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Physics 112 Exam 2 Summer 2014 Name_________________ Physics 112 Summer 2014 Exam 2 Monday, July 14 Directions: This 60-minute exam consists of twenty multiple-choice questions. This test is worth 20% of your final grade. (One point is equal to 1% of the final grade.) The questions on this test are not in order of difficulty. You must mark all of your answers on both your test and answer sheet. In marking the multiple choice bubble sheet use a number 2 pencil. Do not use ink. If you did not bring a pencil, ask for one. Fill in the appropriate circles completely. If you need to change any entry, you must completely erase your previous entry. Carefully read each question and its five possible answers. Select one and only one answer for each question. Choose the answer that is closest to the correct one. When you are finished with the exam, return the bubble sheet, the exam itself, and scratch paper that you used for the exam. Good luck! Page 1 of 7 Physics 112 Exam 2 Summer 2014 21. Positive charge q is moving with velocity v in the magnetic field B as shown below (with vectors v and B on the surface of the page). What is the direction of the magnetic force? v q A) B) C) D) E) Parallel to v Parallel to B Exactly between v and B Into the page Out of the page B 22. A positively charged particle is moving in a magnetic field. What is the angle between the velocity of the charge and the direction of the magnetic field if the magnetic force on the particle is zero? A) B) C) D) E) 90° 45° 30° 0 Magnetic force cannot be zero if the speed of the particle and the magnetic field are not zero. 23. Alpha particles of charge q 2e and mass m 6.6 10 27 kg are emitted from a radioactive source at a speed of 1.6 107 m s . What magnetic field strength would be required to bend them into a circular path of radius r 0.25 m? A) B) C) D) E) 5.3 T 4.3 T 3.3T 2.3 T 1.3 T 24. If a bar magnet is divided into two equal pieces, A) the north and south poles are separated B) two magnets result C) the magnetic properties are destroyed D) an electric field is created E) none of the above Page 2 of 7 Physics 112 Exam 2 Summer 2014 25. An airplane with a wing span of 60 m flies horizontally at a location where the downward component of the Earth's magnetic field is 6.0 × 10-5 T. Find the magnitude of the induced emf between the tips of the wings when the speed of the plane is 225 m/s. A) B) C) D) E) 0.41 V 0.61 V 0.81 V 1.2 V 1.4 V 26. A wire carries a current of 10 A in a direction of 30° with respect to the direction of a 0.30-T magnetic field. Find the magnitude of the magnetic force on a 0.50-m length of the wire. A) 0.75 N B) 1.5 N C) 3.0 N D) 6.0 N E) zero 27. A circular loop of wire of radius 0.50 m is in a uniform magnetic field of 0.30 T. The current in the loop is 2.0 A. What is the magnetic torque when the plane of the loop is perpendicular to the magnetic field? A) B) C) D) E) 0.73 m∙N 0.52 m∙N 0.47 m∙N 0.41 m∙N zero 28. What is the strength of a magnetic field 5.0 cm from a long straight wire carrying 4.0 A of current? A) B) C) D) E) 3.8∙10-6 T 4.9∙10-6 T 1.6 ∙10-5 T 4.7∙10-5 T 5.1∙10-5 T Page 3 of 7 Physics 112 Exam 2 Summer 2014 29. Two long parallel wires carry currents of 5.0 A and 8.0 A in the opposite direction. The wires are separated by 0.30 m. Find the magnetic force per unit length between the two wires. A) B) C) D) E) 2.7∙10-5 N repulsive 7.2∙10-5 N repulsive 2.7∙10-5 N attractive 7.2∙10-5 N attractive zero 30. A long solenoid has 100 turns/cm and carries a current of 1.00A. A sphere of radius 1.00 cm is placed inside the solenoid. Find the magnetic flux through the sphere. A) B) C) D) E) 1.6∙10-6 T∙m2 1.6∙10-7 T∙m2 4.0∙10-8 T∙m2 8.0∙10-8 T∙m2 zero 31. What is the direction of the induced current in the circular loop due to the increasing current shown below? I increasing A) B) C) D) E) Counterclockwise Clockwise The direction of the current is periodically changing Induced current is equal to zero There is not enough information to answer the quastion 32. An AC generator consists of 100 turns (loops) of wire with total resistance 12 Ω. The area of each loop is 0.090 m2. The loops rotate in a magnetic field of 0.50 T at a constant angular speed of 60 revolutions per second. Find the maximum induced emf. A) B) C) D) E) 0.27 kV 0.54 kV 1.7 kV 3.4 kV 5.1 kV Page 4 of 7 Physics 112 Exam 2 Summer 2014 33. Doubling the number of loops of wire in a coil produces what kind of change on the induced emf, assuming all other factors remain constant? A) B) C) D) E) The induced emf increases 4 times The induced emf increases 2 times The induced emf decreases 2 times The induced emf decreases 4 times The induced emf remains the same 34. A simple RL circuit contains a 6.0-Ω resistor and an 18-H inductor. What is this circuit's time constant? A) B) C) D) E) 108 s 3.0 s 0.33 s 0.20 s 0.11 s 35. A 6 V battery is connected to coil 1 of the transformer shown in the figure below. Coil 2 has twice as many turns as coil 1. What is the voltage drop across coil 2? A) B) C) D) E) 12 V 6V 3V 2V 0 1 2 36. The magnetic field inside an air-filled solenoid 36 cm long and 2.0 cm in diameter is 0.80 T. Approximately how much energy is stored in this field? A) B) C) D) E) 5J 11 J 18 J 21 J 29 J Page 5 of 7 Physics 112 Exam 2 Summer 2014 37. What is the current through a 2.50-mH coil due to a 110-V, 60.0 Hz source? A) B) C) D) E) 0.94 A 2.5 A 104 A 117 A 154 A 38. A circular parallel-plate capacitor with plates 4.0 cm in diameter is accumulating charge at the rate of 3.0 mC/s at some instant in time. What is the magnitude of the induced magnetic field at the distance 1.0 cm measured radially outward from the center of the plates at this instant? A) B) C) D) E) 2.0 T 0.5 T 2.0 10 8 T 1.5 10 8 T 0.5 10 8 T 39. An electromagnetic wave in vacuum is moving in +y direction. At time t=0 and at position (x,y,z)=(0,0,0), the electric field is pointing in the +z direction. In what direction is the magnetic field pointing at that time and position? A) B) C) D) E) +x –x +y –y +z 40. If the magnetic field in a traveling EM wave has a peak magnitude of 17.5 nT, what is the peak magnitude of the electric field? A) B) C) D) E) zero 1.75 V/m 3.50 V/m 5.25 V/m 7.00 V/m Page 6 of 7 Physics 112 Exam 2 Summer 2014 Record Sheet You may fill in this sheet with your choices, detach it and take it with you after the exam for comparison with the posted answers 21 31 22 32 23 33 24 34 25 35 26 36 27 37 28 38 29 39 30 40 Page 7 of 7