776_Physics ProblemsTechnical Physics

776_Physics ProblemsTechnical Physics - 116*P27.40 Current...

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116 Current and Resistance *P27.40 The battery takes in energy by electric transmission P t V I t = = × F H G I K J = a f a f e j 2 3 13 5 10 4 2 3 600 469 3 . . . J C C s h s 1 h J. It puts out energy by electric transmission V I t a f a f e j = × F H G I K J = 1 6 18 10 2 4 3 600 249 3 . . J C C s h s 1 h J. (a) efficiency = = = useful output total input J 469 J 249 0 530 . (b) The only place for the missing energy to go is into internal energy: 469 249 221 J J J int int = + = E E (c) We imagine toasting the battery over a fire with 221 J of heat input: Q mc T T Q mc = = = ° = ° 221 15 1 J kg C 0.015 kg 975 J C . P27.41 P P 0 2 0 2 0 2 2 140 120 1 361 = = F H G I K J = F H G I K J = V R V R V V a f b g . % . . =
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