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Unformatted text preview: OLD DOMINION UNIVERSITY PHYSICS 227N/232N, University Physics
Spring 2013 First Examination 8:30 am  10:20 am Tuesday 05 February, 2013
Room 142, OCNPS PROFESSOR: Dr. D. C. Cook
Answer all questions: All questions should be answered on the examination paper.
If more space is required, attach sheets to paper. Text book may not be used. Candidate's .3‘ .11. ' mug N
CONSTANTS AND EQUATIONS
80:8.8510'12(:2N_1m'2 1nC=10'9C 1pc=10‘6(:
k = 47:80 = 9.00 109 N m2 (3'2 Electron charge 6 = 1.60 x 10'19 C
k
Fe = quzqz 1‘ Electron mass rne = 9.11 x 10'31 kg
k
E = ﬁ 1‘ Proton mass m = 1.67 x 10'27 kg
r2 p
k k
U = (’11le V = % F = Eq 1. ELECTROSTATICS I (Total 25 Marks)
A charge of q1 = 30.00 uC is place at the origin 0 (position (0, 0)) as shown in
Figure 1. A second charge of q2 = 50.00 uC is brought in from inﬁnity and placed
at the position P (2.00m, 0) along the x—axis. A point R is located at (0.50m, 0) along the x—axis. Figure 1. (i) Calculate the electric force on q; qum ; .. = 3.3%‘M 1' r (2.00m? w _ n.
"a . __. ‘f‘f’ \/
A “ 7*
M”; m... ‘ ANSWERé. aaSN 4
(ii) Mum pomi‘gy‘ﬁmspair of charges.
Urlﬁj: =L(gO§’lDC 3 (—eroc— lac.)
Y C 00m} M ANSWER ' (ofK 3'
(iii) Calculate the electric ﬁeld at the point R. E' 5:; C
Y2
‘V 30240C. + (‘Sogﬂ'bc‘km ,
"10.7757 LWM‘ Ll. l“' ANSWERi selmg‘ N/c, Continued on Page 3 (iv) Calculate the potential at the point R. \j: fl = k<30l§40€ _ {DEMR A third charge of q3 = 15.00 uC is now brought from inﬁnity and placed at
position R. (v) Calculate the electric force on q3 Emmi ,» = L (geeagora'EMT + (gee—obtﬁe—‘oo E»
V‘ (o.§m)7 (l5N‘W /3 p ANSWER lcl .Z N 3‘
(vi) How much work was done to move q; to R? wr‘ﬂ o5 = — ms: / v19? (WWW? t V—Gtﬂs 3r \4°\3¢(L ' _ ..  \LseM'X =\L w +G°Ezgéﬂc ANSWER — 3923) j
._ 7.0”; + ((—soewcwse— be) :0 If}
bu : ~JI‘r (re7;):3r Jar End of Problem 1 2. COULOMB’S LAW (Total 25 Marks) Two small spheres each of mass m = 15.0 grams are hung by silk threads of
length L = 1.20 m from a common point as shown in Figure 2. When the
spheres are both given the same negative charge of q1 = q; = 2.80 uC each thread hangs at the angle of 6 to the vertical and the two spheres hang in static
. . . /_ t , ,2
equlllbrlum. 7’ P _’ O (a) On Figure 2 draw all the forces acting on each sphere. . Cc
Flgure 2. l (b) Calculate the angle 6. ._ , ,
m I»  S N Z /
aﬂovsvcgm an Is ~ LH‘H / L \ ' Q,
Q 9n. / :g‘SmB
Y7.
1 . Ce “7’ e R
*ame :' Ol1t7>§qu (him) S\ne iﬂcvﬁz 4
(ages (zﬁe'bbl ‘
\ 2: “I 
S\ne C036 00"
ANSWER
End of Problem 2. 3. ELECTROSTATICS II (Total 30 Mar s Three charged particles, q1 = 4.0 uC, q; t 4.0 uC and q3 = +4.0 uC are located at
the corners of a rightangled isosceles triangle whose two equal sides are length a 2 0.10m, as shown in Figure 3. The point P is located at the position of charge ql at
the bottom right corner of the triangle. ' C12 ,\
“o . ~
/ ' L/\
M5“ x
I \
\
\
\
\
\
\
\
\\\ D¢m
a F \ .
>0 ‘~
0 \ xV‘DY Figure 3. P ’ “\‘D V Calculate the answers to the following 3 guestions. (i) Calculate the Electric ﬁeld (magnitude and direction) at the point P in Fi ure 3. r~
g + C. qubC g\‘(\"\§vi\fl 5 Y. " “' \1— W4?“ ' t Y O‘D’Lm 0,01. '\ bf
’26?) D \ 263 = L (Ac—cc. musﬁ .. ’ 1
_ 1' k
' b 007. E ‘ ‘ vs a.
+on\ M735 H:
5.3.5.; r '732”*\0k\1 \ E sum A0“ = gov: ANSWER ’2. (95' c to N/C. Direction a 3 ° (12 Marks) [Continued on Page 6 (ii) Calculate the Electric Potential Energy of this system of 3 charges. 0’ \¢°\\°\' L) =lc («145 (oQC’LlE'bq »
{Kim Y' ANSWER — \ﬁsto J. Marks) (iii) What is the electric potential at the point P? w M. \l¢ ‘t 35:23. + 14.5%)
7 _ \llozm °'\“" 6 ANSWER warms” M . ‘5 Marks) (iv) What is the electric force (magnitude and direction) on the charge q1? r. k.7_ ” Z '.
[xx E Di”! r “r p: 6: @(HC (or) A' n) /]
' \1 _ E— ” \ _,  ,
'r I“ , \L U V. [V ANSWER \H. N. Direction Q’ (+1) }5 Marks) End of Prob 3 4. CHARGE IN AN ELECTRIC FIELD. (Total 20 Marks) An electron is projected along the xaxis with an initial speed of v0 = 1.60 x 106
m/s into an electric ﬁeld between two parallel plates as shown in Figure 4. The
electric ﬁeld is uniform in the vertically downward direction, and has a magnitude
of E = 300.00 N/C. The electric ﬁeld outside the plates is zero. The plates are
separated by a distance D = 1.00 cm and the plates are of length L = 2.00 cm. The
electron enters the ﬁeld midway between the plates at x = 0 and y = 0, i.e. position (0, 0). The electron hits somewhere on the ﬂuorescent screen located at the right
end of the plates. Wew‘ﬂu'ﬂwmhhm I: ravenq umWam
Figure 4. (i) On Figure 4 label the positively and negatively charged plates. (ii)What do you know about the magnitude of the charge n each plate? L
1+: Qmml H‘s (gawk? W €\~(o0x\o"°‘cv 4 (iii) Calculate the position on the screen (along the y axis) that the electron hits the green. Also mark the location on Figure 4 and label it “e”. h f/
m L.
" <>< _ E W) 6L
\0 ’ F ./ 61/? 7 ‘ C6 (V f‘ \1 a \3 300“\Q ’ x»\' [q“vJO—‘MU q QA “Vs2B = gﬁ'S—ilvlb’w
44 _ A y _ OLQL/ Continued working on Page 8 V ' R— M.— U Fame“? (iv) If instead the projected particle was a proton, mark the approximate
location “p” on Figure 4 where you expect it to hit the screen. End of Examination ...
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 Spring '14
 ALEXANDERL.GODUNOV
 Physics

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