electric conductors and insulators
the path of least resistance
Look at the electric wires in the Figure 1.1. They are made of copper and coated with plastic. Copper is very good conductor, and plastic is a very good insulator. When more than one material is available for electric current to flow through, the current always travels through the material with the least resistance. Thats why all the current passes through the copper wire and none flows through its plastic coating.
Materials that have low resistance to electric current are called electric conductors. Many metalsincluding copper, aluminum, and steelare good conductors of electricity. The outer electrons of metal atoms are loosely bound and free to move, allowing electric current to flow. Water that has even a tiny amount of impurities is an electric conductor as well. Q: What do you think lightning rods are made of? A: Lightning rods are made of metal, usually copper or aluminum, both of which are excellent conductors of electricity.
Materials that have high resistance to electric current are called electric insulators. Examples include most non- metallic solids, such as wood, rubber, and plastic. Their atoms hold onto their electrons tightly, so electric current cannot flow freely through them. Dry air is also an electric insulator. Q: You may have heard that rubber-soled shoes will protect you if you are struck by lightning. Do you think this is true? Why or why not? A: It isnt true. Rubber is an electric insulator, but a half-inch layer on the bottom of a pair of shoes is insignificant when it comes to lightning. The average lightning bolt has 100 million volts and can burn through any insulator, even the insulators on high-voltage power lines.
electric current and matter
Electrical energy is transmitted by moving electrons in an electric current. In order to travel, electric current needs matter. It cannot pass through empty space. However, matter resists the flow of electric current. Thats because flowing electrons in current collide with particles of matter, which absorb their energy. Some types of matter offer more or less resistance to electric current than others.
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electric current can travel across space as well as through matter.
a. true --> b. false
examples of materials that have low resistance to electric current include
--> a) water containing impurities. b) rubber. c) plastic. d) all of the above
examples of materials that have high resistance to electric current include
--> a) wood. b) steel. c) copper. d) two of the above
electric current always travels through the material of least resistance.
--> a. true b. false
dry air is an electric insulator.
--> a. true b. false
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