hw13-solutions - Reilly (mar3978) hw13 turner (56725) 1...

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Unformatted text preview: Reilly (mar3978) hw13 turner (56725) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A variable resistor is connected across a con- stant voltage source. Which of the following graphs represents the power P dissipated by the resistor as a function of its resistance R ? 1. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 2. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 3. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 4. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 5. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) correct 6. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 7. 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) Explanation: The power dissipated in the resistor has several expressions P = E I = E 2 R = I 2 R, where the last two are simply derived from the first equation together with the application of the Ohms law. Since the resistor is connected to a constant voltage source E = constant P = E 2 R = constant R , tells us that the power is inversely propor- tional to the resistance parenleftbigg P 1 R parenrightbigg . 0 1 2 3 4 5 6 7 8 910 1 2 3 4 5 Resistance () Power(W) 002 (part 1 of 3) 10.0 points A 1120 resistor is rated at 4 . 82 W. What is the maximum current through this resistor? Correct answer: 0 . 0656016 A. Explanation: Let : R = 1120 and P = 4 . 82 W . Reilly (mar3978) hw13 turner (56725) 2 The power rating of the resistor is the maxi- mum allowed power dissipation of the resistor and corresponds to a maximum current. P = I V = I 2 R I = radicalbigg P R = radicalbigg 4 . 82 W 1120 = . 0656016 A . 003 (part 2 of 3) 10.0 points If the maximum current has been passing through the resistor for 25 . 1 minutes, how many Coulombs of charge passes through the resistor in this period? Correct answer: 98 . 796 C. Explanation: Let : t = 25 . 1 minutes . Current is I = Q t Q = I t = (0 . 0656016 A) (25 . 1 minutes) parenleftbigg 60 s min parenrightbigg = 98 . 796 C . 004 (part 3 of 3) 10.0 points Denote the amount of charge in part 2 by Q . Consider the passage of the same maxi- mum current as in Part 2 through two 1120 resistors connected in series. How much charge passes through any cross section in this resistor series in 25 . 1 minutes? 1. Q = 2 Q 2. Q = Q 2 3. Q = Q 4 4. Q = 4 Q 5. Q = 2 Q 6. None of these 7. Q = Q 2 8. Q = Q correct Explanation: Since Q = I T , then when I is fixed and T is fixed, Q is correspondingly fixed. So Q = Q . 005 10.0 points We estimate that there are 268 million plug-in electric clocks in the United States, approxi- mately one clock for each person. The clocks convert energy at the average rate of 9 . 2 W....
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hw13-solutions - Reilly (mar3978) hw13 turner (56725) 1...

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