Qwizdom questions for Jan. 15, 2010

21. One coulomb per volt is a A.joule B.electron-volt C. farad D. watt

21. The correct answer is C, farad. For a capacitor: C = Q/V

22. A dielectric material such as paper is placed between the plates of a capacitor. What happens to the capacitance? A. no change B. becomes larger C. becomes smaller

22. The answer is B, the capacitance increases. Recall that The dielectric constant, K = 3.7 for paper.

23. Doubling the voltage across a given capacitor causes the energy stored in that capacitor to A. quadruple B. double C. reduce to one half D. reduce to one fourth

23. The answer is A, the energy quadruples. So if V is doubled, U will be four times as large.

24. Consider two copper wires. One has twice the cross-sectional area of the other. How do the resistances of these two wires compare? A. Both wires have the same resistance. B.The thicker wire has half the resistance of the thinner wire. C.The thicker wire has twice the resistance of the thinner wire.

24. The correct answer is B since and the thicker wire has a larger cross- sectional area.

25. A kilowatt-hour is equivalent to A W B s C. 3,600,000 J/s D. 3.6 MJ

25. The correct answer is D.

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