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# solution8_pdf - hussain(wh4892 hw 8 Opyrchal(121104 This...

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hussain (wh4892) – hw 8 – Opyrchal – (121104) 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points Consider the following circuit. 7 . 2 Ω 3 . 4 Ω 3 . 4 Ω 4 . 2 Ω 1 . 9 Ω 3 . 4 Ω 4 . 2 Ω 15 . 0 Ω 15 . 0 Ω 34 V a) Find the equivalent resistance. Correct answer: 17 . 956 Ω. Explanation: R 1 R 4 R 7 R 3 R 6 R 9 R 8 R 5 R 2 Δ V Let : R 1 = 7 . 2 Ω , R 2 = 15 . 0 Ω , R 3 = 4 . 2 Ω , R 4 = 3 . 4 Ω , R 5 = 15 . 0 Ω , R 6 = 1 . 9 Ω , R 7 = 3 . 4 Ω , R 8 = 4 . 2 Ω and R 9 = 3 . 4 Ω . For resistors in series, R eq,s = R a + R b R 789 = R 7 + R 8 + R 9 = 3 . 4 Ω + 4 . 2 Ω + 3 . 4 Ω = 11 Ω . For resistors in parallel, 1 R eq,p = 1 R a + 1 R b R 5789 = parenleftbigg 1 R 5 + 1 R 789 parenrightbigg 1 = parenleftbigg 1 15 Ω + 1 11 Ω parenrightbigg 1 = 6 . 34615 Ω , R 456789 = R 4 + R 5789 + R 6 = 3 . 4 Ω + 6 . 34615 Ω + 1 . 9 Ω = 11 . 6462 Ω , R 2456789 = parenleftbigg 1 R 2 + 1 R 456789 parenrightbigg 1 = parenleftbigg 1 15 Ω + 1 11 . 6462 Ω parenrightbigg 1 = 6 . 556 Ω , and R eq = R 1 + R 2456789 + R 3 = 7 . 2 Ω + 6 . 556 Ω + 4 . 2 Ω = 17 . 956 Ω . 002 (part 2 of 2) 10.0 points b) Find the current in the 7 . 2 Ω resistor. Correct answer: 1 . 89352 A. Explanation: Let : Δ V = 34 V Δ V = IR = I 1 = I I 1 = Δ V R eq = 34 V 17 . 956 Ω = 1 . 89352 A . 003 (part 1 of 3) 10.0 points A circuit contains six 220 Ω lamps and a 10 Ω heater connected in parallel. The voltage across the circuit is 139 V. What is the current in the circuit when four lamps are turned on? Correct answer: 2 . 52727 A. Explanation:

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hussain (wh4892) – hw 8 – Opyrchal – (121104) 2 Let : R l = 220 Ω , R h = 10 Ω , and V = 139 V . For the parallel circuit, the voltage is the same across each branch and the currents add up. Thus each branch receives V volts so that the current for each lamp is I l = V R 1 . With 4 lamps in the circuit, I = 4 I l = 4 V R l = 4 (139 V) 220 Ω = 2 . 52727 A . 004 (part 2 of 3) 10.0 points What is the current when all lamps are on? Correct answer: 3 . 79091 A. Explanation: With six lamps in the circuit, I 2 = 6 I l = 6 V R l = 6 (139 V) 220 Ω = 3 . 79091 A . 005 (part 3 of 3) 10.0 points What is the current if six lamps and the heater are operating? Think about this situation with a 12 A fuse in the line.
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