Act17_sol - Period 17 Activity Solutions: Induction Motors...

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65 Period 17 Activity Solutions: Induction Motors and Transformers Activity 17.1: How Can Current Be Induced in a Closed Circuit? a) Connect the tan coil of wire to the large galvanometer that measures electric current. Move a magnet near and into the wire coil. Describe what happens. A current is induced in the wire when the magnet moves near to and into the coil of wire. The galvanometer measures this current. b) Hold the magnet still and move the coil of wire. Describe what happens. The galvanometer again measures current flowing through the wire. The direction of current flow depends on the direction the wire moves relative to the magnet. c) What happens if neither the magnet nor the wire is moving? No current flows. One (either the magnet or the wire) must be moving. Activity 17.2: How Do Generators Work? a) Attach a hand-cranked generator to a small motor and turn the crank. Explain what happens inside the generator when the crank turns to create a current. The crank spins a coil of wire relative to a magnet located inside the generator. This movement causes the wire to experience a changing magnetic field, which induces current in the wire. b) List the energy conversions that take place when you crank the generator and make the motor’s shaft turn. The chemical energy (of your body) kinetic energy of the moving coil electrical energy kinetic energy of the moving motor shaft c) Connect one hand-cranked generator to a second hand-cranked generator and make the second generator spin. How is this activity similar to a generating plant? How is it similar to a motor? Both motors and generators use changing magnetic fields. Motors convert electrical energy into kinetic energy, while generators convert kinetic energy into electrical energy. Generators use kinetic energy to spin coils of wire near magnets, creating a changing magnetic field. The changing field induces a current in the wires. Motors use a changing electric current to produce a changing magnetic field, which spins a rotor by attracting and repelling it. Activity 17.3: Is Induced Current Alternating or Direct Current? a) Move a magnet into and out of the small coil of wire with red and green bulbs attached. How must you move the magnet so that the red bulbs light and then the green bulbs light? When you move the magnet into the coil one color of bulb lights, and when you move the magnet out of the coil the other color of bulb lights. The lights are designed to respond to current moving in one direction only. Thus, the red lights go on when the current flows in one direction, and the green lights go on when the current flows in the opposite direction.
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66 b) Is the current that you induce as you move the magnet in and out of the coil direct current (DC) or alternating current (AC)? _ AC _ How do you know? When you change direction of the motion of the magnet, you create a
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Act17_sol - Period 17 Activity Solutions: Induction Motors...

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