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I.
Multiple Choice: (50 pts total) Please mark the answer that is MOST correct on
this sheet and on your bubble sheet.
1) At the atomic level the electrostatic force dominates over the gravitational force by a factor of 10 39. Why does
gravitation dominate over the large scales of the universe?
a) gravitation does not fall off as quickly as the electrostatic force.
b) the electrostatic force is weak at long distances.
c) magnetic forces tend to cancel the effects of electric forces
d) moving objects tend to be unaffected by the electrostatic force
e) charges cancel creating electrically neutral bodies
2).Gauss’ law is useful for calculating electric fields that are
a) symmetric.
b) due to point charges.
c) uniform.
d) due to continuous charges
3) Find the magnitude of the force on the -10nC charge in units of 10-3N.
a) 1.27
b) 2.27
c) 3.27
d) 4.27
e) 5.27
4) An electron is found to accelerate to the right at 1.3x10 4m/s2 in a uniform electric field. What is the magnitude
and direction of the field, in units of 10-8N/C?
a) 7.4, to the left
b) 8.8, to the left
c) 7.4, to the right
d) 8.8, to the right
5) A charge q=4.42 μC rests at the center of a cube of side a=1.0 mm. Find the magnitude of the electric flux
through the cube in units of 105 Nm2/C
a) 5.0
b) 6.0
c) 7.1
d) 8.1
6) A small 2.0 g ball is suspended by a 20.0 cm string in a uniform electric field E=Ei, where E=1.0x103N/C. If the
ball is in equilibrium when the string makes an angle of 15 o with the vertical, what is the net charge on the ball in
units of 10-6C?
a) 0.7
b) 1.1
c) 4.0
d) 5.3
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7) Given an infinite line charge of λ=3.0x10-16C/m, find the magnitude of the acceleration on a proton a distance of
1.1mm from the charge in units of 105m/s2.
a) 1.7
b) 2.8
c) 3.7
d) 4.7
8) A glass rod is rubbed with silk and brought near little pieces of paper. The pieces of paper are found to be
attracted to the rod. What has been exchanged between the silk and glass rod to make this occur?
a) neutrons
b) electrons
c) protons
d) neutrinos
9) Inside of a conductor in electrostatic equilibrium the electric field is:
a) uniform
b) radial
c) divergent
d) zero
10) Given a quarter ring of charge Q=1.0μC distributed uniformly over its length and radius a=2.2mm, find the
magnitude of the electric field at the center of curvature, P, in units of 108N/C.
a) 2.5
b) 5.1
c) 10.3
d) 16.7
11) From 10), if the charge Q was instead a point charge a distance a from P, the magnitude of the point charge’s
electric field would be:
a) greater than the ring’s
b) less than the ring’s
c) equal to the ring’s
12) From 10), if we were to find a point a distance r from point P, such that r>>a, what would the electric field look
like?
a) kQ/r2
b) kQ/(r-a)2
c) zero
d) kQr/(r-a)3
13) Calculate the electric flux through the surface shown below. Give your answer in units of Nm 2/C.
a) 1.0
b) 2.0
c) 3.0
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Worked Problems: Show your work and explain your reasoning for full credit.
II.(30 pts) Point charge and charged insulating SPHERICAL shell.
A point charge Q is located at the center of an insulating shell
of inner radius a and outer radius b with a uniform charge
distribution of total charge -Q.
a) (3 pts) On the diagram at right indicate the direction of
the field lines from the inner charge Q (be sure
to label clearly).
Q
b) (3 pts) On the diagram indicate the direction of the field
lines from the outer charge distribution –Q.
c) (8 pts) Using Gauss’ law find the electric field for r<a
d) (8 pts) Find the electric field for r>b
e) (8 pts) Find the electric field for a<r<b.
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