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March 04, 2010 DRILL 1. What does the following schematic symbol represent? DC Power Supply 2. What does the following schematic symbol represent? AC Power Supply 3. 4. How many volts are typical in a residential electrical outlet? 120 volts What do graphs of DC and AC power sources look like? Why? U3e-L8 Direct Current • If voltage is constantly 1.5 V, what does its graph over time look like? 2 1 Voltage (volts) 3 1.5 V 0 2 4 6 8 10 12 14 Time (seconds) U3e-L8 Alternating Current 0 120 +/-120 V -120 Voltage (volts) • If voltage is alternating 120 V to -120 V, what does its graph over time look like? 0 2 4 6 8 10 12 14 Time (seconds) U3e-L8 Electric Motors • Michael Faraday (1791-1867) – London, England. – Physicist and Chemist • First person to successfully create an electric motor. • Discovered that electric currents create a magnetic field, and vice versa. U3e-L8 Purpose of Lesson • • To demonstrate the principle of electromagnetism. To use principles of electromagnetism to produce a mechanical result. U3e-L8 ELECTRIC MOTORS • • Electric motors are used everyday in many ways. A motor’s purpose is to turn electrical energy into mechanical energy. Motors work on simple principles of magnetism: • Opposite poles _____________ ATTRACT • Like poles _____________ REPEL N S S S N N U3e-L8 ELECTRIC MOTORS • • An electric current produces a magnetic field. Electric current through a coil of wire creates an electromagnet. • What is the benefit of creating a magnet with electricity? – It can be turned on and off. – The strength and direction of the magnetic poles can be controlled by altering the strength and direction of the electric current. U3e-L8 ELECTRIC MOTORS – What will happen now? – The electromagnet and the permanent magnet will ATTRACT each other. N S • The electromagnet and the permanent magnet will REPEL each other. S N • • Back to our magnet: Suppose we create an electromagnet like below. What will happen? U3e-L8 ELECTRIC MOTORS • • • What would happen if we put an axle through the middle of the permanent magnet, then turned on the electromagnet? This is how a motor rotates. The electromagnet is turned on and off so that the permanent magnet is attracted, then repelled, then attracted, then repelled….and so on. N S U3e-L8 ELECTRIC MOTORS What is a schematic? A schematic is a diagram that represents the elements of a system without using realistic pictures. How would a schematic which includes an electric motor look? Switch = Commutator Motor V = 9V U3e-L8 I ELECTRIC MOTORS • Now that you know what switches look like in electrical schematics, draw an electrical schematic for a lamp plugged into a wall outlet. • Remember that AC power supplies look like in electrical schematics. U3e-L8 ELECTRIC MOTORS Lamp 120 V U3e-L8 HOMEWORK • Finish reading the article about magnetism and motors (Maglev Trains) and answering the questions. • Due tomorrow. U3e-L8