Practice%20Exam%203_A%20solutions

Practice%20Exam%203_A%20solutions - Est/w 3 2 Poem L 1. In...

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Unformatted text preview: Est/w 3 2 Poem L 1. In the figure, the current element idl, the point P, and the three vectors (1, 2, 3) are all in the plane of the page. At point P the direction of the vector dB, due to this current element, is: A) in the direction marked "3" B) in the direction marked "1" C) out of the 6 IX} into the page ) E) in the direction marked "2" 2. A 45-mH inductor is connected to an ac source of emf with a frequency of 400 Hz and a rms voltage of 20 V. The RMS current is: A) 2300 A t B) 360A ’“ E 20 \/ , - fig/fl“ C)0 LRMS ,jl‘A. D . . X ' airway/.mer @ L- (of: :— (2/8 A 3. In an ideal 1:8 step.@ansformer, the primary power is 10 kW and the secondary 25 A. The pnmary voltage is therefore: : n V 3 IOQZESA/fi C) 6.25 v g D) 400 v \l/ E) 25,600 v Page 1 4. Four long stra' ;- ' es carry equal currents into the page as shown. The direction of the magneti xerted on wire F is: \ 7Q w —fll— E v70 BM Er 5 FZLIZXBZQIenT<E) ‘3’ B) west C) north D) zero E) south 5. A hollow cylindrical conductor (inner radius 2 a, outer radius 2 19) carries a current i uniformly spread over its cross—section (shaded). Which graph below correctly gives the magnitude of B as a function of the distance r from the center of the cylinder? Page 2 6. A uniform magnetic field of 1.0 T is perpendicular to the plane of a wire loop of area = lmz. The wire has negligible resistance but there is a 2.0 Ohm resister in the loop. If you simply flip the loop over 180° the total charge that flows through the resistor in this process is: t A)0.20C arr—44> :; (,Rz Mfg 2i iogc 3; ~ « _. /d’t _.., ,_ ~2C 7r R 2:1. 7. A long straight wire is in the plane of a rectangular conducting loop. The straight wire carries a constant current i, as shown. The rectangle is first moved closer to the wire, then slid upwards parallel to the wire, then moved back outwards from the wire. During these movements the current direction(s) in the rectangle is/are: eclomtsmr : WufilNJ TM I 6 :0 ’ 4:412, we» ' g % MU} A) counterclockwise, zero, counterclockwise B) clockwise, zero, counterclockwise C) 2 r0 zero D) counterclockwise, zero, clockwise E) c 0c Wise, zero, clockwise 8. A rod lies across frictionless rails in a uniform magnetic field B, as shown. The rod is moved to the right with constant speed v. In order for the emf around the circuit to be zero, the magnitude of the magnetic field should: I ""“‘”‘““*~X Q3 ' A ' z r B dds " 55:43’69’9 Afit 7,!” aidecrease linearly with ti “ad: 7 B) not change C) increase quadratically with time D) decrease quadratically with time E) increase linearly with time Page 3 9. A current of 10 A in a certain inductor results in a stored energy of 40 J. When the current is changed to 5 A in the opposite direction, the stored energy changes by: M60] u; ,‘LLIL: Lilo—J— “MAI-um}; B) 20] w: ’/ isle—$2M mt: 30:1“ 10. A copper penny slides on a horizontal frictionless table. There is a square region of constant uniform magnetic field perpendicular to the table, as shown. Which graph correctly shows the speed v of the penny as a function of time I as it passes through the region? topview a '3' IE! '8' I3 131 t? .3) o®®®®fio_) e a a o3 '8 ® fl *5 ® 12' GI W r I t I II III II 1' r f N V A) I B) 11 C II E) V I]. A flat coil of wire, having 50 turns, has an inductance of 2M1 and resistance of 1.0 Ohms. The inductance of a similar—area coil having 200 turns but onl twice the A emstance 15 In uH: kg N51: > CH 1 L r: @921 I a UN {30 Ls») é’ Law: 32%“ Page 4 12. An inductance L, resistance R, and ideal battery of emf a; are wired in series. A switch in the circuit is closed at time 0, at which time the current is zero. At any later time I the potential difference across the inductor is given by: A) _ e—RH'L) B) _ ethi’R) C) (fie—LIFE 9) 4m V :- = .R/_ i|1+e ) L_ d1: 13. A square loop of wire moves with a constant speed v from a field-free region into a region of uniform B field, as shown. Which of the five graphs correctly shows the induced current i in the loop as a function of time t? (positive i is CCW) 961965? @Gfifl @E‘Qfiifi F“ @936 [:I—eveeeee; @QQB‘ fififlfifi‘? @fi'flfi ®E®®® 1’ 1' i I I I D E A)A EJE Page 5 18. Coils P and Q each have a large number of turns of insulated wire. When switch S is closed, ammeter G briefly reads negative current. With 5 still closed, to make the ammeter G briefly read positive one could: A) move coil P toward coil Q B) move coil Q toward coil P C) quickly increase the battery voltage in ve the slide of the variable R quickly to the right (lower R) E) none of these will wor f is connected to a parallel plate capacitor. The magnetic 19. A sinusoidally oscillating field between the plates i . a sinusoidal in time and i amplitude does not depend on the frequency of the source inusoidal in time and it amplitude is proportional to the frequency of the source ) constant D) sinusoidal in time and its amplitude is inversely preportional to the frequency of the source E) 0, since the capacitor voltage is ‘90" out of phase with the current 20. An LC circuit has a capacitance of 30 ,UF and an inductance of 15 ml-I. At a given instant the charge on the capacitor is known to be 10 MC and the current is 20 mA. The ~ {mum charge that one would observe on this cit-pacimr is thereftgre: L I .. I l ' .— “I”; uc- 3% L2 (0 J .. LEI/1 B) 8.9,“: '2 _ C)10,uC 3‘HD) ‘ _ 7. [El iii ’l/LL: ’le LL-T— QZIfiISflXZX/fia = 3D/J ._ " 'L 7Jim; 7'7)“; 92,322“ a fps, =- l7/l C 14. Let's imagine that scientists working with a new form of matter can enerate a ma etic field B that ‘ arallel to the x axis wi I Which, if any 0 Maxwell's laws w1 we nee to change? ; axwe 5 equations won't change auss' law for magnetism and Faraday's law 5 E: J; % O '37 MNOPOLE‘S Gauss' law for magnetism and Ampere's law EN“ 51— D) Faraday‘s law only \U/ E) Ampere's law only FhRPt I)th mw magnetic field produced by the magnetic dipoles of the paramagnetic substance is: A greater than BU and in the same direction ( bss than Hg and in the same direction ) less than Bo and in the opposite direction D) the same as Bo E) greater than Bo and in the opposite direction 16. An very wide sheet of uniform, constant current density, J, has thickness of 221. J points straight out of the page. What is the magnitude of the magnetic field a distance y (y<a) from the mid lane of the sheet? P 4*— L——> m 7/31?” 0 a?” ” 375% D) 3%?» E) #UJa 1?. A 0.70m radius cylindrical region contains a uniform electric field that is parallel to the axis and is increasing at the rate 5.0 x 10'2 Vim - s. The magnetic field at a point 0.25 m f In the axis has a magnitude of: dam-- B) 2.8 x10“ T C) 5.4x10‘5T .a- A“ D) 10x10—5T E)0 ...
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Practice%20Exam%203_A%20solutions - Est/w 3 2 Poem L 1. In...

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