21_Chapter 17 HomeworkCH17 Current and Resistance

21_Chapter 17 HomeworkCH17 Current and Resistance - Current...

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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 Et =⋅ = = × = 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 VR =∆ P , the total resistance needed is 22 20 V
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