# HW8soln - P = 50 W bulb R = V 2 P =(D How much current does...

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Physics 21 Fall 2007 Solution to HW-8 25.2 A silver wire 2.6 mm in diameter transfers a charge of 420 C in 80 minutes. Silver contains 5.8 x 10 28 free electrons per m 3 . (A) What is the current in the wire? (B) What is the magnitude of the drift velocity of the electrons in the wire? 25.32 Consider the circuit shown in the figure. The terminal voltage of the 24 volt battery is 21.2 volts. The current in the circuit is 4.00 A. (A) What is the internal resistance r of the battery? What is the resistance R of the circuit resistor? 24 V r R 4.0 A 25.43 The power rating of a light bulb (such as a 100 W bulb) is the power it dissipates when connected across a V = 120 volt potential difference. (A) What is the resistance of a bulb with P = 100 W? P = IV ==> I = P/V P = I 2 R ==> R = P/I 2 = P ( V/P ) 2 = V 2 / P = 144 \Omega (B) How much current does the P = 100 W bulb draw in normal use? I = P/V (C) What is the resistance of a
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Unformatted text preview: P = 50 W bulb? R = V 2 / P = (D) How much current does the P = 50 W bulb draw in normal use? I = P/V OE 41-1 In the circuit shown in the figure, (A) what is the value of the current I 1 ? (B) What is the value of the current I 2 ? (C) What is the value of the current I 3 ? 26.6 For the circuit shown in the figure both meters are idealized; the battery has no appreciable internal resistance, and the ammeter reads 1.45 A. (A) What does the voltmeter read? (B) What is the emf E of the battery? 25.72 A typical cost for electric power is \$0.12 per kilowatt-hour. (A) Some people leave their porch light on all the time. What is the yearly cost to keep a 90 W bulb burning day and night? (B) Suppose your refrigerator uses 500 W of power when it's running, and it runs 8 hours per day. What is the yearly cost of operating your refrigerator? I 1 I 3 I 2...
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