P213_Prelim_Ex_1_S08_Solns - Physics 213 1. 2. (a) F (b) F...

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Physics 213 Exam #1 Solutions Spring 2008 1. (a) F (b) F (c) F (d) T (e) F (f) F 2. 3. (a) C (b) C 4. (a) 3 = 2 < 1 (b) C B E 5. (a) ± (b) G [3 points for D or K] 6. (a) R = V / I = 1.5 V / 0.25 A = 6.0 ² (b) R = 0.5 V / 0.20 A = 2.5 ² ³ I = V / R = 1.5 V / 2.5 ² = 0.60 A (c) The resistance of a light bulb's filament increases as its temperature rises. 7. (a) -2Q [2 points] (b) Q encl = 2Q ´ µ · ¸ ¹ 4 3 ± r 3 4 3 ± a 3 = 2Q ´ µ · ¸ ¹ r 3 a 3 0 [1 point] º E = Q encl / » o ³ E(r) 4 ± r 2 = 2Q(r 3 /a 3 ) / » o +Q [2 points] ³ E(r) = Q r 2 ± » o a 3 = 2kQ r a 3 (c) 8. (a) I hd = 1800 W / 120 V = 15 A R lb = (120 V) 2 / 300 W = 48 ² R cp = (120 V) 2 / 600 W = 24 ² R lb + cp = 48 ² + 24 ² = 72 ² I lb + cp = 120 V / 72 ² = 1.67 A I total = 15 A + 1.67 A = 16.7 A (b)
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