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Ch17 HW4 S2010 (Homework)
Kiyaniah Tilghman
PY 208, section 003M, Spring 2010
Instructor: Keith Weninger
Current Score : 30 / 30
Due :
Monday, February 15, 2010 12:30 PM EST
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Points
1 2 3 4 5
4 7 8 10 1
Total
30/30 (100.0%)
Description
Round trip potential difference; Potential at a point; Potential difference in an insulator; Energy
density
Instructions
Reading: Sec. 17.617.9
The due date for this assignment is past.
Your work can be viewed below, but no changes can
be made.
Question: MI3 17.P.094.alt01
A highly charged piece of metal (with uniform potential throughout) tends to spark at places where
the radius of curvature is small, or at places where there are sharp points. The breakdown electric
field strength for air is about 3
10
6
V/m.
(a) It is possible to calculate the maximum possible potential (relative to infinity) in air of a
metal sphere of
10
cm radius. First, what is the maximum charge you can put on this
sphere?
3.3e6
3.33e06
C
For that amount of charge, what is the potential of the sphere relative to infinity?
2.97e5
3.00e+05
volts
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Notes
(b) Next, calculate the maximum possible potential relative to infinity in air of a metal
sphere of only
0.5
mm radius. What is the maximum charge you can put on this sphere?
8.3e11
8.33e11
C
For that amount of charge, what is the potential of the sphere relative to infinity?
1.494e3
1500
volts
These results are related to the fact that if a piece of metal has a small radius of curvature, it will
spark at relatively low potential relative to infinity.
Solution or Explanation
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