798_Physics ProblemsTechnical Physics

798_Physics ProblemsTechnical Physics - 138 Direct Current...

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138 Direct Current Circuits P28.18 (a) V IR = : 33 0 11 0 1 . . V = I a f 33 0 22 0 2 . . V = I a f I 3 3 00 = . A I 2 1 50 = . A P = I R 2 : P 1 2 3 00 11 0 = . . A a f a f P 2 2 1 50 22 0 = . . A a f a f P 1 99 0 = . W P 2 49 5 = . W The 11.0- resistor uses more power. (b) P P 1 2 148 + = W P = = = I V a f a fa f 4 50 33 0 148 . . W FIG. P28.18(a) (c) R R R s = + = + = 1 2 11 0 22 0 33 0 . . . V IR = : 33 0 33 0 . . V = I a f , so I = 1 00 . A P = I R 2 : P 1 2 1 00 11 0 = . . A a f a f P 2 2 1 00 22 0 = . . A a f a f P 1 11 0 = . W P 2 22 0 = . W The 22.0- resistor uses more power. FIG. P28.18(c) (d) P P 1 2 2 1 2 2 1 00 33 0 33 0 + = + = = I R R b g a f a f . . . A W P = = = I V a f a fa f 1 00 33 0 33 0 . . . A V W (e) The parallel configuration uses more power. *P28.19 (a) The resistors 2, 3, and 4 can be combined to a single 2 R resistor. This is in series with resistor 1, with resistance R , so the equivalent resistance of the whole circuit is 3 R . In series, potential difference is shared in proportion to the resistance, so resistor 1 gets 1 3 of the battery voltage and the 2-3-4 parallel combination get 2 3 of the battery voltage. This is the potential difference across resistor 4, but resistors 2 and 3 must share this voltage. 1 3 goes to 2 and 2 3 to 3. The ranking by potential difference is
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