Magnetism Preview Understanding Concepts Reading Skills Interpreting Graphics

Understanding Concepts 1. A straight vertical wire is carrying an electric current. Positive charges are flowing straight down. What is the direction of the magnetic field generated by the wire as viewed from above? A. straight up B. straight down C. clockwise D. counterclockwise

Understanding Concepts, continued 1. A straight vertical wire is carrying an electric current. Positive charges are flowing straight down. What is the direction of the magnetic field generated by the wire as viewed from above? A. straight up B. straight down C. clockwise D. counterclockwise

Understanding Concepts, continued 2. What type of device is used to measure the current in an electromagnet? F. an electric motor G. a galvanometer H. a generator I. a solenoid

Understanding Concepts, continued 2. What type of device is used to measure the current in an electromagnet? F. an electric motor G. a galvanometer H. a generator I. a solenoid

Understanding Concepts, continued 3. A charged particle is moving through a magnetic field. In which direction is the particle moving when the magnetic force acting on the particle is at its greatest? A. in the same direction as the magnetic field lines B. in the opposite direction from the magnetic field lines C. at right angles to the magnetic field lines D. clockwise around the magnetic field lines

Understanding Concepts, continued 3. A charged particle is moving through a magnetic field. In which direction is the particle moving when the magnetic force acting on the particle is at its greatest? A. in the same direction as the magnetic field lines B. in the opposite direction from the magnetic field lines C. at right angles to the magnetic field lines D. clockwise around the magnetic field lines

Understanding Concepts, continued 4. In an AC generator, a loop of wire rotates between two magnetic poles. At what angle(s) of rotation relative to the magnet does the loop generate the most current? F. 0˚ and 180˚ G. 90˚ and 270˚ H. 180˚ I. 360˚

Understanding Concepts, continued 4. In an AC generator, a loop of wire rotates between two magnetic poles. At what angle(s) of rotation relative to the magnet does the loop generate the most current? F. 0˚ and 180˚ G. 90˚ and 270˚ H. 180˚ I. 360˚

Understanding Concepts, continued 5. How would a compass located precisely at the Earth’s geographic north pole behave?

Understanding Concepts, continued 5. How would a compass located precisely at the Earth’s geographic north pole behave? Answer: It would point toward the magnetic north pole.

Understanding Concepts, continued 6. What is the difference between a solenoid and an electromagnet?

Understanding Concepts, continued 6. What is the difference between a solenoid and an electromagnet? Answer: An electromagnet is a solenoid with a metal rod through the center of the coil.

Reading Skills GETTING IT ON TAPE Magnetic tape consists of a thin plastic strip bonded to a coating of ferric oxide powder. The ferric oxide, Fe2O3, makes the tape magnetizable. Early tape recorders were first developed in Germany and Britain. The first tape recorder used by the British Broadcasting Corporation in 1932 was a huge machine. It used steel razor tape that was 3 mm wide and 0.08 mm thick. The tape had to be run at 90 m/min, so the length of tape required for a half-hour program was nearly 3 km long, and a full reel had a mass of 25 kg. Furthermore, the quality of the sound experienced considerable degradation in the recording and playback process.

Reading Skills, continued GETTING IT ON TAPE, continued Higher-quality sound recording was developed in Germany during the late 1930s. During World War II, the Allies became aware of German radio broadcasts that seemed to be recorded. However, the audio quality and duration of the recordings were far greater than Allied technology would allow. At the end of the war, the Allies captured a number of German Magnetophon recorders from Radio Luxembourg, and commercial-quality magnetic recording entered the English-speaking world. 7. How is a tape coated with Fe2O3 similar to a steel wire?

Reading Skills, continued 7. How is a tape coated with Fe2O3 similar to a steel wire? Answer: Both form lines of aligned magnetizable particles.

Reading Skills, continued 8. Was the sound of a British recording during World War II better or worse after the recording was played?

Reading Skills, continued 8. Was the sound of a British recording during World War II better or worse after the recording was played? Answer: Worse

Reading Skills, continued 9. The Allies captured recording devices called magnetophons. Why is this name appropriate?

Reading Skills, continued 9. The Allies captured recording devices called magnetophons. Why is this name appropriate? Answer: Magnetophon is appropriate because it means “sound from magnetism.”

Reading Skills, continued 10. Why would bringing audiotape near a powerful magnet be a bad idea?

Reading Skills, continued 10. Why would bringing audiotape near a powerful magnet be a bad idea? Answer: The magnetizable particles will align with the magnet, erasing the tape.

Interpreting Graphics The diagram below shows an electric circuit that includes a solenoid. Use this diagram to answer questions 11–12. 11. What is the direction of the magnetic field at point X due to the current in section EF? A. into the page B. out of the page C. to the left D. to the right

Interpreting Graphics, continued 11. What is the direction of the magnetic field at point X due to the current in section EF? A. into the page B. out of the page C. to the left D. to the right

Interpreting Graphics, continued 12. To which point is the north pole of the solenoid the closest? F. A G. B H. C I. D

Interpreting Graphics, continued 12. To which point is the north pole of the solenoid the closest? F. A G. B H. C I. D

Interpreting Graphics, continued The following graphic shows four bar magnets and the magnetic fields that they generate. Use this graphic to answer questions 13–14. 13. Suppose that A and E are the north poles of their magnets. What other points have a north polarity? A. B and G B. C and H C. D and G D. D and H

Interpreting Graphics, continued 13. Suppose that A and E are the north poles of their magnets. What other points have a north polarity? A. B and G B. C and H C. D and G D. D and H

Interpreting Graphics, continued 14. Which two magnets could combine their magnetic fields into one long magnet without being rotated? What would happen to their poles?

Interpreting Graphics, continued 14. Which two magnets could combine their magnetic fields into one long magnet without being rotated? What would happen to their poles? Answer: The upper magnets could combine by connecting points B and C; B and C would lose polarity and A and D would become the poles of the new magnet.