2009S2UnitExam5ASolutions

2009S2UnitExam5ASolutions - ID: A UCSD Physics 2B Answer...

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ID: A 3 UCSD Physics 2B Unit Exam 5A AC Circuits Answer Section MULTIPLE CHOICE 1. ANS: A Calculate and compare the AC reactance for each of the three load components: X R = R = 470 Ω X C = 1 ω C = 1 57.2 × 10 5 rad / s Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 320 × 12 F Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = 546 Ω X L = L = 57.2 × 5 rad / s Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 127 × 6 H Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = 726 Ω The resistor has the lowest reactance, and therefore (by Ohm’s Law) draws the most current. TOP: REACTANCE 2. ANS: C First find the current through the line given the power and voltage P = IV I = P V = 1.16 × 6 W 37.5 × 3 V = 30.93 A Then use Ohm's Law to calculate the voltage drop V = IR = A () 3.89 × 2 Ω Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = 1.20 V Beware of using P = V 2 R since the tranmission voltage is not the voltage drop across the leg. TOP: POWER TRANSMISSION LOSS 3. ANS: C Flux through a solenoid is the field times cross-section area times the number of turns: Φ= NBA = N μ 0 I N length Ê Ë Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ π R 2 Ê Ë
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2009S2UnitExam5ASolutions - ID: A UCSD Physics 2B Answer...

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