08C 2220 Exam 2a Key

08C 2220 Exam 2a Key - Physics 2220 Spring 2008 r...

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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, multi-branch 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 current-carrying 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~"'c-5uo“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 “e-t/Ré) =3> gig“ => 1&7“: => w 3 L L i:JDOSi-2Kw*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 (EV-6V) _ 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 [Tr-F 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: : -5A-F[[0.3m)L-[0JW’:] a. g 0.795 A-mzamw 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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08C 2220 Exam 2a Key - Physics 2220 Spring 2008 r...

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