808_Physics ProblemsTechnical Physics

808_Physics - 148 P28.49 Direct Current Circuits(a P = IV 1 500 W P = = 12.5 A V 120 V 750 W I= = 6.25 A 120 V I= So for the Heater For the Toaster

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148 Direct Current Circuits P28.49 (a) P = IV : So for the Heater, I V == = 1500 12 5 W 120 V A .. For the Toaster, I 750 625 W 120 V A And for the Grill, I 1000 833 W 120 V A (b) 12 5 6 25 8 33 27 1 . . ++= A The current draw is greater than 25.0 amps, so this circuit breaker would not be sufficient. P28.50 IR I R Al 2 Al Cu 2 Cu = so I R R II Al Cu Al Cu Cu Al Cu A === = = ρ 170 282 20 0 0 776 20 0 15 5 . . . . a f a f P28.51 (a) Suppose that the insulation between either of your fingers and the conductor adjacent is a chunk of rubber with contact area 4 mm 2 and thickness 1 mm. Its resistance is R A =≈ × ≈× A 10 10 41 0 21 0 13 3 6 15 m m m 2 ej e j . The current will be driven by 120 V through total resistance (series) 0 1 0 0 51 0 15 4 15 15 × + ΩΩ . It is: I V R = × ~~ 120 10 14 V 0 A 15 . (b) The resistors form a voltage divider, with the center of your hand at potential V h 2 , where V h is the potential of the “hot” wire. The potential difference between your finger and thumb is ∆Ω VI R = −− 10 10 10 14 4 10 A V e j . So the points where the rubber meets your fingers are
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .

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