1e3test2-2005-solutions - PHYSICS 1E03 TEST March 14, 2005...

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Unformatted text preview: PHYSICS 1E03 TEST March 14, 2005 Name Ed l 54 Q3“ ‘5‘: Instructors: Student Number A. Jopko (section C01) N. McKay (sections C02, C03) Mac email: @mcmaster.ca D. Venus (section C04) K. Sills (section C05) Instructor: Write your name and student number on your paper before you begin. Multiple-choice questions are worth 2 marks each (only the answer is marked), and problems are worth 3 marks each (clear solutions required). Only the McMaster standard calculator (Casio fi-991 ) is allowed. Notes and formula sheets are not permitted. Some formulae are given below; if you use them it is your responsibility to know what they mean and when they can be used. Earth’s gravitational field: g = 9.81 Inst Electronic charge: 6 = l.60><10‘l9 C Electron mass: me = 9.11x10'3l kg Proton mass: rm1 = 1.6Tr'><10_21 kg Coulomb’s Law constant: it. = 8.99x109 N-m’rc2 Permeability ofvacuum: tr, = 411x 10‘1 T-mz-A'l Permittivity of vacuum: so = (4rd:e )'1 = 8.85MB"l2 Cz-th-rn’2 2 1 F=ma 0,2:— J=§=nqu=05 Rsedes=Rl+R2+m r K:%mv2 p=lf0t R;;fllc,:Rfl+R§l+-u pL U:*WCO”"=—-IF'dr lie—:7 CWBIZC1+C2+'H F=qE V=IR 03m =01"l +C;’ +--. Ezke—i-i‘ q(r)=Qoe—f/RC r - -1 _ _ ( 4330) (DE "4E.dA“;_‘-Qenc '4nkeQenc 9(0—Qfinal 1—8 0 CF #0 I‘dst : =——=27dc F: B dB=—— plane E 280 err qvx I 4” r2 conductor: E=i=47dfea F=IL><B tj‘BIdEauolmww 5'0 [Jqu de—Eods r:1AxB:;1xB straightwire: 82:0; :rr q . Q -. « V=k - (j. 2—— solenotd. B~ :11 gr AV #0 A -1 2 u _ C—Kgfld 1——9 10 11 12 13 Total (18) Q) £3) £2) (31 (30 continued on page 2... Page 2 of 8 pages Part A (multiple choice): Print the letter corresponding to the best or most nearly correct answer in the box beside each question. Each correct answer is worth 2 marks. 1. A fuse “blows” if the current exceeds 1.0 A. It is made of a material that melts at a current density of 300 A/cmz, What is the diameter of the wire in the fuse? A) 0.98 mm :9», __ ’1: “L B) 0mm (“JP n/éawz if I ‘ o enoug Information. Need to know the length of the Fuse wire. answer C. 2. The resistance between points A and B is A)R i . £93,212 ‘1 2% V2 answer R D 3. A rectangular loop of wire in the x-y plane carries a current I flowing clockwise as shown. The loop is in a region of non—uniform magnetic field 131:10'5 yj T, where y is measured in metres. The net magnetic force on the loop is ",-..-.-- ‘ —. . /I-‘——w ' -I.. .n... _. - "_ 5‘ z A} parallel to the z axis..._3t “parallel to the x axis C) parallel to the y axis D) zero. y . answer ' i":- i 4 J i” i q.__ x I continued on next page... Page 3 of 8 pages 4. A capacitor with a dielectric slab between its plates is charged by attaching it to a battery. In order to end up with the largest potential difference across the capacitor, it is best to A)....first.rsn10_ve the dielestris #399. battery 4""Bufflatsconfiééfthé‘Haitérmhcumofithscdislsstris.4A ‘ “5) Either give the same result in the end. answer 5. What fraction of the current I passes through the resistor “r”? -1 I I" R @fljflrwfifi ~- ,, a . .,. ___. CB?) Melvin V t I»; Q ’ 1w " I r ‘ (A D) R l' - n... 2.» g; _ a»? -. e ' ... l a, r f R answer 3 6. What is the time constant 1: for this circuit? C é)__J.f.6_ _RC R S? (:2 my? 8 :T J, 0 WW C answer '13 continued on next page... Page 4 of8 pages 7. A straight wire carries a 3.0 A current along the xuaxis in a magnetic field B=0.30i +0.90j T. If the wire experiences a magnetic force of2.3 N, how long is the wire?“ A 2.6 m 41. _, : .. I“ . k, f ’B) .... 1 1-} it}. : , 7? , r', ,{W 3; "0) 0.31m ‘ D) 0.64m [:7 :3?- ’33? k1 BHSWCI' '73 8. An cat-particle (2 protons and 2 neutrons bound together) has a mass of 6.6235(10'27 kg and moves in a circle of radius 5.0 cm in a uniform magnetic field with strength 0.03 T. What is the acceleration of the particle? 0h» _ . 4 frat if” '— “* Vt -. 1L5 ‘- a...’ A) 0 B) 9.8 HUS: 2 2 53 :3- I” C) .IIUIS-_H_ pm I" W 9”“ i l :7 §.a Hf} {p @Toztxlo” mlsz “a, W vi: " it *1“ n... r finwwmwnwo—fl" W Answer D 9. Before the switch is closed, the capacitor has no charge on it. The instant after the switch is closed, the current I is R1 A) 0 B)_ 81'(R1+R3) + 5 _ C R2 mama) l ! {—-—.—— Answer I (3. continued on next page... Page 5 of 8 pages Part B (Problems): Write a clear solution showing how the anSWer is obtained. Each problem is worth 3 marks. 10. A square rod and a cylindrical rod are made of the same copper alloy and cut to the same length, as shown in the diagram. When a potential difference of 1.70 V is applied across the length of the L cylindrical rod, it dissipates 10.0 W by 28 I L Joule heating. What voltage should be applied across the length of the square rod so that it also dissipates 10.0 W? 23 Z T3 -~ T \i t V J P "‘ L» answer /. ‘5) gab/5- continued on next page... Page 6 0f 8 pages I 1. Two very long wires carry equal currents of3.5 A into the page in the diagram. The wires are at positions x = ~d and x = +d on the x~axis. Find the magnitude and direction ofthe magnetic field at the position y = +d on the y»axis when d = 7’ em. I _...,‘ a? “E 1. , <1: i “ EJ4§° RX, E. 7:} ix) ; f; ‘i "6 i' ‘r. W b H ; . x ' . _ j 1. 2 1 «2 r1 answer Magnitude: /(). 0 A, T ’1 Direction: 7 {fa-f "’9 continued on next page”. 12. Find the current 1;, when R=189 and 8:9.0 V. Include correct sign for direction defined in the diagram. Li’mli‘ér 9 3* I i T iU'E‘ia C. or r 4 "2"" .e g t 3.1 . 36‘” 1 L +- 29 13 level? :2 (vie/.1 ‘ __.. 19(- _.. ,_ m r - .... *2 -3 2 a? 3.1 “£8.13” D¢©l€sefiéij' #:311731qu 1:”; Page 7 0f8' pages ("i "x .. {‘f j 2/ 33 ‘ 5’ “400wA if at 7" 4 I’m} "’9’ ~I.“ F131 f3 : ~— 3.100 wage answer we Boowfi} continued on next page... “1):: 114‘ '. Page 8 of8 pages 13. Use Ampere’s Law to find an expression for the magnitude of the magnetic field at any radius r inside a cylindrical wire of radius R. The wire carries a current, with the current density J uniform across the cross-section ofthe wire. Show the path along which you apply Amperc’s Law, and provide explanations for why you have chosen this path. ansWer RIMS" Eli/(“7" END ...
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1e3test2-2005-solutions - PHYSICS 1E03 TEST March 14, 2005...

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