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Unformatted text preview: Questions W denotes answer available in Student Solutions Manual/Study Guide; O denotes objective question 1. Newspaper articles often contain a statement such as “10 000 volts of electricity surged through the victim’s body.’’ What is wrong with this statement? 2. What factors affect the resistance of a conductor? 3. O Two wires A and B with circular cross sections are made of the same metal and have equal lengths, but the resistance of wire A is three times greater than that of wire B. (i) What is the ratio of the cross- sectional area of A to that of B? (a) 9 (b) 3 (c) 3 (d) 1 (e) 1/ 3 (f) 1/3 (g) 1/9 (h) None of these answers is necessarily true. (ii) What is the ratio of the radius of A to that of B? Choose from the same possibilities. 4. O A metal wire of resistance R is cut into three equal pieces that are then braided together side by side to form a new cable with a length equal to one-third the original length. What is the resistance of this new wire? (a) R /27 (b) R /9 (c) R /3 (d) R (e) 3 R (f) 9 R (g) 27 R 5. When the potential difference across a certain conductor is doubled, the current is observed to increase by a factor of three. What can you conclude about the conductor? 6. Use the atomic theory of matter to explain why the resistance of a material should increase as its temperature increases. 7. O A current-carrying ohmic metal wire has a cross- sectional area that gradually becomes smaller from one end of the wire to the other. The current has the same value for each section of the wire, so charge does not accumulate at any one point. (i) How does the drift speed vary along the wire as the area becomes smaller? (a) It increases. (b) It decreases. (c) It remains constant. (ii) How does the resistance per unit length vary along the wire as the area becomes smaller? Choose from the same possibilities. 8. How does the resistance for copper and for silicon change with temperature? Why are the behaviors of these two materials different? 9. Over the time interval after a difference in potential is applied between the ends of a wire, what would happen to the drift velocity of the electrons in a wire and to the current in the wire if the electrons could move freely without resistance through the wire? 10. If charges flow very slowly through a metal, why does it not require several hours for a light to come on when you throw a switch? 11. O A cylindrical metal wire at room temperature is carrying electric current between its ends. One end is at potential V A = 50 V, and the other end at potential V B = 0 V. Rank the following actions in terms of the change that each one separately would produce in the current, from the greatest increase to the greatest decrease. In your ranking, note any cases of equality....
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- Summer '08
- Physics, Potential difference, Electric charge, Electrical conductor, Electrical conductivity