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Unformatted text preview: one of the electric field vectors in one of the d iagram s you have created . If
a positively charged object w ere placed at the tail end of that vector, w hat w ould be
the d irection of the force on it? What if it w ere a negatively charged object? H ow
d oes the m agnitud e of the force com pare to that of the force at a d ifferent point in
space w here the electric field vector is s horter or longer? CON CLUSION
H ow d oes each of the com puter-generated d iagram s com pare w ith your correspond ing
pred ictions? What part of your pred iction, if any, d iffered from the result? Why?
Suppose you placed a positively charged point object near the d ipole at three d ifferent
locations. If the object began at rest, how w ould it m ove? What about if it started w ith
som e given initial velocity?
Overall, w as your pred iction successful? Why or w hy not? 13 ELECTRIC FIELD VECTORS – 1302Lab1Prob1 14 PROBLEM #2: ELECTRIC FIELD FROM A D IPOLE
You have a su m m er job w ith a solar pow er com pany. To m easu re the electric field s
prod uced by solar cells the com pany plans to use cond u ctive paper. They w ill arrange
the cells on the paper and m easure the field at d ifferent points on the paper . You are
assigned to test the sound ness of this process for m easuring the field s by using it to
d eterm ine the electric field created by a sim ple pattern of charged objects. You create a
tw o-d im ensional d ipole field by giving tw o parallel m etal rod s opposite charges w ith a
battery w hile their tip s are in contact w ith a sheet of cond u cting paper. You then
m easure the electric field in the paper. To see if the paper can be used to correctly m ap
an electric field you first m ake a d etailed qualitative pred iction of the electric field
prod uced by an electric d ipole at d ifferent points in space.
Instructions: Before lab, read the required reading from the textbook and the laboratory in its
entirety. In your lab notebook, respond to the warm up questions and derive a specific prediction
for the outcome of the lab. During lab, compare your warm up responses and prediction in your
group. Then, work through the exploration, measurement, analysis, and conclusion sections in
sequence, keeping a record of your findings in your lab notebook. It is often useful to use Excel to
perform data analysis, rather than doing it by hand. A t the end of lab, disseminate any electronic
copies of your results to each member of your group.
Read : Tipler & Mosca Chapter 21 sections 21-1 – 21-5. It also m ight be a good id ea to
review Chapter 1 Section 1-6 & 1-7. EQUIPMEN T
You h ave e lectrostatic paper, tw o brass r ods (to serve as
e lectrod e s), banana cables , a lligator clips, a b attery and a
w ood block to increase contact pressure betw een the
e lectro d es and the paper.
Measurem ents w ill be m ad e
u sing a Digital Multim e ter (DMM) set to read volts
connected to a p in tip probe . You w ill also have the EM
Field p rogram . A w hite sheet of paper w ith a grid sim ilar
t o the grid on the conducting paper is usef ul for record ing
t he field (do not w rite on the conductive paper). O verhead view of s etup . Read the sections Electrostatic Paper and A ccessories a nd T he Digital M ultimeter (DM M ) in
the Equipment a ppend ix.
If equipment is missing or b roken, submit a problem report by sending an email to
l email@example.com . Include the room number and brief description of the
p roblem. 15 ELECTRIC FIELD FROM A DIPOLE – 1302Lab1Prob2 WARM UP
1. D raw a picture of the d ipole, (one positive charge and one negative charge separated
by a d istance d). Label the charged point objects “+” and “-”. Clearly d efine an x-y
coord inate system .
2. C hoose an arbitrary position on the d ip ole d iagram . At this position , d raw tw o
vectors, one each to rep resent the electric field d ue each 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.) H ow should the length and d irection of
each vector d epend on the position relative to each charged object? What law
governs this? Measure the d istance from each charged object to the point w h ere you
are d raw ing the vectors to ensure the vectors have correct relative lengths.
3. D raw a d arker vector representing the TOTAL e lectric field at that point. Rem em ber,
a total, or net, electric field is constructed at a given position using the law of
superposition (vectors ad d accord ing to the tail-to-head vector sum rule).
4. Repeat this process at d ifferent, system atically chosen points (i.e., a grid ) until you
have a reasonable m ap of the electric field in the space surround ing the d ipole.
Where is the field the strongest? The w eakest? What is the d irection of the field at
d ifferent points along the d ipole’s tw o d ifferent axes of sym m etry? Sketch the
electric field as function of position along the tw o axes of sym m etry (tw o d ifferent
graphs). PRED ICTION
D eterm ine the physics task from the problem statem ent, and then in one or a few
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
- Spring '14