美国（USA）高中物理教材原理与问题第二十五章.pdfVIP

What You’ll Learn • You will describe how changing magnetic fields can generate electric potential differences. • You will apply this phenomenon to the construction of generators and transformers. Why It’s Important The relationship between magnetic fields and current makes possible the three cornerstones of electrical technology: motors, generators, and transformers. Hydroelectric Generators Dams commonly are built on rivers to provide a source of power for nearby communities. Within the dam, the potential and kinetic energy of water is turned into electric energy. Think About This How do the generators located inside the dam convert the kinetic and potential energy of the water into electric energy? 670 Tom Pantages, (inset)Robert Cameron/Getty Images What happens in a changing magnetic field? Question How does a changing magnetic field affect a coil of wire passed through it? Procedure 1. Place two bar magnets about 8 cm apart. 2. Attach a sensitive galvanometer to either end of a piece of coiled copper wire. 3. Slowly move the wire between the magnets. Note the galvanometer reading. 4. Vary the angle of the movement of the copper wire and the velocity of the wire. Note your results. Analysis What causes the galvanometer to move? What situation makes the galvanometer deflect the most? Critical Thinking When the wire is moved between the magnets, what is happening to the wire? 25.1 Electric Current