solmidterm2lec2

Solmidterm2lec2 - Name StudentID Section Number PhysicsifiB Spring 2008 Lecture 2 Midterm 2 Version B I Please write your name on every sheet of

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Unformatted text preview: Name: StudentID: Section Number: PhysicsifiB Spring 2008 Lecture 2 Midterm 2 Version B I Please write your name on every sheet of the exam. 4- Closed boolr, one 335 index card in your own writing is allowed. Non pro~ grammable calculators are allowed. c If a problem is ambiguous, notify the instructor. Clarifications will be written on the blackboard. Clieck the board occasionally. a Time for exam: 50 minutes c There are three questions, check that your exam has all 6 sheets. a When applicable draw diagrams and show your work. Partial credit will be given for significant progress towards the solution. Partial credit will not be given for random1 unit-less numbers left for the TA to decipher and interpret. - The permittivity ofii‘ree space is given by £0 = 8.854 X 10—]2 Cg/(N 4112). You might also find it = 1/(élrr50) --= 8.988 X 109 N - rug/C2 l'ielpful. - The problems as well as their a)—d)/e) parts are ordered in increasing difficulty. You might find it advantageous to work your way into each problem and attack the {ll—e) parts at a lai‘ier stage. Remember that partial credit will be given for the right idea or reasoning. - If you cannot figure out part or b) the result of which you need in a later part. you are provided Ean alternate value (’if you cannot figure out, assume State clearly if you decide to take the alternate value to be able to receive full credit for that later part. 0 Stop your work when the time is up - an announcement will be made. If yOu continue your work-after the announcement is made 5 points will be taken off the exam immediately. Good Luck !! Please do not write in this box [—Problem Points 1'. Problem 1: Multiple Choice 3) (lpt) Check that you have written your name, student ID number and section number on the first page of the exam. Please write your name on every sheet of the exam. b) Consider a region of uniform field as shown below Points 13, C, D, and E are all a distance d away from from point A. Between point A and which point is the largest potential difference? (a) (VB — VA) largest (VD — m largest (c) [V5 — VA) largest (d) they are all the same (e) {VC- — VA) largest c} A battery of voltage V is attached across a cylindrical wire resistor of length L and cross~sectional area A, a current I flows. If I double the area of the resistor (but attach it to the same battery), what happens to the drift velocity of electrons (vd ) in the new resistor? (a) W decreases. (T)? Jd stays the same. (e) not enough information to answer. (cl) the magnitude of ed is unchanged but the direction is reversed. (e) ed increases. M Va A V: ll 3 ,3.- < 3-— 3? cl) (ilpts) Three capacitors of the same capacitance are arranged in the following configurations, If the same voltage is applied to all of them, rank the stored charge of the configurations. %AHW iii} a m (fllQ1>Q2>Qa>Qa “3) Q3 > Q2 > Q1 i> Q4 (‘3) Q2 > Q3 = (94 > (21 (‘1) Q] = Q2 = Q3 = Q1 (‘3‘) Q2 > Q‘I > (23 > Q1 @Q2>Q3>Q:I>QI 0:.9 CF C+ 42: %c 3 CL: u ‘l O Q=CAV Somafi C e) (dpts) The following graph gives the charge density of a spherically symmetric charge distribution as the function of the radius a". P R1 R2 1' Which of the following plots best represents the electric field of the shell as a function of radius? E“) (1) Eu) (2) EU) (4] I Em (5) (a) case 5 t (b) We 4 Wis! ELK 00 c lmarwk (c) case 3 I (d) case 2 . (e case 1 — additional space for Calculation (Please clearly mark which problem you are working on) - :2 LO Problem 2: A charge Q; = +5.00 X 10"'3 C is located at $1 = 0, y: = 50.0 cm a charge Q2 : +5.00 X 10—” C is located at :52 = 0,192 = —50.0 an. Neglect any gravitatimial force in this problem. a) (Supt) Calculate the m agnitudc and direction of the force the fixed two charges excert on a test charge Q0 : —3.00 x 10—6 0 and mass mo 2 3.00 x 10—3339 which is located at ya = (J and :30 = 1' (Le. find the expression for arbitrary 3;). @1620 r41 __ A "4‘: F' ID Frat Wig H1 X Cla‘la'liom l {(0 Q0 (afl- (XZ—r qul- 2 hm; : {please tum. over) cox b) (5pt) Calculate the work required to move the test charge Q0 from infinity to yu = 0,550 = 200 cm PomiikU—Q V" Mi 6114'621 "--r c) (6pt) The test charge is released from rest at ya = 0,529 : 200 cm. Find an argument that the test charge will cross the yum-(is at y = 0. What is the velocity of the test charge when it creSses the y-axis ? iHaQ-aciT/b, Vuf y mmc_l-itu i3 Mo :‘AWL 'qu I ’1’“ 1, 9;.) m fltuflucukm 1147' @‘fimz is 22m- rtr“ Y yer:— 0 ALL ~+ AK 1' 0 Problem 3: Electrostatic cylinders A long cylindrical shell of negligible distance is a radius a" = 5.00cm away from the x—axis (see Figure (a) It carries a uniform surface charge density J = —10.0 pie/1112. The permittivity of free space is given by so = 8.854 x 10‘12 CQ/(N ‘ m2). You might also find It =1/(47r60}= 8.988 X 109 N - 1112/02 helpful. Note: You can treat the cylinder as effectively infinitely long L >> T" and L >> R. To receive full credit you have to derive the electric field using Gauss law, integration over a charge distribution or any other method you think works. Simply quoting the results is not enou h. _ ' g ' lLl—cim .— for (a) forflaj snd(c) L {please tum a ver‘) a) (tint) Find the magnitude and direction electric field due to the cylindrical shell at a radius 12}: 14 cm away from the x-axis. b) (513E) Suppose the first cylindrical shell is new surrounded by an second metal cylindrical Sllcll. The second shell is initialyl isolated and has a radius R = 8.00 cm, see Figure 4 b). Find the electric field at the radius i" = 1&1 cm. Neglect the thickness of Lhe cylinder. Explain your reasoning. “i: Sc-we M a) he £0 c) (6131;) The larger cylindrical shell is now grounded, i.e. its outer surface is connected to earth. What is the electric potential due to this setup at the radius 9" = 14 cm ? Explain your reasoning. E: O Crmti'éiA—IL 5P, (Viz/mi» by G'wmss; . Av ._= 0 0147 FM?’ Ong+SiOLIL - Sit/{Q My gm; K ...
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This note was uploaded on 10/21/2008 for the course PHYS 6B taught by Professor Wu during the Spring '08 term at UCLA.

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Solmidterm2lec2 - Name StudentID Section Number PhysicsifiB Spring 2008 Lecture 2 Midterm 2 Version B I Please write your name on every sheet of

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