=
)
C 2 •s
€ an electrical device, there is a potential drop of 42 V
10. When 1.4 A of current flows through
across the device. If 2.2 A of current flows through the device then what would be the potential
difference across the device? (Answer:
66 V)
€
11. Each circle represents either a voltmeter or ammeter. Identify each meter assuming it is
correctly connected.
Answers:
G
Meter
H
J
Type
G
Ammeter
H
Ammeter
I
Voltmeter
J
Ammeter
K
Voltmeter
6.0 V
2.0 Ω
I
€
12. (a)
(b)
(c)
(d)
2.0 Ω
€
The resistance of a voltmeter is (high, low). (Answer: high)
Voltmeters are connected in (series, parallel) with a circuit element. (Answer: parallel)
The resistance of an ammeter is (high, low). (Answer: low)
Ammeters are connected in (series, parallel) with a circuit element. (Answer: series)
13. What is the equivalent resistance of the combination?
6.0 Ω
10 Ω)
(Answer:
€
€
K
1.0 Ω
€
3.0 Ω
€
14. Resistors R1 , R 2 , R 3 and R 4 are equal in value. What do voltmeters A, B and C read assuming
connecting wires in the circuit have negligible resistance?
Voltmeter A
€
Voltmeter B
V
V
R1
€
Voltmeter C
V
R2
€
R3
€
R4
€
12 V
(Answer: Voltmeter A reads 3.0 V, Voltmeter B reads 3.0 V and Voltmeter C reads 6.0 V)
15. A circuit consists of a battery and a 20 Ω resistor. What resistor should be added in series
2
with the 20 Ω resistor to reduce the current to of its original value? (Answer: 10 Ω )
3
€
16. The resistance of a large resistor
is 5.0 times the resistance of a small resistor. The resistors
are
connected
in
series
across
a
120
V source. What is the potential drop
€
€ across the large
resistor?
€
(Answer: 100 V)
€
17. (a) Suppose V is the potential difference across a resistor R carrying a current I. Write an
equation relating V, I and R. (Answer: V= IR)
Consider the following circuit in parts (b), (c) and (d).
V4
€
A
2.0 Ω
X
Y
V1
V2
V3
€
(b) If voltmeter V1 reads 4.0 V then what is the reading of ammeter A? (Answer: 2.0 A)
(c) If resistor X equals 3.0 Ω then what is the reading of voltmeter V 2 ? (Answer: 6.0 V)
€
€
€
(d) If voltmeter V 4 reads 12 V then what is the value of resistor Y? (Answer: 1.0 Ω)
€
€
€
€
€
18. Solve the network.
5.0 Ω
R
€
36 V
I= 3.0 A
Answer:
3.0 A
15 V
5.0 Ω
€
3.0 A
21 V
7.0 Ω
€
36 V
I= 3.0 A
19. Solve the network.
15 V
6.0 Ω
R
2.5 A
15 V
6.0 Ω
2.5 A
35 V
14 Ω
€
50 V
€
Answer:
€
50 V
€
€
20. Solve the network.
10 Ω
€
8.0 Ω
€
2.0 Ω
€
50 V
€
Answer:
25 V
2.5 A
10 Ω
20 V
2.5 A
8.0 Ω
€
€
€
€
50 V
€
21. Find the equivalent resistance of each combination.
(a)
3.0 Ω
€
6.0 Ω
(Answer: 2.0 Ω)
€
€
5.0 V
2.5 A
2.0 Ω
(b)
12 Ω
€
6.0 Ω
€
4.0 Ω
€
(Answer: 2.0 Ω)
22. A 12 Ω coil and a 6.0 Ω coil are connected in parallel. A total current of 3.0 A passes through
the coils.
(a) €
What is their combined resistance? (Answer: 4.0 Ω)
(b) What current flows through the 6.0 Ω coil? (Answer: 2.0 A)
€
€
23. (a) What current flows through the 7 Ω resistor?
€
7Ω
€
€
8Ω
€
€
9A
4Ω
€
6A
(Answer: 3 A)
(b) Kirchhoff’s Current Law
The sum of the currents arriving at any branch point in a circuit equals the sum of the
currents leaving the branch point. This rule is based on what fundamental principle?
(Answer: Conservation of charge)
(c) According to Kirchhoff’s Current Law, if resistors are connected in ____ then the
current in each resistor will be ____.
(Answer: first blank- series, second blank- equal)
(d) According to Kirchhoff’s Current Law, if resistors are connected in ____ with a
source then the current leaving the source will equal the sum of the currents flowing
through the resistors. (answer: parallel)
24. (a) The potential difference between point A and point B is 12 V. What is the potential
difference across the 7 Ω resistor?
XΩ
€
A
€
3V
7Ω
€
€
YΩ
5V
B
(Answer: 4 V)
(b) Kirchhoff’s Voltage Law
The sum of the voltages around any closed loop in a circuit is zero. This rule is based on
what fundamental principle?
(Answer: Conservation of energy)
(c) According to Kirchhoff’s Voltage Law, if resistors are connected in _____ with a battery
then the voltage across the battery will equal the sum of the voltages across the resistors.
(Answer: series)
(d) According to Kirchhoff’s Voltage Law, if resistors are connected in _____ with a battery
then the voltage across each resistor will equal the battery voltage. (Answer: parallel)
25. True or False
If two resistors are connected in parallel then the equivalent resistance of the combination is
less than either of the two resistors. (Answer: True)
2
of the total current
3
flowing through the two resistors passes through the 12 Ω resistor? (Answer: 24 Ω)
26. What resistor should be connected in parallel with a 12 Ω resistor so that
27. A 10 Ω, 5.0 Ω and an R Ω resistor are connected
in parallel across a 20 V source. The three
€
resistors draw a total of 11 A from the source. What is the value€of R? (Answer: 4.0 Ω)
€
€
28. Solve the network.
€
€
€
€
€
I= 7.5 A
V
RΩ
€
40 Ω
2.5 A
€
Answer:
I= 7.5 A
100 V
20 Ω
5.0 A
100 V
€
€
€
100 V
40 Ω
2.5 A
€
€
29. Solve the network.
I= 6.0 A
V
8.0 Ω
€
24 Ω
€
Answer:
I= 6.0 A
8.0 Ω
36 V
4.5 A
36 V
€
€
24 Ω
36 V
1.5 A
30. Find the equivalent resistance of each combination.
(a)
6.0 Ω
€
6.0 Ω
2.0 Ω
€
(Answer: 7.5 Ω)
(b)
€5.0 Ω
2.0 Ω
€
€
1.0 Ω
€
€
12 Ω
7.0 Ω
5.0 Ω
€
(c)
€
(Answer: 6.0 Ω )
€
10 Ω
€
€
€
20 Ω
15 Ω
€
25 Ω
12 Ω
(Answer: 8.0 Ω)
€
€
€
€
3.0 Ω
(d)
4.0 Ω
40 Ω
5.0 Ω
€
€
12 Ω
€
24 Ω
€
(Answer: 23 Ω)
8.0 Ω
€
(e)
€
€
6.0 Ω
€
9.0 Ω
(Answer: 14 Ω)
€
€
10 Ω
€
31. Consider the following circuit diagram.
18 V
A
3.0 Ω
€
X
7.0 Ω
Y
Z
6.0 Ω
€
(a) What is the resistance of the parallel combination of resistors between points Y and Z?
(Answer: 2.0 Ω)
€
(b) What is the resistance of the circuit between
points X and Z? (Answer: 9.0 Ω)
(c) Assuming that the battery has negligible internal resistance, what reading would you expect
on the ammeter? (Answer: 2.0 A)
(d) €
What is the potential difference between points X and Y? (Answer: 14 V)
(e) What current flows through the 3.0 Ω resistor? (Answer: 1.3€A)
€
32. Solve the network.
20 Ω
9.0 Ω
€
60 Ω
€
€
4.0 Ω
2100 V
3.0 Ω
R 2 = 12 Ω
€
R1 = 12 Ω
€
€
€
40 Ω
€
25 Ω
Resistor
9.0 Ω €
€
€
€
€
€
€
€
€
€
€
20 Ω
60 Ω
3.0 Ω
4.0 Ω
R1 = 12 Ω
R 2 = 12 Ω
40 Ω
25 Ω
5.0 Ω
Potential Drop
€
5.0 Ω
Current
Answer:
€
€
€
€
€
Resistor
Potential Drop
Current
9.0 Ω
540 V
900 V
60 A
45 A
15 A
20 Ω
60 Ω
3.0 Ω
4.0 Ω €
R1 = 12 Ω€
R 2 = 12 Ω
40 Ω
25 Ω
5.0 Ω
€
€
900 V
180 V
€
60 A
24 A
8.0 A
380 V or 384 V€
480 V
40 0 V
32 A
12 A
16 A
16 A
96 V
96 V
80 V
€
€
€
33. Three voltmeters V, V1 and V 2 are connected as shown in the following circuit diagram.
€
€
€
€
A
L1
€
L2
€
V2
V1
€
V€
(a) If voltmeter V reads 18 V and voltmeter V1 reads 12 V then what does voltmeter V 2 read?
(Answer: 6.0 V)
(b) If the ammeter A reads .50 A then how much electrical energy is changed into heat and light
in lamp L 1 in one minute? (Answer: 360 J)
€
€
€
34. What is the power rating of an electric heater that draws 12 A when connected to a 120 V
source? (Answer: 1400 W)
35. What is the power rating of a 25 Ω iron that draws 3.2 A while operating? (Answer: 260 W)
36. The potential drop across a 30 Ω electric heater is 110 V. What is the power rating of the
heater? (Answer: 40 0 W )
€
37. How much power is dissipated (converted to heat) by the 2.0 Ω resistor?
€
€
3.0 Ω
€
€
20 V
2.0 Ω
€
€
5.0 Ω
V2
Note: The answer is not P =
=
R
€
(20 )2
2.0
= 200 W
(Answer: 8.0 W)
38. An electric hot €
plate draws 9.5 A when plugged into a 120 V source.
(a) What is the resistance of the hot plate? (Answer: 13 Ω)
(b) How much energy does the hot plate consume in 15 minutes? (Answer: 1.0 x 10 6 J)
39. A 4500 W air conditioner is connected to a 120 V source.
€ draw? (Answer: 38 A)
(a) How much current does the air conditioner
(b) What is the resistance of the air conditioner? (Answer: 3.2 Ω)€
(c) How much energy does the air conditioner use in 2.4 hours? (Answer: 3.9 x 107 J)
40. Convert 7.6 x 107 J into kWh. (Answer: 21 kWh)
€
€
41. A motor connected to a 220 V source draws 5.6 A of current. If electric
energy costs
8.0 ¢ per kWh then how much would it cost to run the motor for 12 hours?
€(Answer: $1.18)
42. (a) A kilowatt is a unit of _____. (Answer: power)
(b) A kilowatt-hour is a unit of _____. (Answer: energy)
HOMEWORK
GUIDE
Section in the
Notes
Worksheet Problems
17.1
1 to 3
17.2
4 and 5
17.3
6 to 10
17.7
11 and 12
17.8
13 to 20
17.9
21 to 29
17.10
30 to 32
18.4
33 to 39
18.6
40 to 42