Physics 222 Midterm, Form: A

Transcription

1 Pysis 222 Mitrm, Form: A Nm: Dt: Hr r som usul onstnts. 1 4πɛ 0 = Nm 2 /C 2 µ0 4π = tsl s/c = C Qustions 1 5: A ipol onsistin o two r point-lik prtils wit q = 1 µc, sprt y istn o m is sown low. T mnitu o t ltri il t istn r rom r prtil is E = 1 4πɛ 0 q r 2 T mnitu o t ltri il t lotion on t xis o ipol, r rom t ipol t istn r rom t ntr o t ipol tt is mu rtr tn s, is E = 1 2qs 4πɛ 0 r 3 T mnitu o t ltri il t lotion lon prpniulr istor o ipol, r rom t ipol t istn r rom t ntr o t ipol, is 1. Wt is t irtion o t ltri il t t point P 1? 2. Wt is t irtion o t ltri il t t point P 2? E = 1 qs 4πɛ 0 r 3 Us ts rrows low to init irtions o vtors. 3. Wt is t irtion o t ipol momnt? 1

2 4. [7] Wt is t ltri il t t mipoint o t ipol, t point xtly in twn t two prtils? 0 < , 0, 0 > N/C < 2000, 0, 0 > N/C < 8000, 0, 0 > N/C orrt nswr not list < , 0, 0 > N/C 5. Suppos t ltri il t point P 1 is E 1 n suppos tt t istn r rom t ipol to P 1 is mu rtr tn t wit o t ipol s. I you oul t istn r rom t mipoint o t ipol to t point P 1, tn t ltri il t tt point will E1 E1 /2 E1 /4 E1 /8 E1 /16 Qustions 6 9: Oppositly r prlll plts r rrn s sown low. An ltron ntrs t rion twn t plts wit sp v. Tis is ssntilly wt CRT (to ry tu) in TV sts n monitors uss to lt ltrons. T or on r prtil t rtin lotion in n ltri il is F = q E 6. As t ltron movs rom point 1 to point 2, it mintins onstnt sp. slows own. sps up. 7. I t potntil irn twn t plts is 120 V n i ty r sprt y 0.05 m, wt is t mnitu o t ltri il twn tm? 0.3 N/C N/C 6 N/C 2400 N/C 8. Wt is t mnitu o t or o t plts on n ltron t ny lotion twn t plts? N 6 N N N 9. Wt is t irtion o t or o t plts on n ltron t ny lotion twn t plts? lwys tnnt to its pt lwys prpniulr to its pt upwr towr t positiv plt ownwr towr t ntiv plt In nrl, t potntil irn twn two lotions in n ltri il is V = P 2 P 1 E l T intrl n vlut lon ny pt us it ivs t sm rsults. In otr wors, t potntil irn twn two points only pns on t strtin point n t inis point, n not t pt in twn. T intrl rtly simpliis or uniorm ltri il to V = E l = (E x x + E y y + E z z) 2

3 10. A ntivly r sok is rout nr nutrlly r sirt. T sok n sirt will 11. rpl. ttrt. not intrt sin r ojts n nutrl ojts o not intrt ltrilly. Two initilly unr onutors, 1 n 2, r mount on insultin stns n r in ontt, s sown ov. A ntivly r ro is rout nr ut os not tou tm. Wit t ro l in pl, onutor 2 is mov to t rit y pusin its stn, so tt t onutors r sprt. Wi o t ollowin is now tru o onutor 2? It is unr It is ntivly r. It is positivly r. It is r, ut its sin nnot prit. It is t t sm potntil tt it ws or t r ro ws rout nr. 12. For tis typ o mtril, ny xss r prtils must on t sur o t ojt. insultor onutor ot n insultor n onutor nitr n insultor nor onutor 14. For tis typ o mtril, vln ltrons r moil, n w tink o tm olltivly s s o ltrons. In t prsn o n ltri il (u to xtrnl r prtils o ours), tis s o ltrons will istriut itsl roun t sur so tt it prous n ltri il vrywr insi t mtril tt ountrts t ppli ltri il (u to xtrnl r prtils). T nt ltri il witin t mtril is tror zro. insultor onutor ot n insultor n onutor nitr n insultor nor onutor 15. I tis typ o mtril is sp lik spr n s xss r prtils, t ltri il u to t spr t points outsi t spr is t sm s i it wr r point prtil t its ntr. insultor onutor ot n insultor n onutor nitr n insultor nor onutor 16. Suppos r pi o Sot tp s nt r o Q = C. How mny xss ltrons is tis? 1 ltron ltrons ltrons ltrons ltrons 13. For tis typ o mtril, ltrons r not moil; tus n xtrnl il uss toms in t mtril to om polriz. Tror, tr n non-zro nt ltri il witin t mtril. insultor onutor ot n insultor n onutor nitr n insultor nor onutor 3

4 Qustions 17 20: A yron tom (nutrlly r o ours) is nr two r prtils s sown low. 17. Wt is t irtion o t nt or on t yron tom? T mnitu o t or o r prtil wit r q on nutrl tom is 18. Wi iur low is t most usul mol or pitin t polriztion o t yron tom? F = ( 1 4πɛ 0 ) 2 ( 2αq2 r 5 ) T or is u to t t tt t r prtils rt n ltri il t t lotion o t nutrl tom. Tis ltri il polrizs t tom, sitin its ltron lou su tt t nutrl tom ts lik ipol wit ipol momnt p. T inu ipol momnt o t tom is irtly proportionl to t ltri il t t lotion o t tom. T proportionlity onstnt is ll t polrizility α. 4

5 19. Wt is t irtion o t inu ipol momnt o t yron tom? 20. T polrizility o yron is out Cm 2 /V. T polrizility o ron is out Cm 2 /V. I t mnitu o t or o prtil on t yron tom is F, wt woul t mnitu o t or o prtil on ron tom i it ws t t sm lotion s t yron tom? 0.37F 0.14F F 2.7F 7.3F 5

6 Qustions 21 24: An ltron m is us in to ry tu (CRT) to mk t otin on srn low. T r o n ltron is C, n its mss is out k. Suppos tt ltrons r lrt y rion o uniorm ltri il. T ltrons ntr trou smll ol in pitor plt n xit trou smll ol in t otr pitor plt s sown in t iur low. 22. Wt is t irtion o t ltri il twn t plts? T potntil nry o systm wit r prtil o r q t lotion wit potntil V is U = qv T kinti nry o t ltron is K = 1 2 mv2 T systm is los systm, tus t nry o t systm is onsrv (t nry prinipl!). 23. At wi plt is t potntil t rtst? t positiv plt t ntiv plt nitr, us t potntil t t lotion o plt is t sm 24. At wi o t points sown in t iur low is t mnitu o t ltri il t rtst? 21. [7] I t sp o n ltron ntrin t plt is m/s wt soul t potntil irn V ross t plts in orr or t sp o t ltron to 0.1 wn xitin t plts? T onstnt is t sp o lit, m/s volts volts volts 2230 volts 2250 volts P 1 P 2 P 3 Non o t ov us t ltri il is qul t ll tr points. 6

7 Qustions 25 28: Currnt lows trou loop o wir tt is onnt to ttry. T pln o t loop is lin wit t nort-sout irtion, n ompss is l t t ntr o t loop. (S t iur low.) T rius o t loop is 0.02 m, n t nl is lt 30 rom nort s sown. T orizontl omponnt o t rt s mnti il is out T t our ltitu. T mnti il t lotions lon t z-xis o loop o urrnt-rryin wir is B loop = µ0 4π 2πR 2 I (z 2 +R 2 ) 3/2 25. In wt irtion is urrnt lowin roun t loop? ountrlokwis lokwis urrnt is not lowin in t loop, so I = Wt is t mnitu o t mnti il t t ntr o t loop prou y t urrnt in t wir? tsl tsl tsl tsl 27. [7] Wt is t urrnt in t wir? mpr 0.38 mpr 0.54 mpr mpr 28. MRI (mnti rsonn imin) mins us lr oil o wir to nrt lr mnti il witin t oil. Suppos tt t mnitu o t mnti il t t ntr o oil o rius R us in n MRI min is B. I t MRI oil n trt s tin oil, wt woul t mnitu o t mnti il t istn 2R rom t ntr o t loop, lon t +z xis? B/2 B/4 B/8 B/4 3/2 B/5 3/2 29. A positivly r prtil movs wit t vloity sown in t iur low. (Mttr & Intrtions Cy n Srwoo) Wt is t irtion o t mnti il t point 5? +x x +y y +z z non o t ov 7

8 Answr Ky or Exm A