Download examination #1

EXAMINATION #1
Department of Physics
J. B. Bindell, PhD
PLACE YOUR ANSWERS TO THE MULTIPLE CHOICE QUESTIONS IN THIS TABLE.
Question
Multiple Choice
1
2
3
4
5
Problem #2
Problem #3
Problem #4
Student
Answer
Points
Awarded
TOTAL
NAME ____________________________________
PID
_____________________________________
Signature ___________________________________
Name ___________________________________ (print clearly on each page)
PHY-2054 College Physics II
Dr. Bindell – Section 005
EXAMINATION #1
INSTRUCTIONS: Answer all questions carefully. It is always best to use symbols
to solve problems and to then add the numbers. This makes it easier to follow your
work and easier for you to check your work if you have time. Read the questions
carefully. Draw a diagram wherever possible. Be sure to put your name at the top of each page
so that if the pages get separated during the grading process, they can all be identified. Use the
back of the page if you need more room. Constants are below. Good luck.
 k=9.0 x 109 Nm2/C2
e=1.6 x 10-19 C 
Problem #1 (4 points each = 20 points)
1. Which one of the following statements best explains why tiny bits of paper are attracted to a
charged rubber rod?
A) Paper is naturally a positive material.
B) Paper is naturally a negative material.
C) The paper becomes electrically polarized by induction.
D) Rubber and paper always attract each other.
E) The paper acquires a net positive charge by induction.
2. Two uncharged conducting spheres, A and B, are suspended from insulating threads so that
they touch each other. While a negatively charged rod is held near, but not touching sphere A,
someone moves ball B away from A. How will the spheres be charged, if at all?
Sphere A
Sphere B
A) 0
+
B) –
+
C) 0
0
D) –
0
E) +
–
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Name ___________________________________ (print clearly on each page)
3. Consider three identical metal spheres, A, B, and C. Sphere A carries a charge of –2.0 µC;
sphere B carries a charge of –6.0 µC; and sphere C carries a charge of +4.0 µC. Spheres A and
B are touched together and then separated. Spheres B and C are then touched and separated.
Does sphere C end up with an excess or a deficiency of electrons and how many electrons is it?
A) deficiency, 6 × 1013
B) excess, 3 × 1013
C) excess, 2 × 1013
D) deficiency, 3 × 1012
E) There is no excess or deficiency of electrons.
4. Four point charges are held fixed at the corners of a square as shown in the figure. Which of
the five arrows shown below most accurately shows the direction of the net force on the charge –
Q due to the presence of the three other charges?
A)
B)
C)
D)
E)
a
b
c
d
e
5. An electron traveling horizontally enters a region where a uniform electric field is directed
upward. What is the direction of the force exerted on the electron once it has entered the field?
A)
B)
C)
D)
E)
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to the left
to the right
upward
downward
out of the page, toward the reader
Name ___________________________________ (print clearly on each page)
Problem #2 (30 Points)
A small spherical insulator of mass 8.00 x 10-2 kg and charge
+0.600 C is hung by a thin wire of negligible mass. A charge of
-0.900 C is held 0.150 m away from the sphere and directly to
the right of it, so the wire makes an angle q with the vertical (see
the drawing). Find (a) the angle q and (b) the tension in the wire.
It is suggested that you use symbols in your work until the end.
Suggested
variables
are
indicated
in
the
figure.
l
q1
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q2
Name ___________________________________ (print clearly on each page)
Problem #3 (30points 10 points for each part)
The drawing shows three charges, labeled q1, q2, and q3. A
Gaussian surface is drawn around q1 and q2.
(a) Which charges determine the net electric flux
leaving or entering the Gaussian surface? (Explain)
1
(b) Which charges produce the electric field at the point P? (Explain)
(c) A point charge q is located at the center of a cube of side a. How much flux leaves
the cube through one of its faces?
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Name ___________________________________ (print clearly on each page)
Problem #4 (20 points)
A small drop of water is suspended motionless in air by a uniform electric field that is directed upward
and has a magnitude of 8480 N/C. The mass of the water drop is 3.50 x 10-9 kg.
(a) Is the excess charge on the water drop positive or negative? Why? (10)
(b) How many excess electrons or protons reside on the drop? (10)
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