# Practice Exam 2 Winter 2006

## Physics 126 with Riles at University of Michigan - Ann Arbor *

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* University of Michigan Physics 126 Winter 2006 Practice Exam2 Useful Physical Constants: e -l .602x 10-1e C so = 8.85x1 0-12 C', (N.m2) k -Ll(4neJ = 8.99x10e N'm2 /C2 g =9.8 m/s2 Po=4nx1'0-7 T'mlA c:3x108 m/s h:6.626x10-34 J-s :4.136x10-15 eV-s me : 9.11x10-31 kg leV: 1.602x10-1e J 1 GY: I J/kg I rad: 0.01 Gy (this Workout Exam has an extra problem for good measure) Page I A) B)c) D) E) A point source emits electromagnetic energy at a rate of 100 W. The intensity l0 m from the source is: l0 Wm2 1.6Wlmz I Wm2 0.024W/m2 0.080 Wm2 A positively charged particle is moving through uniform fields E and B, which are directed in the positive.r and positivey directions, respectively. If there is no resultant force on the particle, then its velocity is in the negative z direction. positive z direction. positive.r direction. negative x direction. positive y direction. A) B)c) D) E) Page2 3. An electron and a proton each travel with equal speeds around circular orbits in the same uniform magnetic field, as shown in the diagram (not to scale). The field is into the page on the diagram. Because the electron is less massive than the proton and because the electron is negatively charged and the proton is positively charged: the electron travels counterclockwise around the smaller circle and the proton travels clockwise around the larger circle the electron travels counterclockwise around the larger circle and the proton travels clockwise around the smaller circle the electron travels clockwise around the smaller circle and the proton travels counterclockwise around the larger circle. the electron travels counterclockwise around the smaller circle and the proton travels counterclockwise around the larger circle the electron travels clockwise around the larger circle and the proton travels counterclockwise around the smaller circle A 100-turn coil has a radius of 7.50 cm and a resistance of 50.0 Q. At what rate must a perpendicular magnetic field change to produce a current of 5.00 A in the coil? 134 T/s 106 T/s 275 Tls 329 Tls 141 T/s 5. An astronomer observes electromagnetic waves emitted by oxygen atoms in a distant galaxy that have a frequency of 5.710 x 1Ora Hz. lnthe laboratory on earth, oxygen atoms emit waves that have a frequency of 5.841 x 1Ora Hz. Determine the relative velocity of the galaxy with respect to the astronomer in earth. L) 6.724 x 106 m/s, toward earth B) 4.369 x 104 m/s, toward earth C') 4.369 x 104 m/s, away from earth D) 2.931 x 108 m/s, away from earth F,) 6.724 x 106 m/s, away from earth A) B) c) D) E) 4. A) B)c) D) E) Page 3 6. A) B)c) D) E) Two identical bar magnets are dropped from equal heights. Magnet A is dropped over bare earth and magnet B over a metal plate. Which magnet strikes first? whichever has its N pole toward the ground magnet A magnet B whichever has its S pole toward the ground both strike at the same time 7. A circular loop of wire 1.0 cm in radius carries a current of 30 A. The magnetic field at the center of the loop is A) 12 pT B) 3.8 mT C) 48 pT D) 2.4 mT E) 1.9 mT 8. X XXX uX 8in R=3.5kQ X XXXXXXX A wire rod rolls with a speed of 8.0 m/s on two metallic rails, 30 cm apart, that form a closed loop. A uniform magnetic field of magnitude l.z0T is into the page. The magnitude and direction of the current induced in the resistor R are A) 1.2 A, clockwise. B) 0.82 A, clockwise. C) 1.2 A, counterclockwise. D\ 2.9 A, counterclockwise. E) 0.82 A, counterclockwise. XXX X Page 4 9. A rectangular loop has sides of length 0.06 m and 0.08 m. The wire carries a current of 10 A in the direction shown. The loop is in a uniform magnetic field of magnitude 0.2 T and directed in the positive x direction. What is the magnitude of the torque on the loop? A) g.l x l0-3 N.m B) q.O x 10-3N.m C\ q.z x 10-2N.m D) +.9 x 10-2N.m E) +.S x l0-3 N.m 10. A 200-tum coil rotates in a magnetic field of magnitud e 0.25 T at a frequency of 60 Hz. The area of the coil is 5.0 cm'. what is the maximum emf in the coil? A) 24VB) e.0 v c) r.5 v D) 4.5 V E) e.4 V 11. An electron is moving with a speed of 3.5 x 105 m/s when it encounters a magnetic field of 0.60 T. The direction of the magnetic field makes an angle of 60.0o with respect to the velocity of the electron. What is the magnitude of the magnetic force on the electron? A) g.+ x l0-raN B) t.zx lo-r3N C) 4.9 x l0-r3N D) 2.9 x lO-raN E\ z.z x lo-13 N Page 5 12. A) B)c) D) E) Use the following to answer question l2: A power plant produces a voltage of 6.0 kv and 150 A. The voltage is stepped up to 240 kV by a transformer before it is transmitted to a substation. The resist.ance of the transmission line between the power plant and the substation is 75 o. what is the current in the transmission line from the plant to the substation? 7.0 A 6.4 A 7.5 A 5.2 A 3.8 A 13. A concave miror in an amusement park has a radius of curvature of 4.0 m. A child stands in front of the mirror so that she appears 2.5 times taller than her actual heieht. If the image is upright, how far is she standing from the mirror? A) 3.5 m B) 7.0 m C) 4.0 m D) 1.2 m E) 2.8 m 14. Two long straight wires are parallel and carry current in opposite directions. The currents are 8.0 A and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is: 0 4.0 x lOa 8.0 x l0+ 12 x l}a 20 x l}a Two long, straight parallel wires 9.3 cm apaft carry currents of equal magnitude L They repel each other with a force per unit length of 5.g nN/m. The curent r is approximately 2.7 mA 43 mA 27 mA 65 mA 52 mA A) B)c) D) E) 15. A) B)c) D) E) Page 6 16. A) B)c) D) E) A 20-pF capacitor is charged to 200 V and is then connected across a 1000-Q resistor. The amount of charge on the capacitor after 10 ms is approximately 1.6 mC 14 mC 2.4 mC 3.2 mC 0.80 mC 17. The peak value of the electric field component of an electromagnetic wave is E. At a particular instant, the intensity of the wave is of 0.020 Wm2. If electric field were increased to 5E, what would be the intensity of the wave? A) 1.0 Wm'^ B) 0.25 Wm' C) 0.50 Wm'^ D) 0.020 Wm' E) 0.10 Wm' The figure shows variation of the cunent through the heating element with time in an iron when it is plugged into a standard 120 V(rms), 60Hz outlet. +10 j(A) 0 -10 What is the approximate average power dissipated in the iron? 1200 w 1700 w 600 w 850 W 450 W 18. A) B)c) D) E) PageT I 19.Four perfectly polarizing plates are stacked so that the axis of each plate is turned 30o clockwise with respect to that of the plate above it. The percentage of the incident unpolarized light that is transmitted by the stack is approximately 27% 21% zero 6.3% 0.78% Two coils share a common axis as shown in the figure. The mutual inductance of this pair of coils is 6.0 mH. If the cunent in coil I is changing at the rate of 3.5 A/s, what is the magnitude of the emf generated in coil2? rarlftfffffn ffffftj t llllll | | t I I r r | |t$ttttu \.\ttLV coil I coil2 1.5 x 10-2V 2.1 x 10-2V 1.7 x 10-3 V 3.5 x l0-3 V 5.8 x 104 V 21. A convex mirror has a radius of curvature of 0.50 m. Where must an object be placed in front of the miruor such that the image is formed 0.15 m behind the mirror? A) 0.19 m B) 0.57 m C) 0.093 m D) 0.38 m E) 0.77 m A) B)c) D) E) 20. A) B)c) D) E) Page 8 --.t Answer Key 1.E 2.8 3.C 4.8 5.8 6.8 7.4 8.8 9.A 10. E 11. D 12. E 13. D 14. E 15. E 16. C 17. c 18. D 19. B 20. B 21. D Page9

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