PHYS 211 Exam 1 with Solution, Fall 2011

PEYSICS 2U Qutu I TIME:60 minutes October 25,2011 DO NOT OPEN THIS EXAM BEFORE YOU ARE TOLD TO BEGIN NAME IDNumber Section EO L)Tio ru Useful information eo=8,85x10'12 c2lN.m2. E Check if solution is continued on the baclc Score: Part A: Multiple choice questions (18olo) t. (3o/ol Two charged particles, Q1 and Q2, re a distance r apattwith Q2 = 5Q1. Compare the forces they exert on one another when F1 is the force Q2 exerts on Q1 and F2 is the fotce Q1 exerts o^Q2. a. b. c.o e. F2 = 5F1. F2 = -5F1. F2 = F1. E2= -F1. 5F2 = F1. 2.Q%) A balloon is charged with Q and infln1s6 leading to the increase of its radius, how does the electric field inside and outside (at a distance r from the ce,nter) changes? a. lncrease and increase b. lncrease and decrease c. Decrease and decrease d. Decrease and increase @None of the above 3. (3%l A hemispherical surface ftalf of a spherical surface) of radius R is located in a uniform elecuic field of magniftrde E that is parallel to the axis of the hemisphere. What is the magnitude of the electric flux through the hemisphere surface? @ d.'E b. 41R'E/3 a c. 21R'E/3 d. ,ft'E/2 e. ,rnzn/g E Chcck if solution is continued on the baclc Scorc: A. pr/"1 A spaceship encounters a single plane of charged particles, with the ' charge per rurit area equal 6 o . The electric field a short distance abov-e tile plane has magnitude - and is directed to the plane. o a. fi'V*At"t , r o @ f 'v"w^dicular o c. i, fardtet d. g, p"tp"t dicular 6o 2o e. fr, f*utt"t 5. (3%) Equipotentials are lines along which a. the electric field is constant in magnitude and direction. b. the electric charge is constant in magnitude and direction. c. maximum work against electrical forces is required to move a charge at constant sPeed. @ a chige may be mwed at constant speed withoutwork against electrical forces. e. charges move bY themselves. 6 (g%lA series of 3 uncharged concentric shells surround a small central ct arge q. The ctrarge distriUuted on the outside of the third shell is a. -3q. b. -(tn3)q @ +q' d. +(n3)q. e. +39. El Cnect if solution is continued on the back Score: PartB- Problems (82 %) l. Q0%) A small, 2.00-9 plastic ball is suspended by a 20.O-cm-long string in a uniform electric field as shown in the Figure below. If the ball is in equilibrium when the string makes a 15.0o angfe with the verticaf what is the net dtarge on the ball? E = 1.oo x toPi N/c ----------------+ + 20.0 cm €> 1= ru tlal -€ @ ry s,Tz# - E 5.Z5xI0 E Check if solution is continued on the back. Score: &ou^'5 A"- ?ht Qu,/erA. V C Wc ,*/rr/ //, Gar*,x-^ fu, (o.s.)^f )"r/ 4 yJr*, cao'lr'2./ ^ fu, 7,r)r^ :e) =) Ar3 f ,ro z E fro 3 afrzE(,rr)| +#@ h e Vt72t4'c4 omr1,c- al /1. Q,,.r" : * a<..*/;V fr; Goro','> (.''(/ oL"e r/,cts;]*w :wa 2.Q7%) Gauss taw ,.(ll%) consider a hydrogen atom formed of one protou and one erectron assumed to :tr*'tr"und at ";n";tG;;;;" rr*, ari".ni,ilt. ,roni. nerd at a c. (to/o) What is the electric field at r>a? 4f ft )a ., Qartn's 4r*, 4/"Ua l- /-ra b.(8%) What is the total flux across a, x=aRi _ - "' r'rar nux across a cube centered at the proton and with side f"hll k act?tb ^ eoL" *rrhrU dr, te pz,h, f-, ,-t 4.s 4 z%. 4 m q";@.o)) ; o =d7 -/ El Cnect if solution is continue.d on the back 5 Score: 3.Q5%) A thin rod exrends arong the z-axis from e = -d to z = d.The rod carries a l"rl{r: charge g uniformly aiJtrituteo along its length ia *iu charge a*ritv 1,=e/2d. (a)(12%) calculate the elechic potential at a point z> d alongthe z-axis. 7 ^ g- . ttl de /r"'rt 'rn n/r"mn/ r) tut. A*f d/ *) dI " 2/O Y/=l, U = h") #, u ? (bx8%) what is the change in potential energy if an erecton moves fron z = 4d to z V (e'3l\ = 3d2 El Cnectifsolutioniscontinuedonthebaclc 6 r \ /'/+d v(2,!,4 =!,.\% lrh /a/ "d \ , ) x,1.207ft\a = lo.2 U ?- Tl. f7"rt-/,v/ uzu26/ aU- g ,_ =%)) Score: (c)Q%) If the electon started out at rest at the point z = 4d, what is its velocity at z = 3d? tx/c r'ne il" AwuWEm A *'% 4 />Ytf s- b('/ "A fnytQz onl">tff(*\ aq)e 0 f 3l_6_ = b'*. T :- )Y =A J b$ V /ou *| eL -*ot/ lrt^ 4 k^ d 6J1------1 L-- rl ' r \ r t t 2 ^ X V Eqt - % = dbt _u,))Jry H,= @1fV.) What is the electric field at aporntz > d? W. /,ohz /'# ; )/'fr;+'/ P il- ;;;:'J'- fe t/*'^rbh -, (, E^ 0Eu E Check if solution is conthued on the back' Score: