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Lab 03 S10 EField of Continuous Object  VPython (Lab)
Kiyaniah Tilghman
PY 208, section 210, Spring 2010
Instructor: Kelly Patton TA
Current Score : 50 / 50
Due : Wednesday, February 10, 2010 04:50 PM EST
About this Assignment
Question
Points
12 3 4 5 6
2 6 10 12 10 10
Total
50/50 (100.0%)
Description
Electric field of a continuous object  Vpython and Whiteboard
Instructions
Part 1: VPython  Efield of a Rod Instructions
Part 2: Whiteboard problem(s)
Group Members (Group 6) Tilghman, Kiyaniah Vargo, Andrew Crawford, David
The due date for this assignment is past. Your work can be viewed below, but no changes can
be made.
1. 2/2 points All Submissions Notes Only the Recorder for your group should submit this assignment.
Who was the Manager of your group for this lab session? (Enter first and last name; for example:
Kim Jones.
Kiyaniah Tilghman
Key: Name Who was the Recorder?
Andrew Vargo
Key: Name
Who was the Skeptic?
David Crawford
Key: Name
Who was the Summarizer? (If none, type "none".)
none
Key: Name 2. 6/6 points All Submissions Notes In lab you wrote a VPython program to calculate the electric field of a uniformly charged rod at a
single observation location, by approximating the rod as a row of point charges. These questions
apply to that program.
Make the following changes to your program:
Total charge on rod: 2e08 C
Observation location: < 0.75, 0.8, 0> m
Number of point charges: 25
Adjust the scale factor as necessary.
All the spheres, and the orange arrow representing the electric field, should be clearly
visible.
The following question checks whether your program is correctly calculating and displaying the
electric field at the observation location. To answer them you will need to look at the value of Enet
printed after the loop has completed (at the end of the program).
What is the value of the electric field vector at the observation location, as calculated
by your program?
= <  77.1093
 77.1 , 5.15432
5.15 , 0
0 > N/C 3. 10/10 points All Submissions Notes Turn in your VPython Electric field of a Rod program here.
Before turning in your program, compare your running program to that of another group, and then show your running program to your TA.
Make sure you turn in a working version of your program, since you will not receive credit if the
program doesn't run. It's a good idea to run your program one last time just before turning it in.
Sometimes students accidentally turn in the wrong file, or an empty file. To prevent this, after
turning in the file click on its name and make sure the file looks right.You must include the
standard ".py" extension on the file name. For example, your file name could be "physics.py".
physicslab3.py 4. 12/12 points All Submissions Notes Save a copy of your program and rename the file. This way you won't lose the version that you
have submitted and you can make the changes below without worry.
Make the following changes to your program:
Total charge on rod: 5e08 C
Observation location: < 0.5,  1.2, 0> m
Number of point charges: see questions below
Adjust the scale factor as necessary.
One way to decide if your calculation is "good enough" is to observe how much the result
changes when you use more pieces in your model of the rod. The following questions
focus on how the accuracy of your calculation depends on the number of point charges
used to approximate the rod.
When you approximate the rod by 5 pieces, what is the calculated magnitude of E,
rounded to the nearest integer?
= 405.5219
406 N/C for 5 pieces.
When you approximate the rod by 10 pieces, what is the calculated magnitude of E,
rounded to the nearest integer?
= 284.7624
285 N/C for 10 pieces.
When you approximate the rod by 25 pieces, what is the calculated magnitude of E,
rounded to the nearest integer?
= 294.3549
294 N/C for 25 pieces.
When you approximate the rod by 50 pieces, what is the calculated magnitude of E,
rounded to the nearest integer?
= 294.3353
294 N/C for 50 pieces.
When you approximate the rod by 75 pieces, what is the calculated magnitude of E,
rounded to the nearest integer?
= 294.3327
294 N/C for 75 pieces.
Look at the results you have tabulated above. If you are interested in an answer that is
accurate to 3 significant figures, you would need to use 25
25 pieces in your
model. 5. 10/10 points All Submissions Notes Do this problem on a whiteboard.
Consider a thin glass rod of length L= 3 m lying along the x axis, as shown in the diagram. The rod
carries a uniformly distributed positive charge Q = 75 nC (nanocoulombs). At a location a > L, on the x axis 0.46 m to the right of the right end of the rod, what is the electric
field due to the rod?
Follow the standard four steps.
(a) On a whiteboard draw a diagram to explain how you will cut up the charged rod, and
draw the ! contributed by a representative piece.
(b) Express algebraically the contribution each piece makes to the electric field. Be sure
to show your integration variable and its origin on your drawing.
(c) Write the summation as an integral, and simplify the integral as much as possible.
State explicitly the range of your integration variable.
What is the electric field at location a?
= < 424.1
424 , 0
0 ,0
0 > N/C
N/C
(d) Do at least two checks to test whether your result is reasonable.
Explain how you solved this problem, including your choice of origin, integration variable,
integrand, integration limits, and the checks you performed. Your whiteboard work may
count as an adequate explanation: check with your instructor.
whiteboard!
Key: Whiteboard work.
6. 10/10 points All Submissions Notes Do this problem on a whiteboard
A large, thin plastic disk with radius R = 1.9 meter carries a uniformly distributed charge of Q =  2
10–5 C (Figure 15.58). A circular piece of aluminum foil is placed d = 3 mm from the disk,
parallel to the disk. The foil has a radius of r = 3 cm and a thickness t = 1 millimeter. Figure 15.58
(a) On a whiteboard, draw a diagram showing the charge distribution on the closeup of
the foil.
(b) Find the net electric field at the center of the foil.
<0
0 ,0
0 ,0
0 > N/C
(c) Calculate the magnitude q of the charge on the left circular face of the foil. You may
need to make simplifying assumptions or approximations. Hint: look at your diagram of
the foil disk, when considering how to model the charge on the foil.
2.493e9
2.49e09 C
(d) Explain in detail how you solved this problem, including all assumptions and
approximations you made. Your whiteboard work may count as an explanation  check
with your instructor.
whiteboard!
Key: We assume that the positive charge is spread out uniformly on the left side of
the foil, and the negative charge is spread out uniformly on the right side, so we can
model these two sheets of charge as a capacitor. We use the fact that the net electric
field at a location inside a conductor at equilibrium is zero. ...
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 Spring '10
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