21_Ch 17 College Physics ProblemCH17 Current and Resistance

21_Ch 17 College Physics ProblemCH17 Current and Resistance...

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Current and Resistance 89 (c) The time for the dim bulb to dissipate 1.00 J of energy is 1.00 J 0.040 0 s 25.0 W dim E t ∆ = = = P Electrical potential energy is transformed into internal energy and light (d) In 30.0 days, the energy used by the dim bulb is ( )( ) ( ) 4 25.0 W 30.0 d 24.0 h d 1.80 10 Wh 18.0 kWh dim E t = ⋅ = = × = P ( ) and the cost is ( ) 18.0 kWh $0.070 0 kWh $1.26 t E rate = = = cos The electric company sells energy , and the unit cost is 8 6 $0.070 0 1 kWh $1.94 10 Joule kWh 3.60 10 J unit cost = = × ×  17.49 From ( ) 2 V R = ∆ ( ) P , the total resistance needed is (
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