# hw12 - Solution for Homework 12 Kirchhoffs Laws Solution to...

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Unformatted text preview: Solution for Homework 12 Kirchhoffs Laws Solution to Homework Problem 12.1(Voltage Across a Device in a Series Circuit Given the Voltage Across the Other Device and the Battery) Problem: Two devices are connected in a series circuit with a 9V battery. The voltage across the first device is 2V . What is the voltage across the second device? Select One of the Following: (a) 2V (b-Answer) 7V (c) 9V (d) 11V (e) Cannot be determined unless the resistances are known. Solution In a series circuit, the total potential drop across the devices must be equal to the potential gain across the battery. The potential gain across the battery is the same as the voltage of the battery: 9V . The given potential drop across the first device is 2V . The potential drop across the remaining device is then equal to 9V- 2V = 7V . Total Points for Problem: 3 Points Solution to Homework Problem 12.2(What part of electricity do you pay for?) Problem: When you pay your household electric bill at the end of the month, which of the following are you paying for? Select One of the Following: (a) Voltage (b) Current (c) Power (d-Answer) Energy (e) None of the above. Solution Energy. Total Points for Problem: 3 Points Solution to Homework Problem 12.3(Voltage Across Parallel Resistor) 1 Problem: In the resistance network to the right all resistors are 2 and the battery is 6V Calculate the potential difference across R 3 . Select One of the Following: (a-Answer) 6 5 V (b) 8 5 V (c) 3V (d) 2V (e) 6V R 1 R 3 R 2 R 4 Solution The equivalent resistance of the parallel circuit is 1 R p = 1 R 2 + 1 R 3 or R p = 1 . The equivalent circuit with the parallel resistor reduced is drawn to the right. The equivalent resistance of the full circuit is then R eq = R 1 + R + p + R 4 = 5 . The current drawn by the circuit is then I = V/R eq = 6 5 A . The potential difference across R p is then V p = IR p = 6 5 V . This is the same potential difference that exists across R 3 . R 1 R 4 R p Total Points for Problem: 3 Points Solution to Homework Problem 12.4(The Change in the Reading of a Voltmeter When a Switch is Closed) 2 Problem: When the switch is closed, what happens to the reading of the voltmeter? Select One of the Following: (a-Answer) The reading will increase. (b) The reading will decrease. (c) The reading will stay the same. V Solution (a) When the switch is closed, the equivalent resistance of the parallel combination decreases, and therefore the equivalent resistance of the circuit decreases....
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## hw12 - Solution for Homework 12 Kirchhoffs Laws Solution to...

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