CHAPTER 21 Study Guide

21.1 Magnets and Magnetic Fields

Key Concepts

• Like magnetic poles repel one another, and opposite magnetic poles attract one another.

• A magnetic field, which is strongest near a magnet's poles, will either attract or repel another magnet that enters the field.

• When a material is magnetized, most of its magnetic domains are aligned.

Vocabulary

• magnetic force, p. 630

• magnetic pole, p. 630

• magnetic field, p. 631

• magnetosphere, p. 632

• magnetic domain, p. 632

• ferromagnetic material, p. 632

21.2 Electromagnetism

Key Concepts

• Moving electric charges create a magnetic field.

• Changing the current in an electromagnet controls the strength and direction of its magnetic field.

• Electromagnetic devices such as galvanometers, electric motors, and loudspeakers change electrical energy into mechanical energy.

Vocabulary

• electromagnetic force, p. 635

• solenoid, p. 637

• electromagnet, p. 637

• galvanometer, p. 638

• electric motor, p. 639

21.3 Electrical Energy Generation and Transmission

Key Concepts

• According to Faraday's law, a voltage is induced in a conductor by a changing magnetic field.

• The two types of generators are AC generators and DC generators.

• A transformer changes voltage and current by inducing a changing magnetic field in one coil. This changing field then induces an alternating current in a nearby coil with a different number of turns.

• Most of the electrical energy generated in the United States is produced using coal as an energy source. Some other sources are water (hydroelectric), nuclear energy, wind, natural gas, and petroleum.

Vocabulary

• electromagnetic induction, p. 642

• generator, p. 643

• transformer, p. 644

• turbine, p. 646

Thinking Visually

Concept Map Copy the concept map below onto a sheet of paper. Use information from the chapter to complete the chart.

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