http://www.ck12.org Chapter 21. Electromagnetic Induction
CHAPTER
21 Electromagnetic Induction
Chapter Outline
21.1 Electromotive Force
21.2 ELECTRICGENERATORS
21.3 LENZ’SLAW
21.4 Transformers
21.5 References
If you have ever looked at above ground distribution electric power lines, you have surely seen barrel shaped devices
attached to various power poles. These barrel shaped devices are called transformers and their purpose is to change
the form of the electric power. All metal transmission wires have some amount of resistance to the passage of
electric current. The result of forcing electric current through the resistance is that some of the electric power is
converted to heat and the energy lost to the surroundings. The amount of energy lost is proportional to the square
of the electric current.
The electric power transmitted over these lines can be calculated in watts and is equal to the voltage times the
amperage of the current. If you transmitted 100 amps with a voltage of 50,000 volts, the power transmitted would
be 5,000,000 watts. This same amount of power could be transmitted by using an electric current of 5 amps and a
voltage of 1,000,000 volts.
Since the energy lost to heat is related to the square of the amps, using the 5 amp current instead of the 100 amp
current would make a tremendous difference in the energy lost. Therefore, it is clearly wise to increase the voltage of
the current and reduce the amperage before sending the current over the long transmission lines. When the electric
current reaches houses and factories and other places where the electricity will be used, the appliances cannot use
a current of 5 amps with a voltage of 1,000,000 volts. Therefore, the electric current must be transformed to some
form of electric current that households can use.