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Unformatted text preview: Physics 2220
Spring 2008 r
Examination 2 Name: e '_ W5} 1
Student ID: ‘ p , ‘ , Instructor (circle one): _ Matteson Littler _ Weathers This test consists of 7 multiple—choice"queStions and 7 freeéresporlse problems, for a total of 110
points (so that 10 points of extra credit are possible). To receive credit for the yfree~response
problems, you must .showvall’éof your work on the pages provided. ﬁDon’t hand in any eXtra sheets
or other paper. You may also earn partial credit for the some of the multiple choiCe problems if
you Show your work. 1. 99'???" Suggested procedure for solving the problems: Read each problem carefully and make sure you know what is being asked before
starting the problem. Draw a ﬁgure for the problem. List the parameters given. ‘ ” Write doWn the equations to be used. Solve for the answer symbolically. Substitute numbers into you ﬁnal equation and circle your answer. WORK THE EASY PROBLEMS FIRST” 1. (5 points) A potential difference A Vis applied across an air—ﬁlled capacitor with parallel
plates of areaA separated by a distance d. Which of the following changes will produce the
largest change in the energy stored in the capacitor? a. A is doubled. b. dis halved. I , > .. , ,; c. The volume between the plates is ﬁlled with a dielectric: material of constant K = 2.
@ A Vis doubled. 6. None of the above —— they all produce the same change in stored energy. a 4/1 $> Ca: w—‘ZGL; Cb: é2"§“=.ZC,,; Cc= KCo‘ZCo
U= $6.sz e 3049vath u ; doubt, Av 1W1“ u 2. (5 points) A potential difference A Vis applied between the ends of a wire of circular cross
section. As a result, a uniformly distributed current I ﬂews alOng the length of the wire. The
same potential difference is then applied between the ends of a Second wire of the same
material, but only half the length and half the radius of the ﬁrst Wire. Compared to the ﬁrst
wire, in the second wire the * a. current density and resistance are half as large, but the current is the same. '
b. current density is twice as large, the resistance is half as large, and the current is the
same. \ © current density and resistance are twice as large, and the current is half as large.
d. current density and resistance are half as large, and the current is twice as large.
e. current density and current are twice as large, but the resistance is the same. 3. (5 points) In a closed, multibranch circuit, the sum of the voltage differences around any
closed loop adds to zero because the potential of the nearest battery is the potential supplied to the loop.
charge is neither created nor destroyed at a junction.
capacitors tend to maintain voltage at a constant value. a.
b.
0.
@ energy is conserved in a closed loop of a circuit.
' ' ' e." energy isnot tranSfcrrned from'one type to anotherinwaicircﬁit. Kin/Murat; loop win. 4. (5 points) When a capacitor, battery, and resistor are conneCted in series, the maximum
charge stored on the capacitor a. is greater for greater resistance.
b. is less for greater resistance.
@ is independent of the resistance.
d. depends on the product of the resistance and; capacitance. R mm. m: away as? .1. I'lmwyé’fgmuottm 5. (5 points)'M_agnetic ﬁelds differ from eleCtric ﬁelds in that the force exertedon a charge q a. is in opposite directions in electric and magnetic ﬁelds. ® is parallel to an electric ﬁeld and perpendicular to a magnetic field.
0. is parallel to a magnetic ﬁeld and perpendicular to an electric ﬁeld.
d. is inythe samewdi‘rection in‘y'electric and:‘mag13etic, ﬁelds. 6. ‘is zerofor both‘if thea'charg‘ezisnot moving] ’ “W ‘5 d v.5 Fa: q’E Fm; @343 6. (5 points) A long, straight wire is oriented along an east—west line. If free electrons in the
wire ﬂow due east, the resulting magnetic ﬁeld south of the wire and in the same horizontal
plane as the wire points in which direction? (Neglect Earth’s magnetic ﬁeld.) a. east . b. west N
c. north r Tin/(1.
d. south " r _{ i
e. straight down , 13 G) straight up w ‘ I 4... E 51> $ 4" @ 7. (5 points) When an electrical appliance is turned on, the two parallel currentcarrying wires
in its power cord exert on each other I  > * a. an attractive magnetic force.
(1;) a repulsive magnetic force.
0. no magnetic force.
d. a magnetic force that acts at right angles to the plane of the Wires. 8. (9 points) A proton of mass m = 1.67 ><y10‘27 kg and charge +e moves at right angles to Earth’s
magnetic ﬁeld (B = 5.0><10‘5 T) with a speed v = 4.O><'106 m/s. Find the radius of curvature of
its orbit. « ' ww’ Lawtofkr‘lx‘ow : 834M .2.” )_ 212.. I: ’— :
ZF'W $’ “WE V“? =’\’ V“ 43 u.wo~"'c5uo“T 9. (10 pcints) A series RC circtlit is made up of a 100 Q. resistor and a 2.0 [1F (uncharged)
capacitor. At t = 0 see, a switch is closed and the capacitor is charged by a 12 V battery.
I Determine the time required for the charge to rise to 1/3 of its ﬁnal value. I ' ;.,.—t _'
Ire Q: anux “et/Ré) =3> gig“ => 1&7“: => w
3 L L i:JDOSi2Kw*6F.L(l—'g)w L” 5 8' 145 10. (10 points) Determine the equivalent ' z 3 Sui: v , 8uF
capacitance of the series/parallel :  3m}: 2111‘: ' ,
combination shown. ' 11. (10 points) Find the equivalent resistance of the circuit shown below.  12. (12 points) In the circuit shown, V1 = 12.0 V,
V2 = 6.0 V, and R = 4.0 9. Find the power
dissipated in the middle resistor. Li R  it B i/IS R1, 12 Node rule: 1.42413 .
Looprule (\e’ﬂ 100?): V.‘I.R'I3R:O Vi Vi
“ ‘j QidxM" )3 VZ+I3R‘I1R:O ‘ I i I Solue‘cw Is: I! T L ‘ 13—40
01. «I: t » , R o M“ J a. ,. ‘ I
; R g ,, ¥ I
0. R :R _ ' v c 1 s 7 ' z .::'v.v 2 * ‘ vrvf (EV6V) _
wa ohssifaie‘eiiivf Maddie (P: I3 R s =   13. a. (7 points) Find the magnetic ﬁeld at point P if
a =.15.0 cm, I) = 30.0 cm, and I= 5.0 A. Format/rt 0i Maﬁl’bﬁdolafftﬂgmy '
‘IS?IV69J4V&, @ v ‘ .r y gag? =ﬂ°1 Mahmule rm y' L ' Iran: I [TrF b‘injm’haﬂzmbaj WWW HE J P. .~> ' > Ba MW + M I.,";_3‘IT‘ .‘ — .L‘ ’ ' 415M 43%» 5 95/“. cu!" b. ( 5 points)Find the magnetic dipole moment associated with this current loop. ‘ “121w I} git/m ml; 5d”, m M“ ca“) .. , ,Wbidu rm WWW] . = ~ 1: ,A: : 5AF[[0.3m)L[0JW’:] a. g 0.795 Amzamw 14. (12 points) A long, straight, cylindrical wire of a
radius 1) = 3.00 cm has a cylindrical hollow of radius a = 1.00 cm offset from its center by a. A
current of uniform density J = 400 A/m2 k ﬂows
through the wire parallel to its axis. (The current
ﬂows out of the page in the ﬁgure, and ﬁlls the; shaded region.) Find the magnetic ﬁeld B at point P '
as shown, where P is located a distance r = 4.00 cm I
from the wire’s axis, along a radius passing through i the center of the hollow. [Hint _ In the hollow; 3, ; region, the current density giszvero, which may be{ ~
regarded as the superposition of J — J r L '0 Thiﬁle'OkS likciQSu/(Wg' pvt/{tie lo, Rig (2 MW 1 p27 ram.
Py Ctr/5‘01“; ' ‘_ Mrde
M» MWW . ...
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 Spring '00
 Littler
 Magnetism

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