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oldhw16 - oldhomewk 16 LEE BENJAMIN Due Oct 9 2007 4:00 am...

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oldhomewk 16 – LEE, BENJAMIN – Due: Oct 9 2007, 4:00 am 1 Question 1, chap 28, sect 8. part 1 of 4 10 points A 154 Ω lamp, a 21 Ω electric heater, and a 45 Ω fan are connected in parallel across a 135 V line. What total current is supplied to the cir- cuit? Correct answer: 10 . 3052 A (tolerance ± 1 %). Explanation: Let : R 1 = 154 Ω , R 2 = 21 Ω , R 3 = 45 Ω , and V = 135 V . For the parallel circuit, 1 R = 1 R 1 + 1 R 2 + 1 R 3 = R 1 R 2 + R 2 R 3 + R 3 R 1 R 1 R 2 R 3 R = R 1 R 2 R 3 R 1 R 2 + R 2 R 3 + R 3 R 1 R 1 R 2 + R 2 R 3 + R 3 R 1 = (154 Ω) (21 Ω) + (21 Ω) (45 Ω) + (45 Ω) (154 Ω) = 11109 Ω 2 , so R = (154 Ω) (21 Ω) (45 Ω) 11109 Ω 2 = 13 . 1002 Ω and I = V R = 135 V 13 . 1002 Ω = 10 . 3052 A . Question 2, chap 28, sect 8. part 2 of 4 10 points What is the voltage across the fan? Correct answer: 135 V (tolerance ± 1 %). Explanation: Because the circuit elements are connected in parallel, the voltage across the fan is the same as that across the whole circuit. Question 3, chap 28, sect 8. part 3 of 4 10 points What is the current in the lamp? Correct answer: 0 . 876623 A (tolerance ± 1 %). Explanation: The voltage is the same in all 3 appliances, so the current through the lamp is I 1 = V R 1 = 135 V 154 Ω = 0 . 876623 A . Question 4, chap 28, sect 8. part 4 of 4 10 points What power is expended in the heater? Correct answer: 867 . 857 W (tolerance ± 1 %). Explanation: The power consumed by the heater is P 2 = V 2 R 2 = (135 V) 2 21 Ω = 867 . 857 W . Question 5, chap 30, sect 1. part 1 of 4 10 points A particle of mass m and charge q starts from rest at the origin (point A in the figure below). E B A C G X Y B There is a uniform electric field vector E in the pos- itive y -direction and a uniform magnetic field vector B directed towards the reader. It can be shown that the path is a cycloid whose ra- dius of curvature at the top point is twice the y -coordinate at that level.

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oldhomewk 16 – LEE, BENJAMIN – Due: Oct 9 2007, 4:00 am 2 What is the relation between kinetic energy of the charge at points A and B ? 1. The kinetic energy of the particle at point B is the same as it was at point A . correct 2. The kinetic energy of the particle at point B is smaller than the energy at point A .
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