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General Physics – PH 203
Midterm I (Ch 25 - 28)
October 21, 2004
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Name:____________
Exam is closed book, closed notes. Use only your note card.
Write all work and answers in the papers provided.
Show all your work and explain your reasoning (except for true/false or multiple choices
ones)
Partial credit will be given. No credit will be given if no work is shown (except for
true/false or multiple choices ones)
Part I – True or False: For questions 1 – 5, state whether each statement is true or false.
1. The electric field lines never diverge from a point in space.
2. Any charge q can be expressed as q   ne where n is an integer and e is the charge of an
electron.
3. The result that E = 0 inside a conductor can be derived from Gauss's Law.
4. Electric field inside a conductor is zero only if the conductor is in electrostatic
equilibrium.
5. If the net charge on a conductor is zero, its surface charge density must be uniform.
Part II – Multiple choice questions: For questions 6 – 15 select the only one choice that best
answers or completes each statement.
6. How far June must travel to get away from the earth’s gravitational field?
A) To a region above the earth atmosphere.
B) To a region well beyond the moon.
C) To a region beyond the solar system.
D) To a region beyond Milky Way (about 80,000 light years away).
E) …forget it body, you can’t travel far enough.
7. Two charges Q1 and Q2 are a distance r apart. If all quantities are doubled, the force of
charge Q1 on Q2 would
A) not change.
B) halve
C) double.
D) quadruple.
8. A charged insulator and uncharged metal
A) always repel each other electrostatically.
B) exerts no electrostatic force on each other.
C) always attract each other electrostatically.
D) may attract or repel depending on the sign of the charge on the insulator.
9. Which of the following statements is true for metallic conductor?
A) It cannot carry a net charge.
B) If it carries a net charge, that charge must be distributed over its volume.
C) If it carries a net charge, that charge must be distributed over its surface.
D) It must be at zero absolute potential.
E) The electric field inside the conductor must be constant.
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10. If the mass of a planet is doubled with no increase in its radius, the escape speed for this
planet will be
A) reduced by a factor 1.4.
D) increased by a factor of 2.0.
B) reduced by a factor 2.0.
E) unchaned.
C) increased by a factor 1.4.
11. An uncharged metallic shell is placed near a small negative charge -q as shown, but the
charge and the shell are not in contact. Which of the following statements is correct?
A) A net positive charge is induced on the outside
-q
and a smaller negative charge appears on the
inside surface of the shell.
B) A net positive charge is induced on the outside
and a larger negative charge appears on the
inside surface of the shell.
C) A net negative charge is induced on the inside
and a positive charge of equal value appears
on the outside surface of the shell.
D) None of the above.
12. A conducting rectangular plate is connected to ground through a switch. The switch is
initially closed. A positive charge q is brought near the plate as shown, but the charge is
not brought in contact with the plate. While the charge is near the plate, the switch is
opened and then the charge is removed. What is now the charge state of the plate?
A) It is negatively charged
B) It is positively charged.
C) It is uncharged.
D) It can be any of the above depending
+q
on the initial charge on the plate before
the charge +q was brought nearby.
13. At a particular region of space, a charge q experiences no net force. We can conclude that
A) There must be no charges present nearby.
B) If there are any charges nearby, then they must have the same sign of q.
C) If there are any charges nearby, then they must have the opposite sign of q.
D) If there are any charges nearby, the net positive charge must equal the net negative
charge.
E) None of the above.
14. In a charge-free region of space, a closed rectangular box is placed in an electric field.
The total electric flux through the surfaces of the box is zero. For this to happen
A) the field must be uniform.
B) the box must be oriented in a certain way.
C) the box must have cubical symmetry.
D) the electric field lines must leave through all surfaces.
E) this will happen anyway - total flux is zero no matter what.
Physics 203 –Midterm Exam I October 20, 2005
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Part III – Questions and Problems
Please explain or show your work clearly for each of the following questions or problem.
1. The figure shows the electric field lines for two point charges separated by a small
distance. How are q1 and q2 related? Explain.
q2
q1
2. A 10 nC point charge is inside a hole in a
conductor. The conductor has a net charge of
+10 nC.
(a) What is the total charge on the inside
surface of the conductor? Explain.
(b) What is the total charge on the outside
surface of the conductor? Explain.
15. Four charges, each +q, are placed on the corners of a square with side of length a. The
square is in the yz-plain with its center at the origin. Point P is on the x-axis, a distance x
away from the center of the square.
a) Calculate the electric potential at point P as a function of x. (Assume electric potential
to be zero at infinity).
b) Calculate the electric field at point P (magnitude and direction).
17.
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An electric field E  (50000 N / C )iˆ causes the 5.0 g
the figure to hang at a 20  angle. What is the charge on
ball?
Physics 203 –Midterm Exam I October 20, 2005
ball in
the
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Physics 203 –Midterm Exam I October 20, 2005
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