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Unformatted text preview: ector at any point near any given charge d istribution. Instructions for use of the
program are in the program .
If equipment is missing or broken, submit a problem report by sending an email to
l [email protected] . Include the room number and brief description of the
p roblem. WARM UP
1. D raw a positive point charge. Using the electric field formulation o f Coulom b’s law ,
construct the electric field vector m ap for the positive point charge. (Rem em ber that
you can und erstand the electric field by consid ering the electric force on a positive
“test charge” placed at that point.) Make sure to clearly d efine an x-y coord inate
system . As you construct your m ap, pay careful attention to how the length and
d irection of the electric field vectors vary at d ifferent points in space accord ing to
Coulom b’s law for electric field s. Sketch a graph of the electric field as a function of x
and also as a fu nction of y.
2. Repeat question 1 for a negative point charge.
3. Repeat question 1 for a d ipole charge configuration (one positive charge and one
negative charge separated by a d istance d.) Recall from the reading that m ultiple
11 ELECTRIC FIELD VECTORS – 1302Lab1Prob1
v ectors at a single point are com bined using the law of superposition (vectors ad d
accord ing to the tail-to-head vector sum rule). Accord ing to your coord inate system ,
w hich axis (x or y) is the parallel axis of sym m etry? Which is the perpend icular? PRED ICTION
D eterm ine the physics task from the problem statem ent, and then in one or a few
sentences, equations, d raw ings, and or graphs, m ake a clear and concise pred iction that
solves the task. EXPLORATION AN D M EASUREMEN T
In the fold er P hysLab o n the d esktop, open
EM Field a nd click anyw here in the w ind ow
for the instructions. From the S ources p ulld ow n m enu, select 3D point charges. Drag any
p ositive charge to the center of the w ind ow of
EM Field . From the Field and Potential p ulld ow n m enu (show n to the right), select Field
M ove the cursor w here you w ould like to place a field vector and click the m ouse
button. An electric field vector should appear w ith d irection given by the arrow head
and the relative m agnitud e given by the length . Repeat this proced ure over consistent
intervals (i.e. a grid ) in the horizontal and vertical d irections until you have created a
reasonable m ap of the electric field . Using the S how grid a nd Constrain to grid features in
the D isplay m enu w ill m ake this process easier. Sw itch to another kind visual
representation of the electric field by clicking Field and Potential: D irectional arrows from
the m enu. In this representation, the relative m agn itud e is given by the color. To start
over, click D isplay: Clean up screen . When you are finished , save your result by printing
to pd f.
N ow , sw itch to field lin es representation of the electric field by clicking Field and
Potential: Field Lines. Save this result to pd f. Discu ss in your group and note in your
notebook: W hat are the d ifferences and sim ilarities betw een the "field lines" and "field
vectors" representations of the electric field . A re they equally usefu l? Why or w hy not?
Se lect your favorite electric field vector representation (either length or color
m agnitud e, n ot field lines) and repeat the above exercise for the electric field of a
negatively charged point object. Save your result to pd f. Sw itch to the field lines
r epresentation and save the result to pdf. Then, sw itch back to the vector field
representation. Discu ss in your group and note in your notebook: H ow d oes the vector field com pare to that for the positive point charge?
12 ELECTRIC FIELD VECTORS – 1302Lab1Prob1 W hat effect d oes increasing the change value have on the vector field m ap? Finally, create a d ipole by d ragging tw o equal but opposite point charges into the
w ind ow . Using your favorite electric field vector representation, m ake a m ap of the
electric field caused by a d ipole. It is especially important that you make your map by
placing vectors on equal increments in the horizontal and vertical directions. Save your result
to pd f. Sw itch to the field lines r epresentation and save the result to pd f. Then, sw itch
back to the vector field representation.
IMPORTAN T: Dissem inate electronic copies of your results to each m em ber of your
group. A N ALYSIS
C onsid er your d ipole electric vector m ap. Sketch the electric field as a fu n ction position along the parallel axis of sym m etry.
Repeat for the perpend icular axis. H ow d o these graphs com pare w ith your
pr ed iction? If you are very far away from the d ipole, how d oes the field com pare to that of a
single point charge? H ow d oes it com pare if you are very close to one of the point
charges? In general, w here are the m axim a and m inim a of the electric field ? Does your
answ er d epend on w hether you are consid ering one or the other axes of sym m etry?
Why or w hy not? C onsid er...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
- Spring '14