Magnetism Review Questions with Answers

Magnetism Review 1. An electric current flows through a solenoid as shown below. What is the direction of the magnetic field inside the solenoid? 2. A long conductor is placed in a 0.65T magnetic field as shown below. What are the magnitude and direction of the current that produces a 1.6N force on the wire directed up the page? 3. A proton has a speed of 5.0x106m/s while travelling perpendicular to a 0.14T magnetic field. What is the magnetic force on the proton? 4. The flux through a circular coil with a radius of 0.075m is 0.013Wb when placed perpendicular to a magnetic field. What is the strength of the magnetic field? 5. The diagram below shows an aluminum ring and the current induced in it by the nearby magnet that is free to move along its central axis. The magnet must be A. stationary. B. moving to the left. C. moving to the right. D. spinning about its central axis. 6. A loop of wire of area 0.32m2 is placed in a 0.75T magnetic field as shown. The magnetic field is changed to 0.35T in the opposite direction in 0.45s. What are the magnitude and direction of the current length through the 15Ω resistor? 7. Which of the following diagrams best shows the magnetic field lines between the poles of two permanent magnets? 8. A wire carrying 12A of current is placed in a magnetic field of strength 0.63T. What are the magnitude and direction of the magnetic force acting on the wire? 9. A 460-turn solenoid having a diameter of 0.024m is 0.14m long. What is the magnetic field at the center of the solenoid when a 13A current flows through it? A. 0T B. 5.4x10-2T C. 3.1x10-1T D. 6.3x10-1T 10. A conducting rod is moving perpendicular to a uniform magnetic field of 0.23T at a velocity of 9.2m/s. What emf is generated during this motion? 11. A rectangular coil measuring 0.12m by 0.080m is placed is placed perpendicular to a 0.85T magnetic field as shown. What is the magnetic flux through the coil? 12. A single loop of wire of radius 0.23m is placed in a 0.75T magnetic field as shown. The magnetic field is changed to a strength of 0.50T in the opposite direction in 0.61s. What is the average emf induced in the coil? 13. With the electromagnet turned off, electrons in a cathode ray tube strike the center of the screen as shown. When the electromagnet is turned on, where will the electron beam now strike the screen? A. 1 B. 2 C. 3 D. 4 14. Which of the following diagrams best shows the magnetic field due to a long straight wire carrying a conventional current I as shown? 15. A proton is travelling at 2.3x106m/s in a circular path in a 0.75T magnetic field. What is the magnitude of the force on the proton? 16. A solenoid of length 0.75m has a radius 0.092m. A current of 25A flows through its 4700 turns. Within this solenoid a 0.10m long conductor moves at 4.3m/s perpendicular to the field in the solenoid. What emf is induced between the ends of the conductor? 17. A rectangular coil of wire containing 250 loops is placed in a magnetic field. Each loop measures 0.075m by 0.28m. The magnetic field changes over a time interval of 0.36s producing an average emf of 1.3V. What is the change in the magnetic field strength? 18. Which diagram shows the magnetic field created near a conductor carrying current towards the right? 19. In which of the following situations would the greatest emf be induced in the coil? All changes occur in the same time interval. 20. The direction of a magnetic field is determined to be the direction in which A. a positive charge would tend to move. B. a negative charge would tend to move. C. the north end of a compass needle would point. D. the south end of a compass needle would point. 21. A solenoid has a length of 0.30m, a diameter of 0.040m and 500 windings. The magnetic field at its center is 0.045T. What is the current in the windings? 22. An aircraft with a wingspan of 24m flies at 85m/s perpendicular to a magnetic field. An emf of 0.19V is induced across the wings of the aircraft. What is the magnitude of the magnetic field? 23. A beam of positively and negatively charged particles enters a magnetic field as shown. Which paths illustrate the positive and negative charges leaving the magnetic field region? 24. The diagram shows a bar magnet falling through an aluminum pipe. Electric currents are induced in the pipe immediately above and below the falling magnet. In which direction do these currents flow? 25. The diagram shows a conductor between a pair of magnets. The current in the conductor flows out of the page. In what direction will the magnetic force act on the conductor? 26. What are the units of magnetic flux? A. B. C. D. T Wb T •m/A D • m/C2 27. The diagram shows a coil with 25 windings and dimensions 0.15m by 0.20m. Its plane is perpendicular to a magnetic field of magnitude 0.60 T. If the coil rotates 90° in 4.17 x 10-2 s so that its plane is now parallel to the magnetic field, what average emf is induced during this time? 28. The diagram shows a magnet suspended near a solenoid. After the solenoid has been connected to a power supply, the magnet rotates to a new position with its South Pole pointing towards the solenoid. What arrows show the direction of the current in the solenoid and the direction of the magnetic field caused by this current? 29. A charged particle travels in a circular path in a magnetic field. What changes to the magnetic field and to the velocity of the particle would both cause the radius of its path to decrease? 30. The diagram below shows two coils in a magnetic field. An electric current can be induced in the coil oriented with its plane. A. B. C. D. Parallel to a constant magnetic field Parallel to a changing magnetic field Perpendicular to a constant magnetic field Perpendicular to a changing magnetic field 31. The diagram shows a 0.010 kg metal rod resting on two long horizontal frictionless rails which remain 0.40m apart. The circuit has a resistance of 3.0Ω and is located in a uniform 0.20 T magnetic field. Find the initial acceleration and maximum velocity for the rod. 32. A proton with kinetic energy of 2.1 x 10-17 J is moving into a region of charged parallel plates. The proton will be stopped momentarily in what region? 33. Identify the magnetic poles labelled L and R in the diagram shown. 34. The diagram shows current I flowing in a circular coil located in a magnetic field. The magnetic force acting on the coil will tend to cause it to A. B. C. D. Expand Contract Move up the page Move down the page 35. An aircraft whose wingspan is 15m carries a static charge of 0.60 C. It travels at 240 m/s perpendicular to a 1.4 x 10-4 T magnetic field. What magnetic force does the aircraft experience? 36. An undeflected electron beam strikes the centre of a cathode ray tube. A solenoid placed besides a cathode ray tube causes the electron beam to strike the screen at position X. What changes to the magnitude and direction of the current in the solenoid would cause the electron beam to strike the screen at Y? 37. A coil having 150 turns and a cross-sectional area of 0.042 m2 is oriented with its plane perpendicular to a 0.12 T magnetic field. If the field increases to 0.66 T in 0.25s, what emf is induced in the coil? 38. The magnetic field at the centre of a solenoid of length 0.25m is 1.2 x 10-2 T. The current in the windings is 7.5 A. A. How many windings does the solenoid have? B. If the cross-sectional area of the solenoid is 8.5 x 10-4 m2, what is the flux through it? 39. In an experiment, a positively charged oil droplet weighing 6.5 x 10-15 N is held stationary by a vertical electric field as show in the diagram. If the electric field strength is 5.3 x 103 N/C, what is the charge on the oil droplet? 40. Which of the following diagrams best represents the magnetic field in the region between the two permanent magnets? 41. In which diagram would the current-carrying conductor experience a magnetic force out of the page? 42. A coil of 25 turns of wire is suspended by a thread. When a current flows through the coil, the tension in the thread is reduced by 4.0 x 10-2 N. What are the magnitude and direction of the current? 43. A bar magnet is moving toward a solenoid. What is the direction of the current through the galvanometer and what is the direction of the magnetic field produced by this current at location P inside the solenoid? 44. The 5.2m long metal rotor blades of a helicopter spin at 6.0 revolutions per second perpendicular to the earth’s magnetic field of 4.7x10-5T. What is the magnetic flux swept out by the rotor blades in one revolution and what is the emf induced between the axis and tip of a rotor blade? 45. a) A proton moves with a speed of 3.6x105m/s at right angles to a uniform 5.0x10-5T magnetic field. What is the radius of curvature for the motion of the proton? b) Describe the path of the proton in the magnetic field and use principles of physics to explain the proton’s motion. Magnetism Review Answers 1. A (Aug. ’99, 24) 2. 11A, right (Aug. ’99, 25) 3. 1.1x10-13N (Aug. ’99, 26) 4. 0.74T (Aug. ’99, 27) 5. C (Aug. ’99, 28) 6. D (Aug. ’99, 30) 7. C (Jan. ’99, 23) 8. 1.1N, down the page (Jan. ’99, 24) 9. 5.4x10-2N (Jan. ’99, 26) 10. 0.32V (Jan. ’99, 27) 11. 8.2x10-3Wb (Jan. ’99, 28) 12. 0.34V (Jan. ’99, 29) 13. D (Jan. ’99, 30) 14. A (June ’99, 25) 15. 2.8x10-13N (June ’99, 26) 16. 0.085V (June ’99, 27) 17. 0.089T (June ’99, 7LA) 18. D (Jan. ’00, 25) 19. D (June ’99, 28) 20. C (Jan. ’00, 25) 21. 21A (Jan. ’00, 27) 22. 9.3x10-5T (Jan. ’00, 28) 23. B (Jan. ’00, 26) 24. B (Jan. ’00, 30) 25. to the left (June ’00, 26) 26. B (June ’00, 24) 27. 11V (Jan. ’00, 7LA) 28. C (June ’00, 25) 29. B (June ’00, 27) 30. D (June ’00, 28) 31. a i = 40m/s2, v max = 1.9x102m/s (June ’00, 30) 32. L (Aug. ’00, 20) 33. L = South, R = North (Aug. ’00, 24) 34. B (Aug. ’00, 25) 35. 0.022N (Aug. ’00, 26) 36. B (Aug. ’00, 27) 37. 9.8V (Aug. ’00, 28) 38. a) 3.2x102 (Aug. ’00, 7LA) b) 1.0x10-5Wb 39. 1.2x10-18C (Jan. ’01, 22) 40. B (Jan. ’01, 25) 41. D (Jan. ’01, 26) 42. 0.16A counter clockwise (Jan. ’01, 27) 43. A (Jan. ’01, 28) 44. A (Jan. ’01, 30) 45. a) 75m b) The path is circular. Moving charge in magnetic field produces a magnetic force. Force is perpendicular to velocity. This perpendicular force (acting on proton) produces circular motion.