PHYS 212 – MT2 Summer 2012 Sample 3

PHYS 212 – MT2
Summer 2012
Sample 3
Question 1
Two charges lie on the x-axis. A representation of the equipotentials of the electric potential of
these two charges is shown below. The "streaks" in this representation are parallel to the
equipotential curves
Which one of the following statements about the sign and magnitude of the charges is true?
Compared to the right charge, the left charge…
A.
B.
C.
D.
E.
has the opposite sign and is smaller in magnitude.
has the opposite sign and is larger in magnitude.
has the same sign and is smaller in magnitude.
has the same sign and is larger in magnitude.
has the same sign and the same magnitude.
Page 1 of 10
PHYS 212 – MT2
Summer 2012
Sample 3
Question 2
In the figure, what should be the position of the switches for the potential across R to be zero?
A.
B.
C.
D.
E.
S1 open, S2 closed.
Both open.
S2 open, S1 closed.
Both closed.
More than one answer above is right.
Question 3
In the diagram R1 > R2 > R3. Rank the three resistors according to the voltage across them, least
to greatest.
A. All are the same
B. V3 < V1 < V2
C. V3 < V2 < V1
D. V1 < V3 < V2
E. V1 < V2 < V3
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PHYS 212 – MT2
Summer 2012
Sample 3
Question 4
Consider the circuit drawn below. Given the way the currents are labeled, which of the following
equations is correct? Start from point a and proceed clockwise around the outer loop
A.  I1R1  I 2 R2   2  1  0
B. I1R1  I 2 R2   2  1  0
C.  I1R1  I 2 R2   2  1  0
D.  I1R1  I 2 R2   2  1  0
E.  I1R1  I 2 R2   2  1  0
Question 5
Positive charge is distributed uniformly throughout a solid non-conducting sphere. The highest
electric potential occurs:
A.
B.
C.
D.
E.
at the center
at the surface
halfway between the center and surface
just outside the surface
far from the sphere
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PHYS 212 – MT2
Summer 2012
Sample 3
The next three questions refer to the figure at right, which
shows some equipotential lines in a region of space.
Question 6
A proton is released from rest at point A. In which direction
will it initially start moving?
A. Up
B. Down
C. Right
D. The proton will drift along the 0 V contour line, in
either direction
E. The proton will remain at rest
Question 7
At which of the three labeled points (A, B, C) is the electric field the strongest?
A. At the point A
B. At the point B
C. At the point C
D. It is equally strong at points A and B (but is stronger at both of those than at point C)
E. It is equally strong at points B and C (but is stronger at both of those than at point A)
Question 8
Now consider moving a proton from point B to point C with constant velocity. How much
external work would this take (i.e. how much work would you need to do)?
A. -3 eV
B. +3 eV
C. -6 eV
D. +6 eV
E. -1.6 ⋅10-19 eV
F. +1.6 ⋅10-19 eV
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PHYS 212 – MT2
Summer 2012
Question 9
A parallel plate capacitor has a charge-potential differential
relationship as plotted in the solid line at right. It is connected to a
battery and charged so that its state is indicated by the big blue dot.
With the battery still connected, you do positive work on the plates of
the capacitor in order to modify its charge-potential difference
relationship to one of the two dashed lines. At which, if any, of the 4
labeled states does the capacitor end up?
A.
B.
C.
D.
E.
Sample 3
q
B
A
D
C
V
A
B
C
D
None of the above
Question 10
Two points, A and B, are in a uniform electric field which points
up the page, as shown, with magnitude 15 N/C.
Point A is located at the origin (x,y) = (0 m, 0 m)
Point B is located at (x,y) = (3 m, 4 m)
The zero of voltage has been chosen to lie at point A.
What is the voltage at point B?
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
+15 V
-15 V
+45 V
-45 V
+60 V
-60 V
+75 V
-75 V
Impossible to determine given the above information
None of the above
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PHYS 212 – MT2
Summer 2012
Sample 3
The following two questions use the same set-up
A positive charge q sits on the top vertex of an
equilateral triangle, with two unknown charges
q2 and q3 on the other two vertices. The point P
is at the center of the triangle and is a distance a
from each of the charges (see sketch) and a
distance a/2 up from the base of the triangle. If
we define the electric potential at infinity to be
zero, we find that the electric potential at point
P is also zero. Moreover, we find that the
electric field at point P points purely along the
y-axis.
Question 11
What is the charge q2?
A. q
B. –q
C. 2q
D. -2q
E. q/2
F. –q/2
G. Cannot determine from the given information
H. None of the above
Question 12
How much work would you need to do to bring a positive charge Q from infinity to the origin
(midway between the charges q2 and q3)?
A. 2kqQ
3a
B.  2kqQ
3a
3kqQ
C.
a
3kqQ
D. 
a
E. 0
F. None of the above
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PHYS 212 – MT2
Summer 2012
Sample 3
The next four questions all depend on the following setup.
A
C
V = 10 V
12
10
(0.1 s, 9.0 V)
8
11
6
I1 (mA)
Voltage across elementB (volts)
The circuit at right consists of a 10 V battery, a switch S, and
three other circuit components (either resistors or capacitors),
hidden in boxes labeled A, B & C. You are given the circuit,
in which the switch has been open for a very long time, and
asked to determine what is in the boxes. You close the switch
and record the voltage across element B and the current I1
through element C. You also tried to record the current I2
through A & B, but unfortunately only got its value the instant
the switch was closed, which was I2(t=0+) = 10 mA. VB and I1
are plotted below:
B
(0.7 s, 5.0 V)
4
(1.0 s, 10 mA)
10
(10.0 s, 10 mA)
(1.1 s, 3.3 V)
9
2
8
0
0
2
4
6
Time (seconds)
8
10
0
2
4
6
8
10
Time (seconds)
Question 13
What circuit element is in box C, and what is its numerical value (i.e. resistance if a resistor,
capacitance if a capacitor)?
A.
B.
C.
D.
E.
F.
G.
1
10 
1 k
1 mF
10 mF
100 mF
None of the above
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PHYS 212 – MT2
B
C
V = 10 V
Voltage across elementB (volts)
A
Summer 2012
Sample 3
10
(0.1 s, 9.0 V)
8
6
(0.7 s, 5.0 V)
4
(1.1 s, 3.3 V)
2
0
0
2
4
6
8
10
Time (seconds)
Question 14
What circuit element is in box B, and what is its numerical value (i.e. resistance if a resistor,
capacitance if a capacitor)?
A.
B.
C.
D.
E.
F.
G.
1
10 
1 k
1 mF
10 mF
100 mF
None of the above
Question 15
What is the approximate time constant of the voltage decay across element B?
A. 0.1 s
B. 0.6 s
C. 0.7 s
D. 1.0 s
E. 1.1 s
F. 2.0 s
Question 16
What circuit element is in box A, and what is its numerical value (i.e. resistance if a resistor,
capacitance if a capacitor)?
A.
B.
C.
D.
E.
F.
G.
1
10 
1 k
1 mF
10 mF
100 mF
None of the above
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PHYS 212 – MT2
Summer 2012
Sample 3
Question 17
The circuit at left consists of three identical
resistors each with resistance R, two
identical batteries with emfs , and a
capacitor with capacitance C. The capacitor
is initially uncharged at t = 0. After a very
long time, what is the charge Q (as labeled
in the picture) on the capacitor?
A.
B.
C.
D.
E.
F.
G.
Q  23 C
Q  C
Q  12 C
Q0
Q   12 C
Q  C
Q   23 C
Question 18
A parallel plate capacitor is charged using a battery and the battery is then removed. The plates
of the capacitor are now brought closer together. Which of the following statements is FALSE?
A. The electric field inside the capacitor remains the same.
B. The potential difference between the plates of the capacitor decreases.
C. The capacitance of the capacitor increases.
D. The charge on the capacitor remains the same.
E. The energy stored in the capacitor increases.
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PHYS 212 – MT2
Summer 2012
Sample 3
Question 19
A 12 V car battery connected to 10  resistor supplies 1 A of current. What is the maximum
current that the battery can supply?
A.
B.
C.
D.
E.
F.
1 A
1.2 A
2 A
Theoretically it could supply any amount of current
There isn’t enough information provided to determine the maximum (but there is one)
None of the above
Question 20
Two uncharged conductors, A and B, are of different sizes. They are charged as follows:
1. A is charged from an electrostatic generator to charge q.
2. A is briefly touched to B.
3. Steps 1 and 2 are repeated until the charge on B reaches a maximum value.
After the first touch the electrostatic energy associated with B is four times that of A (when they
are well isolated from each other). After the process is complete (after B has been charged as
completely as possible) how much charge is on B?
A.
B.
C.
D.
E.
F.
q/4
q/2
q
2q
4q
None of the above
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