Critical Thinking
Inferring Using the concept of magnetic domains, explain why a magnet will attract an iron nail but not a plastic button.
Comparing and Contrasting How does the force that an electric field exerts on a moving charged particle differ from the force exerted by a magnetic field? Assume both fields point in the same direction.
Inferring You know that if you point the thumb of your right hand in the direction of the current, your fingers curve in the direction of the magnetic field. Could you use your left hand to demonstrate this rule correctly? Explain your answer. (Hint: See Figure 7 on page 636.)
Applying Concepts A beam of electrons travels from left to right between the poles of a horseshoe magnet. The north pole is on the top, and the south pole is on the bottom. In which direction will the beam be deflected when it passes through the poles of the magnet?
Predicting Would a permanent magnet be a good core for a transformer? Explain.
Math Skills
Calculating A transformer has 20 turns in its primary coil and 60 turns in its secondary coil. The input voltage for the transformer is 25 volts. What is the output voltage?
Calculating A transformer has an input voltage of 10 volts and an output voltage of 60 volts. If the input voltage is changed to 15 volts, what will the output voltage be?
Calculating A toy train uses a step-down transformer with 500 turns on its primary coil and 50 turns on its secondary coil. If it is connected to a 120-volt line, what voltage does the toy train use?
Calculating A transformer has 12 turns on its primary coil and 60 turns on its secondary coil. If the current in the primary coil is 5 amps, what is the current in the secondary coil?
Concepts in Action
Applying Concepts In a tape recorder, the tape is coated with iron oxide that has been magnetized in patterns corresponding to sounds. To play recorded sounds, the tape moves past a tiny coil of wire. Explain how this produces an electrical signal.
Problem Solving A child's toy has a magnet hidden inside. How can you determine where the north and south poles of the magnet are, without damaging the toy?
Applying Concepts A power plant generates electricity at 1200 volts. The electricity is transmitted at 180,000 volts and then reduced to 2400 volts at a substation. Finally, it is reduced to 120 volts for use in a home. For each transformer, describe the ratio of the number of turns in the primary and secondary coils.
Inferring Credit cards have a magnetic strip on them that contains information in a pattern. When a cashier runs the card through a card reader, the magnetic strip passes by a small wire coil. Why is motion necessary for the coil to read the card?
Writing in Science Write a paragraph explaining why alternating current is used for power generation and distribution instead of direct current.
Performance-Based Assessment
Creating an Educational Booklet Write a booklet for elementary students describing how electricity is brought from the power plant to their homes. Include simple illustrations and caution statements that young children can understand.
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