Producing Electric Current Section 8.3: Physical Science

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

Electromagnetic induction & Generators 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

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

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

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

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

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

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

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