According to electronic theory, the electron is responsible for a flow of current of electricity.
Good conductors are considered to be those substances in which there are present free electrons in constant but indiscriminate motion between the atoms. Under the action of an electromotive force, these free electrons move in some definite direction, resulting in a constant stream of electrons flowing at a phenomenally rapid rate in the conductor. In the case of a uni-directional or direct current, this electronic stream is always in one direction, while with alternating current the electronic stream reverses its direction of motion with regular frequency. All pure metals are good conductors of electricity, silver being the best since it offers the least resistance to a flow of current of electricity. We know copper to be very nearly as good a conductor as silver and, being very much cheaper, it is extensively used for electrical apparatus of all kinds. It is universally employed in all automobile electrical equipment.
Roughly speaking a conductor is a body which readily permits the passage of an electric current, an insulator being a body which offers a very high resistance to the passage of the current. As a matter of fact, there is no sharp distinction between conductors and insulators, however, a material which for some cases would be regarded as an insulator would, in other circumstances, be regarded as a conductor. A substance which is a good insulator at law temperatures may be a fair conductor at high temperatures.
II. Answer the following questions.1.What is responsible for a flow of current of electricity?
2. What substances are considered to be good conductors of electricity?
3. When do free electrons move in some definite direction and what is the result of this movement?
4. What is the stream of electrons both in a direct and alternating current?
5. At what frequency does the electronic stream reverse its direction of motion?
6. What are the best conductors of electricity?
7. What is an insulator?
8. Is there any sharp distinction between conductors and insulators?
III. Read the statement. Decide whether that sentence is true or false.1. The best conductors are silver and copper.
2. Copper isn’t used to produce wire conductors.
3. Metals increase the resistance when the temperature increases.
4. Conductors are materials having a low resistance.
5. Insulators are materials having a low resistance.
IV. Continue the sentences.1. Good conductors are considered to be those substances in ____________________________
2. Under the action of an electromotive force, these free electrons move in _________________
3. All pure metals are good conductors of electricity, silver being ________________________
4. We know copper to be very nearly as good a conductor as silver and ___________________
5. As a matter of fact, there is no sharp distinction between _____________________________