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DEPARTMENT OF NATURAL SCIENCES
PHYS 1112, Exam 1
Version 1
Total Weight: 100 points
Section 1
September 20, 2013
1.
Check your examination for completeness prior to starting. There are a total of nine (9)
problems on six (6) pages.
2.
Authorized references include your calculator with calculator handbook, and the
Reference Data Pamphlet (provided by your instructor).
3.
You will have 50 minutes to complete the examination.
4.
The total weight of the examination is 100 points.
5.
There are six (6) multiple choice and three (3) calculation problems. Work five (5)
multiple choice and three (3) 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:
9:00 a.m.
9:50 a. m.
PROBLEM
POINTS
1-6
25
7
25
8
25
9
25
TOTAL
100
PERCENTAGE
CREDIT
CIRCLE THE SINGLE BEST ANSWER FOR ALL MULTIPLE CHOICE QUESTIONS
UNLESS INSTRUCTED OTHERWISE. IN MULTIPLE CHOICE QUESTIONS WHICH
REQUIRE A CALCULATION SHOW WORK FOR PARTIAL CREDIT.
1. Which statements are true for a proton moving in the direction of an electric field? (There
may be more than one correct choice.) Choose all that apply.
a. Its kinetic energy decreases as it moves in the direction of the electric field.
b. Its kinetic energy increases as it moves in the direction of the electric field.
c. Its electric potential energy decreases as it goes from high to low potential.
d. Its electric potential energy increases as it goes from high to low potential.
2. When two or more capacitors are connected in parallel across a potential difference
a. Each capacitor carries the same amount of charge.
b. The potential difference across each capacitor is the same.
c. The equivalent capacitance of the combination is less than the capacitance of
any of the capacitors.
d. None of the above choices are correct.
3. You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads
to it in order to make a resistor. If you want to achieve the SMALLEST possible
resistance, you should attach the leads to the opposite faces that measure
a. 5 cm × 8 cm.
b. 3 cm × 5 cm.
c. 3 cm × 8 cm.
d. Any pair of faces produces the same resistance.
4. If the voltage across a circuit of constant resistance is doubled, how is the current in the
circuit affected?
a.
The current is quadrupled.
b. The current is reduced by a factor of 2.
c. The current remains constant.
d. The current is doubled.
5. Which of the following statements is FALSE?
a. The capacitance of a capacitor depends upon its geometry.
b. A capacitor is a device that stores electric potential energy and electric charge.
c. The electric field between the plates of a parallel-plate capacitor is uniform.
d. A capacitor consists of a single sheet of a conducting material placed in contact
with an insulating material.
6. 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
7. The average bulk resistivity of the human body (apart from surface resistance of the skin)
is about 5.0 Ω⋅m. The conducting path between the hands can be represented
approximately as a cylinder 1.6m long and 0.10 m in diameter. The skin resistance can be
made negligible by soaking the hands in salt water.
a. What is the resistance between the hands if the skin resistance is negligible?
PHYS 1112 Exam 1, Version 1
Fall 2013
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R
(1.60 m)
l
 (5.0 m)
 1019 
A
 (0.0500 m) 2
b. What potential difference between the hands is needed for a lethal shock current of
100 mA? (Note that your result shows that small potential differences produce
dangerous currents when the skin is damp.)
V  IR  101.9 V
c. With the current in part (b), what power is dissipated in the body?
P  IV  10.19 W
8. Four capacitors are connected across a 90-V voltage source as shown in the figure.
a. What is the equivalent capacitance of the combination?
1 / C12  1 / C1  1 / C 2  3 / 4 F 1
C12 = 1.33F
1 / C34  1 / C3  1 / C 4  1 / 2 F 1
C34 = 2.00F
C1234=1.33 F + 2.00F = 3.33F
PHYS 1112 Exam 1, Version 1
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b. What is the charge on the 4.0-μF capacitor?
Q2  Q12  C12 V12  120 C
c. What is the potential difference across a 2.0-μF capacitor?
V1 
Q1 120 C

 60.0 V
C1 2.00 F
9. Determine the electric field at the origin 0 due to the two charges at A and B. Specify
magnitude and direction. Let Q = 1.25 C and l = 3.50 m.
E A  ke
Q
 0.917  10 3 N / C
2
l
@ -90o
EB  ke
Q
 0.917  10 3 N / C
2
l
@ 210o
E Ax  0
E Ay  0.917  10 3 N / C
PHYS 1112 Exam 1, Version 1
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E Bx  0.794  10 3 N / C
E By  0.459  10 3 N / C
ETOTx  E Ax  E Bx  0.794  10 3 N / C
ETOTy  E Ay  E By  1.38  10 3 N / C
ETOT  ETOTx  ETOTy  1.59  10 3 N / C
2
2
  240o
PHYS 1112 Exam 1, Version 1
Fall 2013
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