Physics 121 Sample Common Exam 2 Rev2 NOTE: ANSWERS ARE ON PAGE 7. Instructions:

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1 Physcs 121 Smple Common Exm 2 Rev2 NOTE: ANSWERS ARE ON PAGE 7 Nme (Prnt): 4 Dgt ID: Secton: Instructons: Answer ll 27 multple choce questons. You my need to do some clculton. Answer ech queston on the Scntron sheet usng #2 pencl. You my use bcks of the queston ppers for extr spce. There re more problems n ths sm[ple test thn you would fnd on rel exm 1. A chrge s plced on n solted, hollow metl rectngulr sold wth closed ends s shown. How wll ths chrge be dstrbuted fter whle? A) The chrge wll be dstrbuted unformly over the volume of the sold. B) The chrge wll contnuously move long the surfce, cretng constnt current. C) The chrge wll be concentrted s pont chrge t the center of the sold. D) The chrge wll be dstrbuted over the outer surfce of the sold. E) The chrge wll be dstrbuted over the outer nd nner surfces of the sold. 2. A negtve chrge = - 18 nc s plced nsde n electrclly neutrl sphercl conductng shell wth the nner rdus nd the outer rdus b. Wht chrges wll be nduced on the nner nd outer surfces of the shell? A. Inner chrge = 0 nc. Outer chrge = 0 nc B. Inner chrge = 18 nc. Outer chrge = +18 nc C. Inner chrge = +18 nc. Outer chrge = -18 nc D. Inner chrge = 0 nc. Outer chrge = +18 nc E. Inner chrge = 18 nc. Outer chrge = 0 nc 3. The sme negtve chrge = -18nC s plced on the sme conductng shell s n the problem bove, but now n extr negtve chrge of 40 nc s plced on the nner surfce of the conductor. Now wht wll the chrges be on the nner nd outer surfces of the shell fter short tme hs pssed for rerrngement? A) Inner chrge = 0 nc. Outer chrge = -40 nc B) Inner chrge = 18 nc. Outer chrge = +18 nc C) Inner chrge = +18 nc. Outer chrge = -18 nc D) Inner chrge = +18 nc. Outer chrge = - 58 nc E) Inner chrge = 18 nc. Outer chrge = 40 nc Pge 1 of 7

2 4. A pont chrge of 2.0 nno-coulombs s t the center of n (unbroken) egg-shell. Wht s the totl electrc flux through the surfce of the shell? A) 8.85 x N m 2 /C B) 226 N m 2 /C C) 0 N m 2 /C D) 9x10 9 N m 2 /C E) Answer depends on the dmeter of the egg. 5. An electron moves from pont to pont f, n the drecton of unform electrc feld. Durng ths dsplcement: f A) the feld does postve work, the potentl energy of the electron does not chnge B) the feld does postve work, the potentl energy of the electron ncreses C) the feld does negtve work, the potentl energy of the electron ncreses D) the feld does postve work, the potentl energy of the electron decreses E) the feld does negtve work, the potentl energy of the electron decreses 6. The fgure shows the electrc potentl s functon of the dstnce x. In whch regon would the mgntude of the electrc feld be the lrgest? A) Regon 1 B) Regon 2 C) Regon 3 D) Regon 4 E) Regon 5 7. Three dentcl pont chrges hve the sme chrge equl to += +2 µc. The fourth chrge hs - = - 2 µc. They re locted t the corners of the dmond s shown n the dgrm. Ech sde hs length = 2 m, wth 60 0 ngle locted s shown. Wht s the electrc potentl t pont E, the center of the dmond shpe? The potentl t nfnty s defned s the zero reference level. A) Zero olts B) 1.04 x 10 4 olts C) 2.08 x 10 4 olts D) 3.6 x 10 4 olts E) 5.68 x 10 4 olts E Pge 2 of 7

3 8. Whch of the followng sttements bout equpotentl surfces s flse: A) An equpotentl surfce cn be n mgnry surfce. B) An equpotentl surfce cn be rel, physcl surfce. C) Adjcent ponts tht hve the sme electrc potentl form n equpotentl surfce. D) The electrc feld lnes re tngent to the equpotentl surfce t the pont where the feld s mesured. E) When chrged prtcle moves from one pont to nother on the sme equpotentl surfce, the net work done s equl to zero. 9. An extremely lrge nonconductng sheet cretes equpotentl surfces, whch re plnes. The potentl dfference between every two plnes tht re 2 mm prt s 1000 volts. Wht s the surfce chrge densty σ on the sheet? A) 4.43 µc/m 2 B) 8.85 µc/m 2 C) µc/m 2 D) 4.43 nc/m 2 E) nc/m Whch of the followng sttements s flse? A) The electrc feld E nsde prllel plte cpctor s unform nd equls - / x. B) The pltes of cpctor re equpotentl surfces. C) The pltes of cpctor hve equl nd opposte chrges = C on them. D) The cpctnce mesures how much chrge must be on the pltes to produce some prtculr potentl dfference cross them. E) The cpctnce C = / depends on the potentl dfference between the pltes. 11. When cpctor s connected to 6 volt bttery, 24 µc of chrge ppers on ts negtve plte. Wht s the cpctnce of the cpctor? A).25x10 6 µf B) +144 µf C) -144 µf D) -4.0 µf E) +4.0 µf Pge 3 of 7

4 12. If the plte seprton of n solted prllel-plte cpctor s decresed to one thrd of ts orgnl vlue: A) the cpctnce s trpled B) the cpctnce remns the sme C) the cpctnce s one thrd of ts former vlue D) none of the bove E) ll of the bove 13. Four dentcl cpctors re connected n seres. In seprte crcut, three more cpctors, ll dentcl to those n the frst group, re connected n prllel. Wht s the rto of the equvlent cpctnce for the seres combnton to the equvlent cpctnce of the prllel combnton? A) 4 B) 12 C) 3/4 D) 1/12 E) 4/3 14. Ech of the three dentcl cpctors n the sketch hs cpctnce C = 1000 µf. Intlly they re unchrged. The potentl dfference suppled by the bttery s = 240 olts. When the swtch s closed, how mny Coulombs of chrge flow through the meter A untl the cpctors re fully chrged? A) 0.16 Coulombs B) 0.24 Coulombs C) 0.40 Coulombs D) 0.48 Coulombs E) 0.64 Coulombs + - C C C A 15. A network of current-crryng conductors s set up s shown n the dgrm. How mny coulombs of chrge pss through the mmeter n 1 mnute? 10 A. 4 A. A) 150 B) 900 C) 200 D) 1200 E) A. A 3 A. 5 A. 8 A. Pge 4 of 7

5 16. Two wres re mde of the sme mterl nd hve the sme length but dfferent rd. They re joned end-to-end nd potentl dfference s mntned cross the combnton. Of the followng, the quntty tht s the sme for both wres s: A) potentl dfference cross ech wre B) current nsde ech wre C) current densty nsde ech wre D) resstnce of ech wre E) electrc feld nsde ech wre 17. A wre tht wll be used n mkng n electrc heter s 3.0 m long nd 2.25 mm 2 n cross-sectonl re. It crres current of 4.5 A when 3.0 potentl dfference s ppled between ts ends. Clculte the resstvty ρ of the metl n the wre. A) 5.0 x 10-7 Ω*m B) 5.0 x 10-5 Ω*m C) 1.1 x 10-6 Ω*m D) 0.67 Ω*m E) 2.0 x Ω*m 18. A wre wth length of 1.5 m nd rdus of 0.15 m crres current of 2.0 A. The current densty s bout: A) 0.28 A/m 2 B) 0.49 A/m C) 0.89 A/m 2 D) 1.3 A/m E) 28 A/m Whch of the followng grphs depcts the current versus voltge reltonshp for devce tht obeys Ohm's Lw? A) B) C) D) E) Pge 5 of 7

6 20. If pece of wre s stretched by 3 tmes wht hppens to the resstnce (ssume tht the volume remns constnt)? A. Increses 3 tmes B. Increses 9 tmes C. Decreses 3 tmes D. Decreses 9 tmes E. Does not chnge 21. A physcs professor "mprovng" the wrng n hs house wnts to put n new crcut opertng t 120 olts tht cn hndle up to 25 lght bulbs of 60 wtts n prllel, whch would consume totl power of 1500 W. Wht s the mnmum cpcty, n Amperes, tht he should use n decdng whch knd of wre nd fuse to nstll? A) 0.5 Amps. B) 2.0 Amps. C) 10 Amps D) 15 Amps. E) 960 Amps 22. How much power s expended n 1.0 kω resstor when t s connected cross 120- voltge source? A) 0.12 kw B) 14.4 W C) 1.2 W D) W E) W 23. Fnd the equvlent resstnce of the crcut shown n the sketch below. A) 4.0 Ω B) 4.5 Ω C) 6.0 Ω D) 3.0 Ω E) 2.5 Ω 1 Ω 1 Ω R eq 5 Ω 4 Ω 1 Ω 2 Ω 2 Ω Pge 6 of 7

7 24. In the sketch, ll bulbs hve equl resstnces. The brghtness of bulbs B nd C dded together, compred wth the brghtness of bulb A, s A) four tmes s lrge B) twce s lrge. C) the sme. D) hlf s lrge. E) mpossble to tell 25. The Krchoff loop rule tells us tht A) The sum of the electrc felds round closed loop equls zero B) The sum of the currents round closed loop equls zero C) The sum of the electrc chrges round closed loop equls zero D) The sum of the emf's nd potentl dfferences round closed loop equls zero E) The sum of the resstnces round closed loop equls zero 26. A current of 2 A s flowng from pont to pont b. The potentl dfference b s A) 14 B) -8 C) -2 D) +4 E) Ω + 2 A Ω b 27. The fgure shows plstc rod of length L = 50 cm, totl postve chrge = 1 µc., nd unform chrge densty λ, lyng on n x xs. Wth = 0 t nfnty, fnd the electrc potentl (n volts) t pont P 1 on the xs, t dstnce d = 25 cm. to the left of one end of the rod. Select the closest nswer. A) zero B) 1 C) 20,000 D) 2 E) 10,000 Pge 7 of 7

8 Answers to Physcs 121 Smple Common Exm 2 Rev 2 1. D Chrge dstrbuted over the outer surfce of the sold 2. C Inner chrge = +18 nc. Outer chrge = -18 nc 3. D Inner chrge = +18 nc. Outer chrge = - 58 nc 4. B 226 N.m 2 /C 5. C the feld does negtve work, the PE ncreses 6. B Regon 2 7. C 2.08 x 104 olts 8. D The feld lnes re tngent to equpotentls surfce t the pont where the feld s mesured. 9. B 8.85 µc/m E The cpctnce C = / depends on between pltes. 11. E +4.0 µf 12. A the cpctnce s trpled 13. D 1/ A 0.16 Coulombs 15. D B current nsde ech wre 17. A 5.0 x 10-7 Ω*m 18. E 28 A/m C strght lne, postve slope 20. B ncreses 9 tmes 21. D 15 Amps 22. B 14.4 Wtts 23. E 2.5 Ω 24. D hlf s lrge 25. D The sum of potentl dfferences round closed loop equls zero 26. B C 20,000 Pge 8 of 7