Producing Electric Current Section 8 3 Physical Science

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/farad ay 2/ �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 �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/ph 11 e/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/phy 03/sci/phys/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-forchampions. 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 120 V �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