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Physics 202 Midterm Exam 2 Practice Exam Name: ___________________________________ Student ID: ______________ Section: ___________________________________ TA (please circle): Daniel Crow Aaron Levine Scott Douglas Andrew Loveridge Yutao Gong Jason Milhone Taylor Klaus Hojin Yoo Instructions: 1. Don't forget to write down your name, student ID#, and section number. You need to do this on (this page of your test book and on your Scantron sheet as well, where you should fill in your student ID number under Identification number and your three digit section number starting with 3 under special codes). 2. Answer all multiple questions in this test book by indicating the best answer among choices. You must do this both on your test book and on your Scantron sheet. Follow instructions on the Scantron sheet on how to mark valid answers. 3. When you finish, you need to turn in both this test book and the Scantron sheet. 4. Use the blank side of question pages as additional draft spaces. An extra blank sheet is provided at the end of the test book. 5. Only one answer is allowed per problem/question/ All problems have equal weight. Constants: Permeativity of free space (mu_0) = 4 Pi x10- 7 N/A2 , g=9.81m/s2 1. A 10-gauge copper wire (diameter = 2.588 mm, ρ = 1.7 × 10– 8 Ω of 0.32 Ω. How long is the wire? A) 4.0 × 102 m B) 1.6 km C) 99 m D) 31 m E) 65 m Page 1 m) has a total resistance 2. A comparison of the power losses (P1 , P2 , or P3 ) in the resistors of the circuit in the diagram shows that, if R1 = R2 = R3 , A) B) C) D) E) 4P1 = P2 = P3 P1 = 2P2 + 2P3 P1 = P2 = P3 P1 = (1/2)P2 = (1/2)P3 P1 = P2 + P3 3. In this circuit, the current I through the battery is approximately A) B) C) D) E) 1.7 A 4.4 A 0.36 A 0.60 A 3.4 A Page 2 4. You connect resistors of 2 Ω, 3 Ω, and 6 Ω in parallel across a battery. The current through the 6-Ω resistor is 3 A. What are the currents in the other two resistors? A) B) C) D) E) I1 = 9 A; I2 = 6 A I1 = 6 A; I2 = 9 A I1 = 1 A; I2 = 1.5 A The answer cannot be obtained without knowing the emf of the battery. None of these is correct. 5. A 20.0-µF capacitor is charged to 200 V and is then connected across a 1000-Ω resistor. What is the initial current just after the capacitor is connected to the resistor? A) 100 mA B) 200 mA C) 150 mA D) 300 mA E) 50 mA 6. A straight wire segment 3.0 m long makes an angle of 28° with a uniform magnetic field of 1.0 T. The magnitude of the force on the wire if it carries a current of 1.5 A is approximately A) 2.1 N B) 4.0 N C) 1.4 N D) 0.70 N E) 4.7 N Page 3 7. In a mass spectrometer ions of Ni with mass 9.62 × 10–26 kg and charge +2e are accelerated through a potential difference of X volts and then deflected in a magnetic field of 0.15 T. If the radius of curvature of the ions is 0.55 m, then calculate the value of the potential difference X. A) 5.7 kV B) 274 kV C) 137 kV D) 11.3 kV E) none of the above 8. A beam of charged particles moving with a speed of 106 m/s enters a uniform magnetic field of 0.1 T at right angles to the direction of motion. If the particles move in a radius of 0.2 m, then calculate their period of motion. A) 6.3 × 10– 7 s B) 1.3 × 10– 7 s C) 1.3 × 10– 6 s D) 4.1 × 10– 7 s E) none of the above 9. A circular 10-turn coil with a radius of 5.0 cm carries a current of 5 A. It lies in the xy plane in a uniform magnetic field = 0.05 T + 0.12 T . The coil rotates so that its magnetic moment, µ, is aligned with the magnetic field. The potential energy of the system when the coil's magnetic moment is aligned with the field is A) B) C) D) E) 86.3 mJ 51.1 mJ 28.2 mJ –28.2 mJ –51.1 mJ Page 4 10. A current I passes through a slab of metal in the presence of a magnetic field B. Between which two sides does a Hall voltage develops? Write the side with the higher potential first. The labels are: a and b the two sides on the left and right, c and d the two sides on the front and back, and e and f the top and bottom respectively. A) B) C) D) E) a and b c and d e and f b and a d and c 11. A particle with charge q = 5 µC is moving with velocity = 0, it is located at the origin. The magnetic field at A) B) C) D) E) None of these is correct. Page 5 . At t at t = 0 is 12. An electron beam travels counterclockwise in a circle of radius R in the magnetic field produced by the Helmholtz coils as shown. If you increase the current in the Helmholtz coils, the electron beam will A) B) C) D) E) increase its radius. decrease its radius. maintain the same radius. reverse and travel clockwise with the same radius. reverse and travel clockwise with a larger radius. 13. Two straight rods 60 cm long and 2.0 mm apart in a current balance carry currents of 18 A each in opposite directions. What mass must be placed on the upper rod to balance the magnetic force of repulsion? A) 0.50 g B) 0.99 g C) 9.7 g D) 4.3 g E) 1.6 g Page 6 Use the following to answer question 14. 14. The tightly wound toroid shown consists of 100 turns of wire, each carrying a current I = 3 A. If a = 12 cm and b = 15 cm, the magnetic field at r = 10 cm, due to the current in this toroid, is (µ0 = 4π × 10– 7 N/A2 ) A) 400 µT B) 500 µT C) 600 µT D) zero E) impossible to calculate without additional information. 15. A long straight wire of radius R carries a current density J = kr A/m2 where k is a constant. The magnetic field for r > R is (Hint: Current enclosed .) A) µ0 kR3 /3r B) 2πµ0 kR3 /3r C) 2πµ0 kR2 /r D) 2πµ0 kR/2 E) none of the above Page 7 16. A rectangular loop of wire (0.10 m by 0.20 m) carries a current of 5.0 A in a counterclockwise direction. The loop is oriented, as shown, in a uniform magnetic field of 1.5 T. The magnetic flux of is A) B) C) D) E) 0.026 T m2 1.3 T m2 0.015 T m2 0.030 T m2 1.5 T m2 17. A square coil of wire with side 8.0 cm and 50 turns sits in a uniform magnetic field that is perpendicular to the plane of the coil. The coil is pulled quickly out of the magnetic field in 0.2 s. If the resistance of the coil is 15 ohm and a current of 12 mA is induced in the coil, calculate the value of the magnetic field. A) 5.6 T B) 0.11 T C) 7.5 × 10– 3 T D) 1.4 T E) 9.1 T Page 8 18. A bar magnet is dropped through a loop of copper wire as shown. Recall that magnetic field lines point away from a north pole and toward a south pole. If the positive direction of the induced current I in the loop is as shown by the arrows on the loop, the variation of I with time as the bar magnet falls through the loop is illustrated qualitatively by which of the following graphs? The time when the midpoint of the magnet passes through the loop is indicated by C. A) B) C) D) E) 1 2 3 4 5 Page 9 Use the following to answer question 19. 19. A rectangular coil of length l = 20 cm and width w = 15 cm is moving at a constant speed v = 5 m/s. It enters a region of uniform magnetic field B = 0.2 T from the left. While the coil is completely immersed in the field, the voltage across points a and b is A) 0.20 V B) 0.15 V C) –0.20 V D) –0.15 V E) zero Page 10 Use the following to answer question 20. 20. A classic demonstration illustrating eddy currents is performed by dropping a permanent magnet inside a conducting cylinder. The magnet does not go into free fall. Instead it reaches terminal velocity and can take a few seconds to drop a length of about a meter. Suppose the mass of the magnet is 70 g and width of 1.0 cm. It falls with a terminal velocity of 10 cm/s and the length of the pipe is 80 cm. The magnitude of the Joule heating from the eddy currents is approximately A) 0.55 J B) 8.8 × 10-5 J C) 1.1 J D) 1.8 × 10-4 J E) None of these is correct. Page 11 Answer Key - Midterm2_practice 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. C B A A B A D C E B A B B D A A B A E A Page 12