20_Chapter 21 HomeworkCH21 Alternating Current Circuits and Electromagnetic Waves

20_Chapter 21 HomeworkCH21 Alternating Current Circuits and Electromagnetic Waves

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220 CHAPTER 21 (b) For an ideal transformer, () () ( ) av av 2, rms 2, rms input ouput VI == PP () ( ) Thus, av 9.0 input P V 0.400 A 3.6 W 21.39 The power input to the transformer is ( ) 5 1, rms 1, rms 3 600 V 50 A 1.8 10 W input =∆ = = × P For an ideal transformer, ( ) av 2, rms 2, rms av ouput input = P P so the current in the long- distance power line is 5 av 2,rms 2, rms 1.8 1.8 A 100 000 V input I V × = P 2 22 1.8 A 100 3.2 lost line IR = × P The power dissipated as heat in the line is then The percentage of the power delivered by the generator that is lost in the line is 2 5 3.2 0% 100% 0.18% 1.8  × = ×=  ×  % Lost 10 lost input P P 21.40 (a) Since the transformer is to step the voltage down from 120 volts to 6.0 volts, the secondary must have fewer turns than the primary. (b) For an ideal transformer,
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