Comprehension check
Date: 2015-10-07; view: 542.
14. Use the text to answer the following questions:
1. What is called an electric current?
2. What is resistance?
3. What factors affect electrical resistance?
4. What is resistivity?
5. How can the resistance of a conductor be determined if its length, material and cross-section are known?
6. Define ohm.
7. What materials have low resistance?
8. Does the resistance of metals increase with increasing temperature?
9. Is the resistance of manganin affected by temperature rise?
15. Put the jumbled sentences in the logical order to sum up the contents of the text.
1. The flow of electrons in a conductor is called an electric current.
2. There are several factors that affectresistance.
3. The resistance of most metals varies directly with temperature.
4. That is, temperature being constant, the resistance will be doubled if the length of the conductor is doubled.
5. If two metal spheres on insulating supports are charged with unlike electricity (say, sphere A positively and sphere B negatively) and connected by a metal conductor, electrons will flow from B, where they are in excess, to A where they are lacking.
6. The unit of electrical resistance is the ohm.
7. The resistance of a conductor increases in direct proportion with its length.
8. As a result, energy is released in the form of heat, and the motion of electrons along the conductor is impeded.
9. The resistance in ohms of a conductor 1 metre long and 1 mm2 in cross-section is called resistivity and is designated by the Greek letter p (rho).
10. Resistance varies with the atomic structure or nature of the conducting material.
11. The change in the resistance of a conductor per ohm of the initial resistance and per degree change of temperature is termed the temperature coefficient of resistance and is designated by the letter a
12. The resistance of metals increases with increasing temperature, while that of liquids and carbon decreases.
13. The resistance of the conductor varies inversely with its cross-section area.
14. This opposition to the motion of electrons along the conductor is known as the electrical resistance of the conductor.
15. While in motion along a conductor, electrons collide with other electrons, atoms or molecules.
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