Practice Exam 3_B solutions

# Practice Exam 3_B solutions - EMW‘ Hi 3 ”Fem j W W97_H...

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Unformatted text preview: EMW‘ Hi 3 ”Fem j. W W97 /__________H_____. l. The diagram shows three equally spaced wires that are perpendicular to the page. The currents are all equal, with #l and #3 being out of the page and #2 being into the page. Rank the wires according to the magnitudes of the magnetic forces on them, from least to greatest. Cl TH». a l\ A) 321 Bisaaimﬁi BED BﬁMQWéﬁ: ld‘ can . t1e,t e11] E) l and 3 tie, then 2 2. Two long straight wires enter a room through a window. One carries a current of 3.0 A into the room while the other carries a current of 5.0 A out. The magnitude of the path integral (if?- d! in T m around the outer edge of the window 13: A) 6.3 x 10 6 3/?) B) 10x10— 1 J3 51?: :ha/M W: #615 CL 3.8 x 10’ 7 W x2 x”) X2) E) none of these 3. In the lecture demonstration shown below we had two solenoids. The solenoid on the right. connected to the ammctcr, G, can be fixed at different positions with respect to the solenoid on the left. Which of the following statements is/are correct? {NP-’7" U14; J! _.-———-v There is a current in G just after S is opened or closed. f I ,__,__, The magnitude of any current in G depends on the relative position of the solenoids ”A I The direction of any current in G will always be the same F: There is a steady deflection (current) in G as long as S is closed _____ .The deﬂection of G can be increased by inserting an iron bar inside the left solenoid / “-7 A) 2and3 B) 2,4,and5 1%; D) l, ’3, and 5. E) l and 4 Version I Page I 4. The primary of a 3:1 step~up transformer is connected to an AC power source and the secondary is connected to a resistor R. The power dissipated by R in this situation is P. [f R is connected directly to the source it will dissipate a power of: A)PB a, t g; :13 \ém ~ EVWm/a/ DLQP OJ/ PM“; W :- #W’ﬂpma 5. Two very wide conducting sheets carry current into the page in the edge View below. The current in the sheet per meter of horizontal width is it (in Amps/m). The magnitude and direction of the magnetic ﬁeld at points P, Q, and R are. respectively: T a ~O”P—-—>— a ﬁll BFQ ZﬂQA/Q. 6. The diagrams show three circuits consisting of concentric Circular arcs of radii 1‘, 21", or 3r connected by radial segments. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest. Version I Page 2 ;~¢0d> é ﬁre-Wwéfﬁo 7. A rectangular loop of wire is plaCcd perpendicular to a uniform magnetic ﬁeld and then spun around one of its sides at frequencyf. The induced emf is a maximum when: A) none of the statements is correct B e d rivative of the magnetic ﬂux with respect to time is zero C) the magnetic ﬂux is zero 1)) the magnetic flux is alf its maximum value E) the magnetic flux is a maximum 8. A rod with resistance R lies across frictionless conducting rails in a constant uniform magnetic ﬁeld B, as shown. Assume the rails have negligible resistance. The rate at which work must be done by a persou to pull the rod to the right at constant speed v is: lemm— 2: Mt WW 27 p Zeus f A 2 2) B; 5mm )2 C) BZva/R E) BEL2v2/R " 9. 1n the circuit shown below the switch has been closed for a long time. Immediately after opening the switch what is the rate (in Joules/s) at which energy stored in the inductor. L, is decreasing? 3 9) . 17 at: are) 1 tans” 6; s z; WWW-3373” P: team a W W Versionl Page3 0—1 375 10. As a loop of wire with a resistance of '10 9 moves in a constant nan—uniform magnetic ﬁeld, it loses kinetic energy at a steady rate of4 mJ/s (milli-Joulesls). The induced current in the loop: A) is 7 mA W WM?” MAI “”0311? B)__ is 2 8_r_nA C) is ED mK “ 5 cannot e cale ulaled from the given data C 13/2 ﬁlx/D E) is 0 -—Z i -. 17¢ / D A 11. The capacitor C is initially charged. After the switch .is closed which statement is true about the current in the Circuit? C) 1 It always has damped oscillation with (1)2 TC It always has damped oscillation with (0- f—% 2 )9’5) "§@t does not have damped oscillation if R_ > 2f '12. A resistor. inductor, and a switch are connected in series with a battery The inductor is a solenoid. When 'olgnoid is filled with amaterial it is observed after the switch is closed, that the ent builds up ust a little bit faster han it does without the material in W gt) diamagnetic R W ) uranium \\ " C) paramagnetic \-.\ W M a ,. D) a superconductor \ 8 ~ ' ' 4/3 W E) ferromagnetic - __ 1m ' ' ﬂ Version 1 Page4 13. The diagram shows an inductor that is part of a circuit. The direction of the emf induced in the inductor is indicated. Which of the following is possible? ‘ SIP—'3' \$123 _W) M A) The current is to the right and decreasing W m B) T ecurren.is .ot e exan creasmg C) The current is to the right and constant ,5) 2 VA W D) The current is to the right and increasing _ E) The current is to the left and constant To - - 14. The solid circle of radius R in the diagram shows the top plate of a parallel—plate capacitor. The dashed circles are t our integration paths have radii of r. : R/4, r2 : R/2, r3 2:3 13/2, and r4 : 2R. Rank the paths according to the magnitude of the circulation, (i é-dl‘, around the paths during the discharging of the capacitor, least to greatest. ’3" ,5 g, ............ amt/1 2t 9 A) 1, then 2 and 4 tie. then 3 \ WﬁZ B)4,3,1.2 (“D J C ll t' -‘ ##ﬂ‘“ ' :3ng Bfi’ﬁéfs and 4. tie M 30,4;th W 15. An oscillating emf of variable frequency f and constant amplitude an is applied to a solenoid of negligible resistance. The magnetic energy density for any point inside the solenoid: ~\ .\ EA) @i L— D) oscillates and has amplitude proportional to 1/f 7... E) oscillates and has amplitude proportional to f2 2. E} 2. r" _ a, m ———-—- 2 “MB 5&0»cm 2%“ U) 1C Version I Page 5 l w M > Lo 16 A capacitor in an LC oscillator is observed to have a maximum potential difference of 15 V and a maximum stored energy of 3 60 la]. At a certain instant the energy stored in the capacitor is 40 it! At that instant what 1 the magnitude of the emf induced in the inductor? A) '15 V B 20V C 5V D) 8V VCZC. 3c?) 2’; W E) zero :; WW 1 :2 ) it ”‘3 a, [it E E1: Va; UL, 30 H ﬂ> gm 3,1523”? 17. A certain region in space contains no currents. It is found that the magnetic field in the region is up and increases in magnitude as you move to the right. To be consistent with Maxwell‘s equations we must conclude: \A - I- """""" ) There must be a changmg elcetnc ﬁeld w1th dE/a’t pomting into the page Qhere must be a changing electric ﬁeld with dE/dr pointing out of the page There must be a constant elecu 1c held E pointing into the page D) There must be a uniform electi 1c tie Id pointing down in the opposite diiection to B E) There must be a constant electric ﬁeld E pointing to the light /zp\, 18. An oscillating emf of (S (t) = .] SOVCOSB What is the RMS current in this circuit? gtﬁs connected to a capacitor with C = 10 ttF. 33 3-2: I”: is; éme1Q501577ﬁo"):4567A D) a "_”“ ._ E.) 0,57A LEN/13p Version 1 Page 6 19. A wire of finite length L carries current I out along the Xmaxis. What is the magnitude of the magnetic ﬁeld at point P a distance R from one end of the wire as shown in the diagram. A) JuOIRL dx (7 - Wiltxﬁal) Tame/1 Bret/80M WW 4 l 2 2312 1:0(x +R) L C) #0153]- xdx if? r .2 R2 U” (l + l 2.. l L D) #01}? ”f dx P :— )K +1? 42: 7m(x2+R2) 20. Imagine a square sheet of copper suspended from the ceiling as a pendulum. We ﬁrst move a permanent dipole magnet directly in towards one face of the sheet. and then move the magnet back out away from the sheet. Describe the general motion of the sheet A) the sheet is attracted as the magnet moves in and attracted as the magnet moves out B the sheet is attracted as the magnet moves in and repelled as the magnet moves Out the sheet is repelled as the magnet moves in and attracted as the magnet moves out D) the sheet experiences no forces from the. moving magnet E) the sheet is repelled as the magnet moves in and repelled as the magnet moves out was 2W aeMWW ﬂee Version l Page 7 ...
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