Magnetism Study Guide

Transcription

1 Magnetism Study Guide 1. If the current in a wire is directed downward, what is the direction of the magnetic field produced by the current? a. counterclockwise in the horizontal plane b. clockwise in the horizontal plane c. in the same direction as the current d. in the opposite direction to the current 2. A coil of wire that is carrying a current and produces a magnetic field is a. a galvanometer. c. a magnetic domain. b. a solenoid. d. an electric motor. 3. In an electric motor, periodically changing the direction of current in the electromagnet can cause the axle to spin because a. the electromagnet loses its magnetism. b. mechanical energy is converted to electric energy. c. the moving electrons push the electromagnet in the opposite direction. d. the magnetic field reverses direction. 4. A device that changes mechanical energy to electrical energy by rotating a coil of wire through a magnetic field is called a(an) a. transformer. c. electromagnet. b. generator. d. current meter. 5. Where is the magnitude of the magnetic field around a permanent magnet greatest? a. close to the poles b. far from the poles c. The magnitude is equal at all points on the field. d. The magnitude depends on the material of the magnet. 6. A solenoid is in an upright position on a table. A counterclockwise current of electrons causes the solenoid to have a(n) magnetic pole at its bottom end. If a compass is placed at the top of the solenoid, the north pole of the compass would be a. north; attracted c. north; repelled b. south; attracted d. south; repelled 7. In a permanent magnet, a. domain alignment persists after the external magnetic field is removed. b. domain alignment becomes random after the external magnetic field is removed. c. domains are always randomly oriented. d. the magnetic fields of the domains cancel each other. 8. In soft magnetic materials such as iron, what happens when an external magnetic field is removed? a. The domain alignment persists. b. The orientation of domains fluctuates. c. The material becomes a hard magnetic material. d. The orientation of domains changes, and the material returns to an unmagnetized state. 9. According to Lenz s law, if the applied magnetic field changes, a. the induced field attempts to keep the total field strength constant. b. the induced field attempts to increase the total field strength. c. the induced field attempts to decrease the total field strength. d. the induced field attempts to oscillate about an equilibrium value. 10. The direction of the force on a current-carrying wire in an external magnetic field is a. perpendicular to the current only. b. perpendicular to the magnetic field only. c. perpendicular to the current and to the magnetic field. d. parallel to the current and to the magnetic field.

2 11. A positive charge, Q, is located in a magnetic field, B, which is directed toward the right, as shown in the figure above. If Q travels toward the top of the page, the direction of the magnetic force on Q is a. toward the right. c. away from you, into the page. b. toward you, out of the page. d. There is no magnetic force. 12. Which conversion process is the basic function of the electric motor? a. mechanical energy to electrical energy b. electrical energy to mechanical energy c. low voltage to high voltage, or vice versa d. alternating current to direct current 13. There are four coils of wire being used as electromagnets. They all have the same size and are made up of the same material but have a different number of loops. Which coil will produce the weakest magnetic field when the same amount of current passes through all of the coils? a. a coil having 10 loops c. a coil having 30 loops b. a coil having 25 loops d. a coil having 45 loops 14. A/An is a long coil of wire with many loops used to create a large magnetic field. a. solenoid c. electric motor b. electromagnet d. armature 15. A/An is described as the area around a magnet where other magnets would be accelerated. a. magnetic field c. domain b. magnetic flux d. solenoid 16. Which factor will not affect the strength of a solenoid? a. number of wraps c. radius of the wraps b. strength of current d. core type 17. What are the units of electromotive force? a. newtons c. volts b. newtons per coulomb d. volts per ampere 18. The number of turns on the primary coil of a step-down transformer the number of turns on the secondary coil. a. equals c. is less than b. is greater than d. is unrelated to 19. A generator is used to light a bulb. Energy for lighting the bulb actually comes from a. a plug where the generator is connected to the wall. b. a mechanical input to the generator. c. the magnet in the generator. d. the coil of wire. e. none of the above 20. The principal advantage of AC power over DC power is that a. AC voltage oscillates, whereas DC voltage does not. b. lower voltages are used. c. AC circuits multiply power more easily. d. AC voltage can be transformed more easily. e. AC circuits are safer.

3 21. Magnetism is produced by the motion of electrons as they a. move around the nucleus. b. spin on their axes. c. both A and B d. none of the above 22. If you put a small compass in a magnetic field, the compass will a. line up in a direction parallel to the magnetic field lines. b. swing randomly. c. line up in a direction perpendicular to the magnetic field lines. d. seek electrical charge concentrations. 23. Magnetic field strength is a. strongest close to a magnet. b. constant everywhere around a magnet. c. strongest far from a magnet. 24. Magnetic domains are a. regions that may or may not be magnetized. b. clusters of atoms randomly aligned. c. regions of atoms magnetically aligned. d. blocks of material. 25. Earth's magnetic field is most likely due to a. millions of small magnets buried in Earth. b. a magnetized solid inner core of Earth. c. convection currents in the molten part of Earth's interior. d. the rotation of Earth acting on all of Earth's electrons. e. none of the above 26. Fill in the chart. Charge Direction particle is traveling Direction of magnetic field Direction of force - Upward North + North West - Upward East + South Downward - Downward West + Upward East 27. In a particle accelerator a positron (C= +1.6 x ) travels through a perpendicular magnet field with a magnitude of 3.1 x 10-2 T. At what speed must the positron travel in order for it to experience a force of 4.75 x N? 28. An alpha particle (2 protons and 2 neutrons) experiences a downward force of 2.9 x N while traveling in a magnetic field with a strength of 5.1 x T pointing to the north. Find the speed of the particle and the direction it must be traveling in. 29. Find the length of a wire if it experiences a.63n force when it travels through a magnetic field with a strength of 0.85T whilst carrying 5.0 amps of current. 30. A coil with 462 turns of wire, a total resistance of 36Ω, and a cross-sectional area of 0.25 m 2 is positioned with its plane perpendicular to the field of a powerful electromagnet. What average current is induced in the coil during the 0.37s that the magnetic field drops from 3.1 T to 0.0 T? 31. A step-up transformer has a potential difference across the primary of 28 V and a potential difference across the secondary of V. There are 28 turns in the primary coil. How many turns are in the secondary? 32. A step-up transformer is used to create a potential difference of V across the secondary. The potential difference across the primary is 121 V and the secondary has turns. How many turns are in the primary?

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5 Mag Answer Section MULTIPLE CHOICE 1. ANS: B PTS: 1 DIF: L2 OBJ: STA: C.a C 2. ANS: B PTS: 1 DIF: L1 OBJ: ANS: D PTS: 1 DIF: L2 OBJ: STA: C 4. ANS: B PTS: 1 DIF: L1 OBJ: ANS: A PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: I OBJ: ANS: A PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: I OBJ: ANS: C PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: I OBJ: ANS: A PTS: 1 DIF: II OBJ: ANS: B PTS: 1 DIF: I OBJ: ANS: A In a uniformly looped coil, the magnetic field produced by each loop is the same. As all the loops add to the strength of the field of the coil, the higher the number of loops in the coil, the stronger the field. A B C D Feedback The coil with the maximum number of loops will produce the strongest magnetic field. To produce the strongest magnetic field, the coil should have the maximum number of loops. The more loops in a coil, the stronger the magnetic field. Correct! PTS: 1 DIF: Bloom's Level 2 REF: Page 649 OBJ: Compare and contrast various magnetic fields. TOP: Compare and contrast various magnetic fields. KEY: Electromagnet MSC: 3 NOT: /a/ The coil with the maximum number of loops will produce the strongest magnetic field. /b/ To produce the strongest magnetic field, the coil should have the maximum number of loops. /c/ The more loops in a coil, the stronger the magnetic field. /d/ Correct! 14. ANS: A A solenoid is a long coil of wire. PTS: 1 DIF: Bloom's Level 2 REF: p. 649 NAT: E ANS: A Magnetic fields exist around magnets and affect other magnets. PTS: 1 DIF: Bloom's Level 2 REF: p. 646 NAT: B ANS: C

6 The radius of the wraps in a solenoid will not affect the strength of the magnetic field that it produces. PTS: 1 DIF: Bloom's Level 4 REF: p. 649 NAT: B ANS: C Electromotive force is measured in volts. PTS: 1 DIF: Bloom's Level 1 REF: p. 673 NAT: B ANS: B A step-down transformer has more wraps in its primary coil than in its secondary coil. PTS: 1 DIF: Bloom's Level 1 REF: pp NAT: E ANS: B PTS: 1 DIF: L2 OBJ: 37.3 Generators and Alternating Current STA: MO.SC.1.2.A.e MO.SC.2.2.C MO.SC.2.2.C.a MO.SC.8.1 KEY: generator energy 20. ANS: D PTS: 1 DIF: L2 OBJ: 37.6 Power Transmission STA: MO.SC.1.2.A.e MO.SC.7.1.E.a.2 KEY: AC DC transform 21. ANS: C PTS: 1 DIF: L2 OBJ: 36.3 The Nature of a Magnetic Field STA: MO.SC.1.2.A.e MO.SC.2.2.C MO.SC.2.2.C.b KEY: magnetism electron 22. ANS: A PTS: 1 DIF: L2 OBJ: 36.2 Magnetic Fields STA: MO.SC.1.1.G MO.SC.2.2.C MO.SC.2.2.C.b MO.SC.7.1.C.a KEY: compass magnet 23. ANS: A PTS: 1 DIF: L1 OBJ: 36.2 Magnetic Fields STA: MO.SC.1.1.G MO.SC.2.2.C MO.SC.2.2.C.b MO.SC.7.1.C.a KEY: strength field MSC: knowledge 24. ANS: C PTS: 1 DIF: L1 OBJ: 36.4 Magnetic Domains STA: MO.SC.1.1.G MO.SC.2.2.C MO.SC.2.2.C.b MO.SC.7.1.C.a KEY: domain magnet MSC: knowledge 25. ANS: C PTS: 1 DIF: L1 OBJ: 36.9 Earth's Magnetic Field STA: MO.SC.2.2.C MO.SC.2.2.C.b MO.SC.7.1.E.a.2 KEY: Earth magnetic convection MSC: knowledge