Producing Electric Current

1. Producing Electric Current Section 8.3: Physical Science

2. From Mechanical to Electrical Energy • A magnet can produce an electric current- • Moving a loop of wire through a magnetic field causes electric current to flow in the wire • Moving a magnet through a loop of wire has the same effect • http://micro.magnet.fsu.edu/electromag/java/faraday2/ • How can a magnet produce a current in a wire? • ME due to the motion of the wire or magnet is converted to electrical energy

3. Electromagnetic induction & Generators • Electromagnetic Induction • Producing an electric current by moving a loop of wire through a magnetic field or moving a magnet through a wire loop • Generators • Machines that produce electric current by rotating a coil of wire in a magnetic field • Wire coil is wrapped around an iron core and placed between the poles of a permanent magnet. • http://www.walter-fendt.de/ph11e/generator_e.htm

4. Generators • Coil is rotated by an outside source of mechanical energy • Examples: Steam, wind, water • As the coil turns in the magnetic field, electric current flows through the wire • When the coil turns so that the ends move past opposite ends of the magnet: • The current reverses direction • The current changes direction twice with each revolution • A generator that is used in a car is known as an alternator

5. Electric Generators • Electricity in the home comes from a power plant with huge generators • When the coil is fixed and the magnet rotates, the current is the same as if the coil rotates and the magnet is fixed. • Construction of a generator in a power plant • Electromagnets contain coils of wire wrapped around iron cores • Rotating magnets connect to a turbine • Turbine: large wheel that rotates due to • Hoover Dam and Hydroelectric Power • Sources of electricity: http://www.teachersdomain.org/resources/phy03/sci/phys/energy/energysource/index.html

6. Direct and Alternating Currents • Compare and contrast current in batteries and generators: • Compare: Both devices move electrons through the wire • Contrast: Batteries have DC. Generators have AC. • DC- Direct Current- Flows in only one direction. • AC- Alternating current- reverses the direction of current flow regularly. • In N America, generators produce alternating current at a frequency of 60 cycles per second, or 60 Hz • A 60-Hz alternating current changes direction 120 times per second

7. Alternating Current • http://schoolforchampions.com/science/ac.htm

8. Transformers • To make electric energy safe for your home you must: • Use a transformer- increases or decreases voltage • Transformers are made up of 2 coils (primary and scondary_ wrapped around an iron core. • Alternating current in a primary coil creates a changing magnetic field around the iron core, which induces an alternating current in the secondary coil

9. Transformers • Step – up transformer increases voltage. The secondary coil has more turns than the primary coil does • Step-down transformer decreases voltage. The secondary coil has fewer turns than the primary coil does • http://www.school-for-champions.com/science/ac_transformers.htm

10. Electricity • Power carried in power lines as high as 750,000 volts is reduced by step-down transformers to household current (AC) of 120V • What happens to electrical energy as it passes through a wire? • Some is lost as heat due to resistance of the wire • Why is electrical energy transmitted at high voltages? • To prevent loss of energy as heat