Physics 9: Current Electricity
1.
A. Circuit Elements
Which is the correct way to light the light bulb with the
battery?
Name __________________________
14. What is the resistance in a 48-W light that operates at 12 V?
15. What can increase the capacitance for a parallel plate
capacitor?
2.
3.
4.
5.
6.
7.
8.
9.
Two wires, A and B, are made of the same material and
have equal lengths, but the resistance of wire A is four
times the resistance of wire B. How do their diameters
compare?
(A) DA = 4DB
(B) DA = 2DB
(C) DA = ½DB
(D) DA = ¼DB
You double the voltage across a certain conductor and you
observe the current increases three times. What can you
conclude?
(A) Ohm's law is obeyed since the current still increases
when V increases
(B) Ohm's law is not obeyed
(C) This has nothing to do with Ohm's law
A wire of resistance R is stretched uniformly (keeping its
volume constant) until it is twice its original length. What
happens to the resistance?
(A) ¼R
(B) ½R
(C) 2R
(D) 4R
When you rotate the knob of a light dimmer, what is being
changed in the electric circuit?
(A) power (B) current (C) voltage (D) both P and I
Two light bulbs operate at 120 V, but one has a power
rating of 25 W while the other has a power rating of 100 W.
Which one has the greater resistance?
(A) 25 W bulb (B) 120 W bulb (C) tie
Two space heaters are operated at 120 V. Heater A has
twice the resistance as heater B. Which one will give off
more heat?
(A) A
(B) B
(C) tie
Which current flows from high to low voltage, electron flow
or conventional current?
How many electrons (qe = -1.60 x 10-19 C) pass when a
current of 10 A runs for 25 minutes?
10. What is the current through a 200- resistor if the voltage
between its terminals is 15 V?
11. What is the internal resistance of a battery where E = 1.5 V
and the terminal voltage = 1.35 V when the current is 3 A?
16. A parallel plate capacitor consists of two metal plates
separated by 0.006 m and is connected to a 100-V source.
The area of each plate is 0.04 m2. Determine the
a. capacitance.
b.
charge on each plate.
c.
energy stored.
d.
electric field.
17. Show how a battery, bulb and two wires must be arranged
in order for the bulb to light. Use circuit element symbols.
18. A starter motor draws a current of 50 A through a cable for
5 s. Determine the number of
a. coulombs of charge which pass through the cable.
b.
electrons that pass through the cable.
19. A 50-m long wire with cross section of 3 x 10-6 m2 has a
resistance of 0.5 . What is the resistivity?
20. What is the resistance in a light bulb that draws 500 mA
current at 3 V.
21. A 10- resistor is connected to a 120 V line. Determine
a. the current through the resistor.
b.
the power dissipated in the resistor.
12. In general, how is resistivity affected by changes in
temperature?
22. What is the power rating of a theater light in which a
current of 10 A is caused by 120 V?
13. a.
Determine the electrical resistance of tungsten wire
( = 5.0 x 10-8 •m, L = 20 m and A = 1.0 x 10-6 m2).
b.
Determine the electrical resistance in the same piece
of tungsten after it is stretched to a length of 60 m.
B. Series and Parallel Circuit Design
23. A 9-V battery is connected to three identical resistors in
series. What is the voltage across each resistor?
(A) 3 V
(B) 9 V
(C) 18 V
(D) 27 V
Questions 24-25 A battery of voltage V is connected to a 4-
and 2- resistor in series.
24. What is the same for both resistors?
(A) P
(B) I
(C) V
(D) both P and I
25. What is the voltage across the 4- resistor?
(A) 1/3V
(B) 1/2 V
(C) 2/3 V
(D) V
Questions 26-27 Current, I, enters a parallel circuit containing a
2- resistor and a 4- resistor.
26. What is the same for both resistors?
(A) P
(B) I
(C) V
(D) both P and I
27. What is the current through the 4- resistor?
(A) 1/3 I
(B) ½ I
(C) 2/3 I
(D) I
Questions 28-29 Two light bulbs (resistors) are in series, with a
wire and switch connected parallel to one of the bulbs.
Compared to when the switch is open, how does the bulb's
brightness change when the switch is closed?
b.
c.
(Current or Voltage) is the same for resistors in parallel.
You can disconnect one device without stopping the
current in a (series or parallel) circuit.
d. Two light bulbs arranged in (series or parallel) will
generate the most light.
43. 3- and 6- resistors in series connected to 6 V.
Total R
Total I
Total P
V for 3 
A
B
V for 6 
28. Bulb A?
(A) dimmer (B) same
(C) brighter (D) no light
P for 3 
29. Bulb B?
(A) dimmer (B) same
(C) brighter (D) no light
P for 6 
Questions 30-31 Two light bulbs are in series with a 12-V battery.
30. What happens to the total brightness when one light bulb is
removed?
44. 3- and 6- resistors in parallel connected to 6 V.
(A) dimmer (B) same
(C) brighter (D) no light
Total R
31. What happens to the total brightness when one light bulb is
replaced by a wire?
(A) dimmer (B) same
(C) brighter (D) no light
Total I
Questions 32-33 Two light bulbs are parallel with a 12-V battery.
32. What happens to the total brightness when one light bulb is
Total P
removed?
(A) dimmer (B) same
(C) brighter (D) no light
I for 3 
33. What happens to the total brightness when one light bulb is
replaced by a wire?
I for 6 
(A) dimmer (B) same
(C) brighter (D) no light
Questions 34-36 The three light bulbs have the same resistance.
P for 3 
C
A
B
P for 6 
34. The current through bulb C compared to bulb A is
45. Given R1 = 6 , R2 = 12 , and R3 = 2  are arranged in
(A) ¼
(B) ½
(C) 2
(D) 4
the following circuit. Determine the
35. The voltage drop across bulb C compared to bulb A is
(A) ¼
(B) ½
(C) 2
(D) 4
R1
36. How much brighter is bulb C compared to A?
R3
(A) ¼
(B) ½
(C) 2
(D) 4
R
12
V
2
Questions 37-39 A 6-A current is measured at point X in a circuit
containing identical 1- light bulbs A, B, C, D and E.
a. total resistance.
A
C
D
X
B
E
b. total current leaving the battery.
37. What is the correct order from greatest (1) to least (5)
current?
IA
38.
39.
40.
41.
42.
IB
IC
ID
IE
(A)
1
1
3
3
3
(B)
2
2
4
4
1
(C)
4
4
2
2
1
(D)
2
2
1
1
4
Which generates the most light?
(A) A + B
(B) C + D
(C) E
Which has the smallest voltage drop?
(A) A
(B) C
(C) E
Two capacitors are in series with a 12-V battery. What
happens to the total capacitance when one capacitor is
replaced by a wire?
(A) decrease
(B) same
(C) increase
Two capacitors are in parallel a 12-V battery. What
happens to the total capacitance when one capacitor is
replaced by a wire?
(A) decrease
(B) same
(C) increase
Highlight the correct option for the following sentences.
a. (Current or Voltage) is the same for resistor in series.
c.
voltage drop across R3.
d.
voltage, current and power for each resistor.
V
P
I
R1
R2
R3
e.
Show that the power dissipated in the resistors equals
the power generated by the battery?
46. Highlight the correct option for the following sentences.
a. Capacitor (Charge or Voltage) is the same in series.
b. Capacitor (Charge or Voltage) is the same in parallel.
47. 3-F and 6-F capacitors in series connected to 6 V.
50. Show where a voltmeter (V) and ammeter (A) would be
placed in order to measure volts and amps in the resistor.
(A/V)
Ctot
(A/V)
Qtot
51. Three 12-resistors can be connected in four different
ways. Determine overall resistance of each combination?
UC-tot
V3
V6
52. Determine the equivalent resistance when three resistors
rated at 2-, 4-, and 6- are connected in
UC-3
UC-6
series
48. 3-F and 6-F capacitors in parallel connected to 6 V.
parallel
53. A 100-W, 120-V lamp bulb is connected in parallel with a
60-W, 120-V lamp bulb. What is their combined
resistance?
Ctot
Qtot
UC-tot
Q3
54. Consider the following circuit.
5
Q6
UC-3
49. Three capacitors, C1 = 10 F, C2 = 20 F, C3 = 30 F, are
arranged as shown below. Determine the
C1
C3
120 V
C2
a.
total capacitance.
b.
total charge stored on C3.
6
90V
1
Determine the
UC-6
a.
12 
Rtot
Itot
b. Determine current, voltage and power for each resistor.
V
P
Resistor
I
(15 F)
1
5
12 
c.
voltage across C3.
d.
voltage, charge and potential energy for each capacitor.
V
Q
UC
6
55. Consider the following circuit
⁄switch
15 
50V
C1
C2
a.
6F
10 
When the switch is open, determine
(1) charge on the 6 F capacitor.
C3
(2) energy stored in the 6 F capacitor.
b.
When the switch is closed, determine
(1) Voltage across the capacitor.
(2) charge on the 6 F capacitor.
7. A battery with an internal resistance of 4  connected
to a l6- and a 20- resistor in series. The current in the
20- resistor is 0.3 A.
(3) energy stored in the 6 F capacitor.
Practice Multiple Choice
Briefly explain why the answer is correct in the space provided.
Questions 1-2 The four resistors have the lengths, L, and
cross-sectional areas, A, indicated and are made of
material with the same resistivity.
(A) L = 1 m, A = 1 m2
(B) L = 2 m, A = 1 m2
(C) L = 1 m, A = 2 m2
(D) L = 2 m, A = 2 m2
1. Which resistor has the least resistance?
What is the emf, E, of the battery?
(A) 1.2 V
(B) 6.0 V
(C) 10.8 V
8.
2.
Which has the greatest resistance?
3.
A circuit consists of a 10- resistor, a 15- resistor, and a
20- resistor connected in parallel across a 9-V battery.
What is the equivalent resistance of this circuit?
(A) 0.2 
(B) 2 
(C) 4.6 
(D) 45 
4.
A lamp, a voltmeter V, an ammeter A, and a battery with
zero internal resistance are connected as shown.
How would the addition of a second lamp affect the
ammeter and voltmeter readings?
A
V
A
V
(A) increase same
(B) decrease decrease
(C) same
increase (D) decrease decrease
Two 4.0- resistors are connected to a I6-V battery.
9.
The power generated in the circuit is
(A) 8 W
(B) 16 W
(C) 32 W
(D) 12 V
An electric circuit contains a variable resistor connected to
a battery. Which graph best represents the relationship
between current and resistance in this circuit?
(A)
(B)
(C)
(D)
(D) 64 W
Questions 5-6 relate to the four incomplete circuits below
composed of resistors R, all of equal resistance, and
capacitors C, all of equal capacitance. A battery that can
be used to complete any of the circuits is available.
R
R
C
R
(A)
(B)
Questions 10-12 refer to the circuit shown below.
d
.
C
(C)
R
d
.
R
(D)
R
R
5.
Into which circuit should the battery be connected to obtain
the greatest steady power dissipation?
6.
Which circuit will retain stored energy if the battery is
connected to it and then disconnected?
10. The equivalent capacitance for this network is
(A) 10/7 F (B) 3/2 F
(C) 7/3 F
(D) 7 F
11. The charge stored in the 5-F capacitor is
(A) 360 C (B) 500 C (C) 710 C (D) 1,100 C
12. The electrical energy stored in the 5-F capacitor is
(A) 0.025 J (B) 0.050 J (C) 2.5 J
(D) 500 J
Questions 13-14 refer to partial electric circuit.
20. What is the value of r?
(A) 0 
13. The electrical resistance between point X and point Y is
(A) 4/3 
(B) 2 
(C) 11/4 
(D) 4 
(B) 1 
(C) 5 
(D) 20 
Questions 21-22 refer to the circuit shown below.
14. The current is
(A) the same everywhere in the circuit
(B) greater at point X than at point Y
(C) greater in the 1  resistor than in the 2  resistor
(D) greater in the 2  resistor than in the 3  resistor
15. A 10- heater is used to heat water. If the heater draws 3
A for 100 s, how much energy is transferred to the water?
(A) 30
(B) 300
(C) 3,000 (D) 9,000
Questions 16-18 The circuit consisting of four resistors and a
12-V battery.
21. What is the current I1?
(A) 0.8 mA (B) 1.0 mA (C) 2.0 mA (D) 3.0 mA
22. How do the currents I1, I2, and I3 compare?
(A) I1 > I2 > I3
(B) I1 > I3 > I2
(C) I2 > I1 > I3
(D) I3 > I1 > I2
16. What is the current measured by the ammeter?
(A) 0.5 A
(B) 2 A
(C) 72 A
(D) 4 A
17. What is the equivalent resistance of this circuit?
(A) 72 
(B) 3 
(C) 18 
(D) 0.33 
18. How much power is dissipated in the 36- resistor?
(A) 110 W (B) 3 W
(C) 48 W
(D) 4 W
23. What percentage of the power generated by a 0.5 A, 120 V
electric motor is used to lift a 9 kg mass against gravity at
an average velocity of 0.5 m/s?
(A) 7%
(B) 13%
(C) 25%
(D) 75%
24. A wire of length L and radius r has a resistance R. What is
the resistance of a second wire made from the same
material that has a length ½L and a radius ½r?
(A) 4R
(B) 2R
(C) R
(D) ½R
19. What is the voltage between points X and Y?
Practice Free Response
1.
Consider the following circuit.
C1
C2

R3
R4
R2
R1
(A) 1 V
(B) 2 V
(C) 3 V
(D) 4 V
R5
9V
a.
C3
Determine the following values.
R3 + R4
R3-4 + R5
Rtot
R6
Itot
V5
I5
I3
C1 + C2
Q1+2
V1
V2
Q3
b. Complete the table for each resistor and capacitor.
R
V
P
Resistor
I
Overall
___ 
R1
1
R2
3
R3
3
R4
3
R5
3
R6
3
Capacitor
C
C1
30 F
C2
15 F
C3
20 F
Q
V
Uc