April_2007_Exam3_and_solutions

April_2007_Exam3_and_solutions - Name 50/0 £l‘oflé ECE...

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Unformatted text preview: Name 50/0 £l‘oflé ECE 311 Exam 3 Spring 2007 April 12, 2007 Closed Text and Notes 1) Be sure you have 15 pages. 2) Write only on the question sheets. Show all your work. If you need more room for a particular problem, use the reverse side of the same page. 3) Write neatly, if your writing is illegible then print. 4) The last 5 pages contain equations that may be of use to you. 5) This exam is worth 100 points. 3 (5 pts) 1. Two thin parallel wires carry current along the same direction. The force experienced by one wire due to the other is A) parallel to the lines perpendicular to the lines and attractive. C) perpendicular to the lines and repulsive. D) zero. B (5 pts) 2. For static fields, I E ° dl is independent of the path A A) only if E is spatially uniform. B) only if E has spherical symmetry. C) only if E is due to a uniform line charge. always. (5 pts). 3. The Curie temperature is the temperature where A) iron melts. ferromagnetic material looses its ferromagnetic properties. C) a diamagnetic material becomes a paramagnetic material. D) a changing magnetic field no longer produces a current in a metal. (5 pts) 4. The magnetization field saturates in a ferromagnetic material because ll the atomic dipoles are already aligned to the applied magnetic field. B) thermal energy in the material does not allow any more alignment of the atomic dipoles. C) of a limit on the size of the applied field. D) an internal field is generated to oppose the applied field. 4 (10 pts) 5. A conducting loop of total resistance 5 S2 and inner area 1 m2 is in the xy—plane. The magnetic . . Wb . . . . . . flux densrty 13 B = 0.2t a2 —2 What IS the current flowmg 1n the loop? What is the dlrection m of the current? W L) - ~ ¢:j§n;g: (0,;1‘6 0.02:5 WA _ Gig. _ - 51969419 W53: :2 may Vemr ‘ 4+ ' At lvemll (121/ (I): ~ ______ : IQ ’ 51L The Cul‘l‘fmi“ will fifné’fdllf’ or E {me/fl £0 affoée “EA/e Cache/{94 [A (2 LR (L45: az Jk‘rqfibfl $0 T MEN 5954 #46 ‘9¢ JC/‘Fcfi‘em Q’- (10 pts) 6. A charged particle of mass 4.644x10_26 kg and charge 1.6)(10—19 C is moving at a speed of 2.62x104 m/s. The particle enters a uniform magnetic field and starts moving in a circle with radius 0.076 m. What is the magnitude of the magnetic flux density? ,J I) 4 MH1 k 'L MU @MB: ~— Vé lit/i, I 77; ML S (10 pts) 7. Determine the inductance per unit length for the N turn tightly wound solenoid shown of cross— J sectional area S and length 5. a ~ “ " J, ____:~__:;» “ \ , V _flflfirfinfiflfiflr ~4réts,“ - m: l l lit. A > »' v - l' ll. WI 7 ‘1 ll}? 2' ’ > i 3‘ r qt “a 'l . w.’ ’1‘ “ ’1‘- "= "~:' 4_‘ 5‘ ‘ Wing 5 Is‘ ii u 5. :~.' *g' l: J ' If 'a '1 ’ a ‘3 la i s 5' a Vvll W [feed “60 {LBJ f/m Mdymr‘h‘c jq‘la/o/ [4960(1’ {14: Coil, HID/3’71 “Myth?wa CCPCuC‘tql MW {‘30 l’l’he 9U! 46% “1L .J d (J '3‘ ‘4).4 "A 9 f:\(élJ‘Wl\(H‘M+ind(/+Ifl #M A lo C —_-\ t \- TAQ WM 59 wmk 10mm C770] 6M} H L$ figm‘fiq/Z/ go Jew/i xS Heal? :va ‘ A a x g‘ $9 H muet Le (009'le 1‘ C" 95”” five an MC Magi Le HM gamma w g0 emf.“ rive agl £0) fay/V1 6 (10 pts) 8. A current of 1 A is flowrng 1n the av) directlon in a wrre loop of cross—section area 1 m that IS in the xy-plane and centered at the origin. What is the torque on the wire loop if there is a uniform magnetic field of B = lOgaX ? m in .A l 4 I A 7“ >1§3A1 (ii/“(1m a2: flm 43 71.; w. 7 (10 pts) 9. Two rails have negligible resistance and attached to the rails is a voltage source and resistor, as shown. A 0.1 kg metal bar of negligible resistance is laid across the rails and is free to move. Wb Everywhere there is a magnetic flux density of B = 10—-—2-az. What is the force on the bar? m m 8 (10 pts) 10. A conducting rod of length 2 m is in the xy plane with one end fixed at the origin and rotating about the z—axis with an angular velocity of 2 radians/s. If there is a uniform magnetlc field of B = USE/galz what voltage develops across the rod? m To? form» an (‘41: e/écffonc (A t/w fog! [c E2~3Y§ /\ Q:W§a¢ 90) A 95-521 ma 2% E: 23’ Cm). 02'” A W A ‘3 /\ V~ _fE.Jj:-j(_p.9wfide\¢d)€afi “:3: 0 2M 3"“ W19 ng WA, \/:j [OS—WEdCDI/Ml ""f‘€ “T; O 0 l/ : ICU WE 10H? 913‘“ Wt) V6, 9 (5 pts) 11. A sheet current density of K = 63y A 's flowing in the xy plane. If the magnetic field intensity m for z > 0 is H = 2ax +1ay + 3azfi, what is the magnetic field intensity for z< O? The relative m permeability is the same for z > 0 and z < 0. B 1 B 21, 10 (5 pts) 12. Flux linkage is @he number of turns in a coil times the magnetic flux through the coils B) the ratio of electric flux to magnetic flux C) a term to refer to the flux between two circuits. D) the ratio of magnetic flux to current causing the flux. (10 pts) 13. Indicate whether the following statements are true or false. l l_ _ The magnetization, M, is the magnetic dipole moment per unit volume. @ False Energy cannot be stored in an inductor. True In a uniform magnetic field, a magnetic dipole will rotate to point in the False same direction as the magnetic field. Electric field lines always begin on positive charge and terminate on negative charge. Displacement current is caused by a changing electric field True False ...
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April_2007_Exam3_and_solutions - Name 50/0 £l‘oflé ECE...

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