Unformatted text preview: ure the length of the electric field vector at all points on the screen?
Where is a good place to put the configuration in ord er to get a larger num ber of
m easurem ents?
To check w hether or not you get the correct behavior of the electric field from a point
charge d o the follow ing: 38 THE ELECTRIC FIELD FROM MULTIPLE POINT CHARGES – 1302Lab2Prob1
1. Pick a useful charge value and d eterm ine several locations at d ifferent d istances r
from the center of the single point charge. (H int: Choose your locations at regular
intervals.) At each location , m easure r a nd the length of the electric field vector. In
your notebook, record the d ata and sketch a plot of the vector length as a function of r.
2. N ow , calculate w hat Coulom b’s law pred icts and sketch the values for the field
strength vs. d istance (r) on the same graph.
3. Com pare the shape of the graph to that based on the Coulom bs’ law and record your
You have to calibrate t he com puter sim ulation program in ord er to translate vector
lengths on the screen to vector m agnitud es that you calculate using your pred iction
equation, w hich are in SI units (assum e Q = 1C). You can use the d ata that you just
collected to d o this. On the com puter, plot the electric field strength in SI units vs. the
electric field in length units that you m easured w ith the ruler. Fit a line to the d ata. If
the fit is good , then you can use the fit equation to convert from electric field lengths on
the screen to electric field m agnitud es in SI units. If it is not good , then you need to go
back and repeat steps 1-3 above.
N ow , explore the d istribution of three charges. Drag tw o equal negative charges and
one positive charge of 1/ 3 the value of one negative charge onto the screen in the
configuration specified in the problem statem ent above. H int: m ake sure the charges
are accurately placed using the ‘constrain to grid’ feature. N ote the length of the electric
field vector in the fourth corner of the square. What param eter can you easily vary to
change the length of the electric field vector in that corner w hile preserving the other
cond itions of the problem ? In your notebook, note w hether or not su ch m anipulations
change the d irection of the electric field at that corner, and record the d irection. H int:
you may need to change the box size or charge magnitudes to get vectors that are large enough to
measure accurately but not so large that they go off the screen. D eterm ine a m easurem ent
p lan. M EASUREMEN T
M easure the length and record the d irection of the electric field vector at the point of
interest for several d ifferent values of the varying param eter , accord ing to your
m e asurem ent plan. Record the d ata in your notebook. A N ALYSIS
U se the d ata for the follow ing analysis (perform on Excel):
1. Using your calibration equation, convert the lengths of the m easured electric field
vectors prod uced by the com puter sim ulation into electric field strength s in SI units. 39 THE ELECTRIC FIELD FROM MULTIPLE POINT CHARGES – 1302Lab2Prob1
2. Using your pred iction equation , w hich is based on Coulom b’s law , calculate the
expected electric field m agnitud es in SI units at the point of interest for your chosen
values of the variable param eter.
3. Com pare your calcu lated electric field strength to that from the com puter sim ulation
on a plot. Also, com p are your pred iction to t he d irection of the field to that from the
com puter sim ulation. CON CLUSION
H ow d id your expected result com pare to your m easured result? Explain any
d ifferences. From your results, w hich general properties of the electric field d oes the
sim ulation faithfully reprod uce? What is the specific evid ence? 40 PROBLEM #2: THE ELECTRIC FIELD
FROM A LIN E OF CHARGE
You are a m em ber of a team d esigning an electrostatic air cleaner for the use of people
suffering from allergies. The air passage through the d evice w ill contain m any
com plicated charged electrod es. You m ust d eterm ine the effect of these electrod es on
p lant spores that cau se allergic reactions. The first step is to calculate the electric field at
every point in the air passage. Because the electrod e configuration is com plicated , your
team has d ecid ed to use a com puter sim ulation to m od el the resulting electric field .
Your task is to d eterm ine if the sim ulation results agree w ith the p hysics you know for
non-point-like charged objects. You d ecid e to test the sim ulation for the case of a
uniform ly charged rod , since this situation is sim ple enough for y ou to calculate. For
com parison w ith the sim ulation results, you d ecid e to calculate the electric field at
arbitrary points from the m id d le of the rod along its perpend icular axis and also at
arbitrary points from the end of the rod along its parallel axis.
Instructions: Before lab, read the required reading from the textbook and the laboratory in its
entirety. In y...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
- Spring '14