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Name: ________________________ Class: ___________________ Date: __________ ID: A Chapter 22 Multi-format Test Modified True/False Indicate whether the statement is true or false. If false, change the identified word or phrase to make the statement true. ____ 1. The unit used to measure the strength of a magnetic field is the ohm. _________________________ ____ 2. As the distance between two magnets increases, the force between their magnetic fields decreases. _________________________ ____ 3. Earth’s core acts as a permanent magnetic in producing Earth’s magnetic field. _________________________ ____ 4. A generator changes electrical energy to mechanical energy. __________________________ ____ 5. The rotating element of a motor is referred to as the field coil. _________________________ Completion Complete each statement. Select the correct term to complete each sentence. There are extra terms in the list. north attract permanent generator magnet repel electromagnet electric motor south field induction alternating 6. The influence created by a magnet that exerts forces on other magnets is called a magnetic ____________________. 7. If two opposite poles of magnets are facing each other, the magnets will ____________________ one another. 8. Earth’s core is surrounded by a magnetic field aligned so that its magnetic south pole is located near its geographic ____________________ pole. 9. In ____________________ magnets, the magnetic fields of individual atoms are aligned in a similar direction. 10. Electromagnetic ______________________________ occurs when current is induced in a wire by a moving magnet. 11. A device that changes mechanical energy to electrical energy is a ____________________. 12. The current produced by a generator is always ____________________ current. Short Answer 13. Is it possible to have a magnet with only a north pole? Explain. 14. What two pieces of information can you get from a magnetic field diagram? 1 Name: ________________________ ID: A 15. The forces between two magnets depend upon the magnets’ alignment. Explain how to cause attractive and repulsive forces between two magnets. 16. Several compasses are placed around a bar magnet. Which end of the magnet is its north pole? 17. In this diagram of Earth’s magnetic field, where is the magnetic field the strongest? 18. A strong magnet and a weak magnet are placed north pole to south pole and are attracted to each other with a magnetic force. Which magnet has the stronger force? 19. Describe how to make an electromagnet. 20. Name two ways to increase the strength of an electromagnet. 21. What happens when you place a compass near a current-carrying wire? 22. Name 3 devices that use electromagnets in their operation. 23. Strong electromagnets are used in junk yards for moving large pieces of iron from place to place. What is the advantage in using an electromagnet instead of a large permanent magnet? 24. What is the purpose of a commutator in an electric motor? 25. A bar magnet is suspended so that it is free to rotate. When you hold a second bar magnet near the suspended magnet, the suspended magnet begins to rotate. Explain what must be done to keep the magnet rotating. 2 Name: ________________________ ID: A 26. How can you induce current in a wire using a permanent magnet? Problem 27. In which direction will the rotating disk spin? Essay 28. Explain how an electric motor works. Be sure to use the words rotor, commutator, permanent magnets, and electromagnets. Other The diagram represents an iron nail wrapped with a current carrying wire. Figure 22-1 29. What type of device does Figure 22-1 represent? 30. Label the pointed end and the head of the nail in Figure 22-1 with an “N” and “S” to represent the magnetic north and south poles of the nail. 3 ID: A Chapter 22 Multi-format Test Answer Section MODIFIED TRUE/FALSE 1. ANS: F, gauss DIF: basic REF: section 22.1 2. ANS: T 3. ANS: F, electromagnet DIF: basic DIF: basic REF: section 22.1 4. ANS: F, electric motor DIF: basic 5. ANS: F, armature DIF: basic REF: section 22.3 REF: section 22.3 COMPLETION 6. ANS: field DIF: basic 7. ANS: attract REF: section 22.1 DIF: basic 8. ANS: north REF: section 22.1 DIF: intermediate 9. ANS: permanent REF: section 22.1 DIF: basic 10. ANS: induction REF: section 22.2 DIF: basic 11. ANS: generator REF: section 22.3 DIF: basic 12. ANS: alternating AC REF: section 22.3 DIF: intermediate REF: section 22.3 1 REF: section 22.1 ID: A SHORT ANSWER 13. ANS: No. All magnets have two opposite poles, north and south. It is impossible to have only a north or south pole by itself. DIF: basic REF: section 22.1 14. ANS: The direction and the relative strength of the magnetic field DIF: intermediate REF: section 22.1 15. ANS: Attractive forces exist between two magnets when unlike poles face each other. Repulsive forces exist when like poles are facing on another. DIF: intermediate 16. ANS: B REF: section 22.1 DIF: intermediate REF: section 22.1 17. ANS: At point B. The field is strongest at the north or south magnetic poles, not at the north or south geographic poles. DIF: advanced REF: section 22.1 18. ANS: According to Newton’s third law, they exert the same force on each other. DIF: advanced REF: section 22.1 19. ANS: Electromagnets are magnets created when there is electric current flowing in a wire. The simplest electromagnet uses a coil of wire that must be wrapped around a piece of metal. Iron is often used. Because iron is magnetic, it concentrates the magnetic field created by the current in the coil. DIF: basic REF: section 22.2 20. ANS: Any two of these three answers is correct: Increase current flow in the wire, increase amount of iron/steel in the core, increase the number of turns of wire in the coil. DIF: basic REF: section 22.2 21. ANS: The compass needle moves as if the wire were a magnet. DIF: intermediate REF: section 22.2 2 ID: A 22. ANS: Answers may vary. Correct answers include: Doorbells, speakers, microphones, motors, toasters, maglev trains DIF: intermediate REF: section 22.2 23. ANS: Once the permanent magnet is attracted to the heavy metal piece, it would be difficult to free the metal from the magnet. The electromagnet will lose its magnetism when the current is turned off. DIF: advanced REF: section 22.2 24. ANS: The commutator switches the polarity of the electromagnet from north to south and back again. Switching the polarity makes the rotor turn. DIF: basic REF: section 22.3 25. ANS: To keep the magnet spinning, you need to reverse the hand-held magnet as each end of the suspended magnet comes by. DIF: intermediate REF: section 22.3 26. ANS: You can induce current either by moving the permanent magnet through a coil of wire or by moving a coil of wire over the permanent magnet. DIF: intermediate REF: section 22.3 PROBLEM 27. ANS: Counterclockwise DIF: intermediate REF: section 22.3 ESSAY 28. ANS: A motor has a spinning disk called a rotor. When the rotor is spinning, the motor can do useful work. The rotor has magnets along its outside edge. In some motors, these are permanent magnets. Other motors use electromagnets. Outside the rotor there is another magnet (or set of magnets). A commutator causes the magnet to reverse its polarity from north to south and back again. As the polarity changes, the magnets in the rotor are first attracted and then repelled by the “outer” magnet. This action is similar to the pull-and-then-push action that we use to turn a merry-go-round. The attracting and repelling action of the “outer” magnet causes the rotor to turn.. DIF: intermediate REF: section 22.3 3 ID: A OTHER 29. ANS: It represents an electromagnet. DIF: basic REF: section 22.2 30. ANS: N at the “head” and S at the “point” DIF: advanced REF: section 22.2 4 Chapter 22 Multi-format Test [Answer Strip] F _____ 1. T _____ 2. F _____ 3. F _____ 4. F _____ 5. ID: A