TIME
OF
COMPLETION_______________
NAME__SOLUTION___________________________
DEPARTMENT OF NATURAL SCIENCES
PHYS 1112, Exam 1
Version 2
Total Weight: 100 points
Section 1
February 14, 2013
1.
Check your examination for completeness prior to starting. There are a total of ten (10)
problems on seven (7) pages.
2.
Authorized references include your calculator with calculator handbook, and the
Reference Data Pamphlet (provided by your instructor).
3.
You will have 75 minutes to complete the examination.
4.
The total weight of the examination is 100 points.
5.
There are six (6) multiple choice and four (4) calculation problems. Work five (5)
multiple choice and four (4) calculation problems. Show all work; partial credit will be given for
correct work shown.
6.
If you have any questions during the examination, see your instructor who will
be located in the classroom.
7.
Start:
Stop:
12:45 p.m.
2:00 p. m.
PROBLEM
POINTS
1-6
25
7
15
8
20
9
15
10
25
PERCENTAGE
CREDIT
CIRCLE THE SINGLE BEST ANSWER FOR ALL MULTIPLE CHOICE QUESTIONS. IN
MULTIPLE CHOICE QUESTIONS WHICH REQUIRE A CALCULATION SHOW WORK
FOR PARTIAL CREDIT.
1. When two charged conductors are connected to each other by a conducting wire, the one
that loses electrons or, equivalently, gains positive charge is said, in comparison with the
other conductor, to have had
a. A greater electric potential energy.
b. A lower capacitance.
(5)
c. A lower dielectric constant.
d. A lower potential.
2.
It takes 50.0 J of energy to move 10.0 C of charge from point A to point B. What is the
magnitude of the potential difference between points A and B?
a. 500 V.
b. 50.0 V.
(5)
c. 5.00 V.
d. 0.500 V.
3. Two point charges attract each other with an electric force of magnitude F. If one charge
is reduced to one-third its original value and the distance between the charges is
unchanged, what is the resulting magnitude of the electric force between them?
a. F/3.
b. 3F/4.
(5)
c. F/6.
d.
F/12.
e. 3F/2
4. Rank the magnitudes of the electric field at points A, B, and C shown in the figure below
(greatest magnitude first).
a. A > C > B
b. B > C > A
(5)
c. C > A > B
d. C > B > A
e.
A>B>C
5. Two capacitors are identical. They can be connected in series or in parallel. If you want
the greatest equivalent capacitance for the combination, how do you connect them?
a.
In series.
(5)
b. In parallel.
c. Either way; the combinations have the same capacitance.
6. When the potential difference across a certain conductor is doubled, the current is
observed to increase by a factor of two. What can you conclude about the conductor?
a. It obeys Ohm's Law.
b. It does not obey Ohm's Law.
(5)
c. It is a semiconductor.
d. It is a perfect conductor.
PHYS 2211 Exam 1, Version 2
Spring 2013
3
7. Two equal positively charged particles are at opposite corners of a trapezoid as shown in the
figure below. Let Q=1.50 C and d = 0.300 m.( Note that lengths of the right and left sides of
the trapezoid are equal to d / 2 .)
a. Find the electric potential at point P.
VP  ke
Q
Q
 ke
 1.09  105V
d
d/ 2
b. Find the electric potential at point P’.
VP '  ke
Q
Q
 ke
 8.60  104V
2d
d/ 2
c. How much work is required to move a 2.00 C of charge from point P to point P’?
W  qV  (2.00  106 C )(8.60  104V  1.09  105V )  0.0450 J
8. Determine the electric field at the origin 0 due to the two charges at A and B.
Specify magnitude and direction. Let Q = 1.50 C and l = 0.400 m.
PHYS 2211 Exam 1, Version 2
Spring 2013
4
E A  ke
Q
 8.43  104 N / C
2
l
@ -90o
EB  ke
Q
 8.43  104 N / C
2
l
@ 210o
E Ax  0
E Ay  8.43  104 N / C
E Bx  7.30  104 N / C
E By  4.21  104 N / C
ETOTx  E Ax  EBx  7.30  104 N / C
ETOTy  E Ay  EBy  1.26  105 N / C
ETOT  ETOTx  ETOTy  1.46  105 N / C
2
2
  240o
9. A 100-W lightbulb has a resistance of about 12  when cold (20°C) and 140  when on (hot).
Estimate the temperature of the filament when hot assuming an average temperature coefficient
1
of resistivity   0.0060 (Cº ) .
PHYS 2211 Exam 1, Version 2
Spring 2013
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R  R0 [1   (T  T0 )]
R / R0  1   (T  T0 )
[ R / R0  1] /   T0  T
T = 1798o
10. Five identical 5.00 F capacitors are connected as shown below.
a. Find equivalent capacitance of the network.
C12  C1  C2  10.0 F
1
C12345

1
1
1
1
7




C12 C3 C4 C5 10 F
C12345=10/7 F = 1.429F
b. If a potential difference of 10.0 V is applied between points a and b, how much charge is
stored on Capacitor 5?
PHYS 2211 Exam 1, Version 2
Spring 2013
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Q12  Q3  Q4  Q5  Q12345  C12345V12345  14.3 C
c. What is the potential difference across the Capacitor 2?
V2  V1  V12 
Q12 14.3 C

 1.43 V
C12 10.0 F
PHYS 2211 Exam 1, Version 2
Spring 2013
7