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Physys 202 Fall08
HW2
Due at 11:00pm on Wednesday, September 24, 2008
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Charge Distribution on a Conductor with a Cavity
Description:
Conceptual problem. Positive charge sits outside a conducting shell. What is the resulting charge distribution on
the inside and outside of the shell.
A positive charge is brought close to a fixed neutral conductor that has a cavity. The cavity is neutral; that is, there is no
net
charge inside the cavity.
Part A
Which of the figures best represents the charge distribution on the inner and outer walls of the conductor?
Hint A.1
Conductors have no internal field
At steady state, conductors have no internal electric field (otherwise, charge would flow). Therefore, the arrangement of
charges on the surfaces of the conductor must exactly cancel out any external electric field to ensure that the internal field is
zero.
Hint A.2
Charges on the cavity walls
Think about what the answer would be for a conductor without a cavity. Would there be net charges on the surface of some
imaginary sphere drawn inside of the conductor? Would this change if you removed all of the material inside of that sphere?
ANSWER:
1
2
3
Problem 22.48
Description:
An extremely long, solid nonconducting cylinder has a radius R_0. The charge density within the cylinder is a
function of the distance R from the axis, given by rho_E ( R ) = rho_0 ( (R/R_0 ) )^2, rho_0>0. (a) What is the magnitude of
the electric.
..
An extremely long, solid nonconducting cylinder has a radius
. The charge density within the cylinder is a function of the
distance
from the axis, given by
,
.
Part A
What is the magnitude of the electric field everywhere inside the cylinder (far away from the ends) in terms of
and
?
Express your answer in terms of the variables
,
,
, and appropriate constants.
ANSWER:
=
Part B
[
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MasteringPhysics
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What is the direction of the electric field everywhere inside the cylinder (far away from the ends) in terms of
and
?
ANSWER:
radially inward
radially outward
Part C
What is the magnitude of the electric field everywhere outside the cylinder (far away from the ends) in terms of
and
?
Express your answer in terms of the variables
,
,
, and appropriate constants.
ANSWER:
=
Part D
What is the direction of the electric field everywhere outside the cylinder (far away from the ends) in terms of
and
?
ANSWER:
radially inward
radially outward
Electric Force and Potential: Spherical Symmetry
Description:
Reviews the electric field and potential for a point charge in three dimenions. First asks the student for a formula,
then to choose the correct curves from a plot.
Learning Goal:
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 Spring '08
 Akgun
 Physics, Charge, Potential Energy, Electric charge, uniform electric field

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