SOLUTIONSUnitExam3A

SOLUTIONSUnitExam3A - ID A UCSD Physics 2B Answer Section...

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ID: A 1 UCSD Physics 2B Unit Exam 3 Current, Circuits, Power Answer Section MULTIPLE CHOICE 1. A R = V I 220 V 8.75 A = 25.1 Ω 2. B I = JA = nqv d Ê Ë Á Á ˆ ¯ ˜ ˜ A v d = I nqA = 1.1 × 10 4 A 41 × 10 12 m 3 Ê Ë Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ 1 × 1.60 × 10 19 C Ê Ë Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ 23 × 10 8 m 2 Ê Ë Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ = 7.3 × 10 7 m / s 3. C Since each parallel pair has resistance R/2, the total resistance of the circuit is 3R or 75 Ohms. By Ohm's Law, the current through the circuit is I = V R = 25 V 75 Ω = 0.333 A 4. B If you remembered that Q/L is charge density and speed is L/t, then I = Δ Q Δ t = Q L × L t = λ × v = 1.2 × 10 3 C / m Ê Ë Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ 26.7 m / s ( ) = 32.0 mA If you didn't, the only combination of the given quantities resulting in the correct units for current is the product. 5. C N = bulb 40 W Ê Ë Á Á Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ ˜ ˜ 7800 cents month Ê Ë Á Á Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ ˜ ˜ 1000 W hr 20 cents Ê Ë Á Á Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ ˜ ˜ day 24 hr Ê Ë Á Á Á Á Á Á
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