Act16_sol(1) - Period 16 Activity Sheet Solutions Motors...

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61 Coil of wire Period 16 Activity Sheet Solutions: Motors 16.1 How Do Direct Current (DC) Electric Motors Work? a) Spinning rotors. In this activity, we see why the rotor of an electric motor spins. 1) Place a permanent magnet on a plastic spinner and make the magnet spin by holding another magnet nearby. The magnets simulate a motor. Could you make a practical motor using only permanent magnets? Explain why or why not. It would not be practical. A changing magnetic field is required to spin the rotor. To create a changing field using only permanent magnets, one magnet must continuously be moved to keep the second magnet spinning. 2) Place a solenoid near the magnet on the spinner. Make the magnet spin by alternately connecting and disconnecting the solenoid from a 3 battery tray. Could you make a practical motor using electromagnets (like the solenoid) and a continuous, unchanging current? Explain why or why not. No, a motor requires a changing magnetic field. A continuous current, such as the direct current from a battery, produces an unchanging magnetic field. 3) What type of current is required to make a motor run? _ a changing current_ Activity 16.2: How Can You Make a Simple Motor? a) Building the motor. Refer to the model on your table. 1) Cut a 3 meter length of coated wire. 2) Wrap the wire into a circle 3 to 4 cm in diameter, leaving about 4 cm of wire protruding from each side of the circle. 3) Use sandpaper to carefully scrape the coating off of one side of one end of the protruding wire. Scrape all of the coating off of the other end of the wire. 4) Place the wire circle on a paper clip support stapled to a wooden block. 5) Use connecting wires to attach the positive end of a 3 battery tray to one side of the metal support and the negative end to the other side of the support. 6) Hold a strong magnet near the coil of wire and start the coil spinning with your finger. b) How does the motor work? 1) Why must you scrape the coating off of the ends of the wire? Why do you scrape it from only one side of one of the ends? End view of wire with coating scraped from one side of one end. Coating Wire
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62 Scraping coating off of the wire is necessary to make a conducting pathway. If there is coating on only one side of one end of the wire, the conducting pathway is connected and disconnected as the wire spins, turning the current on and off. 2) What provides a changing magnetic field in this motor? Current flowing through the coil of wire during one half of the turn creates a changing magnetic field that is attracted the permanent magnet. During the second half of the turn, when the side of the wire with insulation is touching the support, the current is off and the coil of wire has no magnetic field.
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