Electricity I Notes

An electric current is generated when a coil of wire is moved in a magnetic field. This is called induction, and is the way that electric power plants, such as LP&L, generate electricity. The rotating coils of wire are usually on the shaft of a device called a steam turbine. A steam turbine is a type of steam engine in which entering steam pushes against the engine blades causing the blades and the shaft to which they are connected to rotate. As the blades turn, the coil of wire rotates in the magnetic field.

Most electric current is produced by steam. Water is heated to produce this steam which forces the blades of the turbine to rotate. The steam becomes liquid water and is re-heated to again produce steam. The heat to convert water to steam usually comes from burning fossil fuels, such as coal, oil or natural gas. However, nuclear fission can also be used to produce the heat needed to convert water to steam.

Although most electric current is generated by steam turbines, there are other less frequently used methods. These include hydroelectric generators which use falling water to turn the blades of a turbine, solar powered generators which use mirrors to focus the heat of sunlight to convert water to steam, and wind power.

Nuclear fission is a good way to heat water to run the steam turbines. However, there are problems. These include the high cost of building a nuclear reactor, how to dispose of the nuclear waste, and the fear of a core melt down. The fuel which is used to power a nuclear power plant is uranium 235. When uranium atoms are split, heat is released which is used to heat water. In a melt down, the uranium fuel over-heats melting its casing and is released into the environment. This radioactive material can do bad things, like cause cancer and produce genetic defects. The uranium fuel core is cooled by water pumped through a series of pipes inside a thick concrete and steel casing. If there is a failure in this system, melt down can occur. Methods being considered to prevent melt down include using uranium pellets the size of a grain of sand coated in heat resistant ceramic material, and the use of helium gas to cool the core rather than water. A reactor using uranium pellets could be used to produce a uranium by-product called tritium. Tritium is used to make nuclear weapons.

Another method of producing electricity is the thermocouple. A thermocouple is a device that changes heat energy into electricity. Contact between metals that are at different temperatures causes a flow of electrons. Thermocouples produce small amounts of electricity. They are often used to activate safety shutoff devices in furnaces and in automobile engines.

Another method of generating electricity is the solar cell. Elements such as selenium, silicon and germanium release electrons when exposed to light. These elements are used to construct solar cells. The solar cells release electrons when exposed to sunlight. Solar cells are used to recharge the batteries found in solar powered calculators. The main limitation to solar cells is they generate very small amounts of electricity.

After electric current has been generated, it must be transported to the consumer. Electric current cannot be stored, so it must be constantly produced. Electricity is most efficiently transported at high voltage, low amps. To increase the voltage, as soon as electricity is produced it goes to a step-up transformer. The step-up transformer increases the voltage for transportation over long distances. It is often stepped-up as high as 500,000 volts. When the electricity arrives at its destination, it goes to a step-down transformer, which lowers the voltage to usable levels. Transformers step-up and down voltage through induction.

Faraday discovered that an alternating current in one circuit will induce an alternating current in another circuit. This is the principle on which a transformer is based. A transformer will only work on alternating current (A.C.). It will not work on direct current (D.C.) A transformer consist of two coils of insulated wire wrapped around the same iron core. One coil is called the primary coil. The primary coil delivers the electric current to the iron core. The other coil is the secondary coil. Electric current is induced in the secondary coil. If the number of loops in the primary and secondary coils are equal, the induced voltage in the secondary coil will be the same as that of the primary coil. If, however, there are more loops in the secondary coil than in the primary coil, the voltage in the secondary coil will be greater than the voltage of the primary coil. This is a step-up transformer. If there are more loops in the primary coil than in the secondary coil, the voltage in the secondary coil will be less than the voltage in the primary coil. This is a step-down transformer.

Electricity Study Sheet