Mark Reeves - Physics 22, Fall 2011
Pract2a
1
4 pt
A point charge of mass 0.0699 kg and charge q = +6.87 µC
is suspended by a thread between the vertical parallel plates
of a parallel-plate capacitor, as shown in the figure below.
4 pt
An electron beam is deflected upward through 3.22 mm while
traveling in a vacuum between two deflection plates 12.0 mm
apart (the figure below ). The potential difference between
the deflecting plates is 123 kV and the kinetic energy of each
electron as it enters the space between the plates is 1.69 ×
10−15 J. What is the kinetic energy of each electron when it
leaves the space between the plates?
d
+
Electron beam
q
Deflection
_
(in J)
q
3.A 4.84 × 10−15 B 5.46 × 10−15
C 6.17 × 10−15 D 6.98 × 10−15
E 7.88 × 10−15
If the angle of deflection is θ = 24.6◦, and the separation
between the plates is d = 0.0229 m, what is the potential
difference between the plates?
(in V)
1.A 3.34 × 102
D 7.87 × 102
B 4.45 × 102
E 1.05 × 103
C 5.92 × 102
4 pt
Two identical conducting spheres carry charges of +6.04 µC
and -1.44 µC respectively. They are initially a large distance
L apart. The spheres are brought together, touched together,
and then returned to their original separation L. What is the
ratio of the magnitude of the force on either sphere after they
are touched to that before they were touched?
2.A 2.89 × 10−1 B 4.19 × 10−1 C 6.08 × 10−1
D 8.82 × 10−1 E 1.28
4 pt
Find the electric potential energy for the following array of
charges:
charge q1 = +4.08 µC is located at (x, y) = (0.0, 0.0) m;
charge q2 = +3.17 µC is located at (3.92, 3.07) m;
and charge q3 = -1.05 µC is located at (0.0, 3.07) m.
(in J)
4.A 2.19 × 10−3 B 3.17 × 10−3 C 4.60 × 10−3
D 6.67 × 10−3 E 9.67 × 10−3
Two uniformely charged spheres are suspended by strings of
length L from vertically adjustable supports. The spheres
are in static equilibrium and at the same height, as shown
below.
Q
W
T
Z
Mark Reeves - Physics 22, Fall 2011
Pract2a
3
4 pt Which statements regarding a plate capacitor are true?
4 pt The angles with respect to the vertical are Q=11.1◦ ,
and T=21.3◦ .
⊲ The amount of charge on Z can be equal to that on W.
5. A True B False C Cannot tell
⊲ The charge on W can be positive and that on Z negative.
6. A True B False C Cannot tell
⊲ The amount of charge on Z can be greater than that on W.
7. A True B False C Cannot tell
⊲ The charge on W can be positive and that on Z positive.
8. A True B False C Cannot tell
⊲ The mass of W can be less than that of Z.
9. A True B False C Cannot tell
⊲ The charge of a disconnected charged plate capacitor increases when the plates are pulled apart
14. A True B False
⊲ The capacitance is proportional to the area
15. A True B False
⊲ The capacitance is proportional to the gap width
16. A True B False
⊲ The voltage across a disconnected charged plate capacitor
increases when the plates are pulled apart
17. A True B False
⊲ The capacitance depends on the material between the
plates.
18. A True B False
A capacitor is completely charged with 680 nC by a voltage
source that had 225 V.
4 pt The tension in the string supporting sphere W is 2.75E5 N. Calculate the tension in the other string.
(in N)
10.A 5.97 × 10−6 B 7.46 × 10−6 C 9.33 × 10−6
D 1.17 × 10−5 E 1.46 × 10−5
4 pt What is its capacitance? (in F)
19.A 2.21 × 10−9 B 2.58 × 10−9 C 3.02 × 10−9
D 3.54 × 10−9 E 4.14 × 10−9
4 pt Three arrangements of capacitors with capacities
indicated (in µF) are shown in the figure below.
43
66
7.0
9.4
8.2
66
23
28
66
Rank their equivalent capacitances in order of INCREASING
value. (smallest has rank 1)
4 pt Now the plates of the charged capacitor are pushed together with the voltage source already disconnected.
20. A The energy stored in the capacitor remains the
same.
B The capacitance increases.
C The charge on the plates increases.
D The voltage drop between the plates increases.
E None of the above.
⊲ Capacitance of configuration X.
11. A Rank 1 B Rank 2 C Rank 3
⊲ Capacitance of configuration Y.
12. A Rank 1 B Rank 2 C Rank 3
⊲ Capacitance of configuration Z.
13. A Rank 1 B Rank 2 C Rank 3
4 pt The initial air gap of the capacitor above was 8 mm.
What is the stored energy if the air gap is now 2 mm? (in J)
B 1.91 × 10−5 C 1.38 × 10−4
21.A 0.00
D 3.06 × 10−4 E 3.63 × 10−4
Mark Reeves - Physics 22, Fall 2011
Pract2a
5
The figure shows the equipotential lines of a charge distribution and labelled locations.
D
C
B
A
A 5-year old has nothing better
to do than to connect three capacitors to a voltage source
as shown. The capacitors have C1=58 mF, C2=70 mF, and
C3=18 mF, respectively, and the voltage source has 4 Volts.
4 pt What is the total capacitance? (in mF)
22.A 26.5
E 49.7
B 31.0
C 36.3
D 42.5
4 pt What is the total energy stored in the capacitors? (in
mJ)
23.A 398 B 465 C 544 D 637 E 745
E
4 pt
Where do you expect the strongest electric field?
26. A A
B B
C C
D D
E E
4 pt What is the direction of the electric field at A?
27. A Approximately parallel to the x-axis.
B Approximately parallel to the y-axis.
C No field.
Q
P
+
O
-
R
S
Two charges of equal magnitude are located on the horizontal
axis at equal distances from the vertical axis.
4 pt What is the direction of the electric field at E?
28. A Approximately parallel to the x-axis.
B Approximately parallel to the y-axis.
C No field.
4 pt At what location does the electric field point due west?
24. A P
B S
C O
D None of the locations
The following figure shows the electric field lines of two point
charges:
A
D
4 pt Where does the electric field point at location R?
25. A West
B South
C East
D North
E No field
C
B
Mark Reeves - Physics 22, Fall 2011
Pract2a
7
4 pt
Closest to which one of the locations would you expect no
electric field?
29. A A
B B
C C
D D
E Nowhere.
4 pt How much work by an external force does it take to
move the charge Q = 11µC from x1= 0.07 m to x2= 0.32 m?
(in J)
32.A −1.76 × 10−3 B −1.45 × 10−3 C −8.42 × 10−4
D −7.07 × 10−4 E 4.29 × 10−4
d
a
b
c
4 pt
The electric field at location A is ...
30. A ...
B ...
neither
C ...
D ...
stronger than at location C
about the same strength as at location C, and
is zero.
weaker than at location C, but not zero.
zero.
e
4 pt
Consider the arrangement of two fixed point charges, equal
in magnitude, shown in the figure. Which of the following
statements are correct for the initial motion of a third charge
if it is released from rest in the vicinity of the two charges
shown?
⊲ A negative charge at point e will accelerate up.
33. A True B False
⊲ A negative charge at point d will accelerate down.
34. A True B False
⊲ A positive charge at point c will accelerate toward the lowerleft.
35. A True B False
A constant electric field of magnitude E = 306 V/m points
in the positive x-direction. A charge Q is moved in positive
x-direction within the field by an external force.
4 pt
31. A The work required is inversely proportional to the
distance travelled.
B The work required is directly proportional to the
distance travelled.
C Without an external force, a free negative charge
would accelerate perpendicular to the depicted path.
D Without an external force, a free negative charge
would accelerate in the direction of the depicted path.
E The work required is proportional to the square of
the charge.
⊲ A positive charge at point a will accelerate toward the lowerleft.
36. A True B False
⊲ A negative charge at point b will accelerate down.
37. A True B False
Mark Reeves - Physics 22, Fall 2011
Pract2a
9
4 pt Three charges, Q1 , Q2 , and Q3 are located in a straight
line. The position of Q2 is 0.301 m to the right of Q1 . Q3 is
located 0.169 m to the right of Q2 . The force on Q2 due to
its interaction with Q3 is directed to the.....
a
b
4 pt
c
Consider two uniformly charged parallel plates as shown in
the figure. The magnitudes of the charges are equal. Select
True or False for the following statements.
⊲ Left if the two charges are positive.
38. A True B False
⊲ Left if the two charges are negative.
39. A True B False
⊲ Left if the two charges have opposite signs.
40. A True B False
⊲ Right if the two charges have opposite signs.
41. A True B False
⊲ Right if the two charges are negative.
42. A True B False
(in N)
B 1.47
C 1.67
D 1.88
4 pt Now the charges Q1= 1.90·10-6 C and Q2= -2.46·10-6
C are fixed at their positions, distance 0.301 m apart, and
the charge Q3= 3.03·10-6 C is moved along the straight line.
For what position of Q3 relative to Q1 is the net force on Q3
due to Q1 and Q2 zero? Use the plus sign for Q3 to the right
of Q1.
(in m)
44.A -1.51
E -2.47
B -1.71
C -1.93
⊲ If both plates are positively charged, there is no electric
field at b.
46. A True B False
⊲ If both plates are negatively charged, the electric field at a
points towards the top of the page
47. A True B False
4 pt In the above problem, Q1 = 1.90·10-6 C, Q2 = -2.46·10-6
C, and Q3 = 3.03·10-6 C. Calculate the total force on Q2 . Give
with the plus sign for a force directed to the right.
43.A 1.30
E 2.13
⊲ If the plates are oppositely charged, there is no electric field
at c.
45. A True B False
D -2.18
4 pt
If the plates are 1.0 cm by 1.0 cm squares, and the charges on
the plates are +/- 2.2 µC respectively, what is the magnitude
of the electric field at b? Assume that the spacing between
the plates is much less than 1 cm.
(in V/m)
48.A 1.057 × 109
C 1.869 × 109
E 3.306 × 109
B 1.405 × 109
D 2.486 × 109
4 pt Consider a sphere of radius R = 7.16 m where a charge
of Q = 12.7 µC is uniformly distributed through the volume
of the sphere. What is the magnitude of the electric field
at a point halfway between the center of the sphere and its
surface?
(in V/m)
49.A 1.11 × 103
D 3.39 × 103
B 1.61 × 103
E 4.92 × 103
C 2.34 × 103
Mark Reeves - Physics 22, Fall 2011
Pract2a
11
A solid metal sphere of radius a = 1.30 cm is surrounded by
a concentric spherical metal shell of inner radius b = 1.80 cm
and outer radius c = 2.30 cm. The inner sphere has a net
charge of Q1 = 4.10 µC, and the outer spherical shell has a
net charge of Q2 = -7.40 µC.
4 pt
Figure 1
+q
Figure 2
-q
-q
-q
L
c
a
b
c
*
a
-q
b
*
+q
+q
*
d
+q
*
Consider two separate systems, each with four charges of
magnitude q arranged in a square of length L as shown above.
Points a and c are in the center of their squares while points
b and d are half way between the lower two charges. Complete the following statements.
4 pt What is the radial component of the electric field Er at
a point located at radius r = 1.50 cm, i.e. between the two
conductors? Er is positive if it points outward, negative if it
points inward.
(in N/C)
50.A 6.96 × 107
D 1.64 × 108
B 9.26 × 107
E 2.18 × 108
C 1.23 × 108
⊲ The electric potential at a is ....
54. A Positive B Negative C Zero
⊲ The electric potential at c is ....
55. A Positive B Negative C Zero
⊲ The electric potential at d is ....
56. A Positive B Negative C Zero
4 pt What is Er at a point located at radius r = 2.70 cm,
i.e. outside the outer shell?
(in N/C)
⊲ The electric potential at b is ....
57. A Positive B Negative C Zero
51.A −1.67 × 107 B −2.08 × 107 C −2.60 × 107
D −3.26 × 107 E −4.07 × 107
Voltage (volts)
4
4 pt What is the surface charge density, σ b, on the inner
surface of the outer spherical conductor?
(in C/m^2)
0
52.A −6.18 × 10−4 B −6.98 × 10−4 C −7.89 × 10−4
D −8.91 × 10−4 E −1.01 × 10−3
-2
4 pt
4 pt What is the surface charge density, σ c, on the outer
surface of the outer spherical conductor?
(in C/m^2)
53.A −3.04 × 10−4 B −3.44 × 10−4 C −3.89 × 10−4
D −4.39 × 10−4 E −4.96 × 10−4
2
0
5
10
x (meters)
What is the electric field at the point x=6.5 m? Positive
E-fields point to the right.
(in V/m)
58.A −4.43 × 10−1 B −6.42 × 10−1 C −9.31 × 10−1
D -1.35
E -1.96
Mark Reeves - Physics 22, Fall 2011
Pract2a
13
4 pt The figure below shows identical light bulbs connected
to a battery. All the bulbs are glowing. Rank the brightness
of the bulbs, from brightest (rank 1) to dimmest (rank 5).
4 pt In the circuit below, a constant current of i = 2.37 A
flows from b to c through the 8 Ω resistor.
8
25
7
Calculate the potential difference between points a and d.
(in V)
⊲ bulb E
59. A Rank 1 B Rank 2 C Rank 3
D Rank 4 E Rank 5
65.A 1.46 × 102
D 3.43 × 102
B 1.94 × 102
E 4.57 × 102
C 2.58 × 102
⊲ bulb D
60. A Rank 1 B Rank 2 C Rank 3
D Rank 4 E Rank 5
⊲ bulb A
61. A Rank 1 B Rank 2 C Rank 3
D Rank 4 E Rank 5
4 pt Consider the circuit shown in the figure. Calculate the
potential difference across R4. Use the following data: R1 =
27.0 Ω, R2 = 18.5 Ω, R3 = 19.0 Ω, R4 = 25.5 Ω, ε = 25.0 V.
⊲ bulb B
62. A Rank 1 B Rank 2 C Rank 3
D Rank 4 E Rank 5
⊲ bulb F
63. A Rank 1 B Rank 2 C Rank 3
D Rank 4 E Rank 5
(in V)
66.A 4.71
D 9.19
B 5.88
E 1.15 × 101
C 7.35
4 pt
4 pt
In the circuit above,
the magnitudes of the currents through R1 , R2 , R3 are
I1 , I2 , I3 , respectively. Which one of the following equations
is always true?
64. A I2 = I3 · R2 /R3
B I2 = I1 · R2 /R3
C I1 = I2 = I3
D I1 ≥ I3
E I2 = I3
Calculate the current in R2.
(in A)
67.A 2.67 × 10−1 B 3.56 × 10−1 C 4.73 × 10−1
D 6.29 × 10−1 E 8.37 × 10−1
Mark Reeves - Physics 22, Fall 2011
Pract2a
15
4 pt Two batteries (V1 = 15 V and V2 = 12 V) are in a
circuit with three identical resistors (R1 = R2 = R3 = 5.7 Ω).
What is the current in the R3 resistor? Note that all resistor
values are equal, which greatly simplifies your loop equations.
68.A 2.281
E 5.568
(in A)
B 2.851
C 3.564
D 4.454
4 pt Consider the circuit shown below, with a battery and
three identical light bulbs, and a switch connecting the third
bulb to the circuit. Initially, the switch is open. Now,
we are going to close the switch. Which of the following statements are true when the switch is closed (compared to the initial state, when the switch was open)?
⊲ Bulb #3, which was initially on, now goes out completely.
69. A True B False
⊲ The total power dissipated in the circuit increases.
70. A True B False
⊲ The voltage across bulb #2 does not change.
71. A True B False
⊲ Bulb #2 gets dimmer than before, but does not go out.
72. A True B False
⊲ The current through the battery decreases.
73. A True B False
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