Question

7. A TV draws a current of 1.75 A when connected to a 120 V household circuit. a) What is the resistance of the TV? b) What is the power dissipated by the TV? c) At $0.0858 per kWh, how much money will it cost to run the TV for 4 hours? d) If the resistance of the TV is doubled, how much power will it dissipate now? Does your answer make sense?

Answer 1

Let resistance of TV is R Partial Since we know that By ohm�s Law V = IR = > I = v/R therefore R = V/I = 120/1.75 R = 68.57 Ohm Power dissipated by the TV P = i^2 R = v^2/R P = (120)^2/68.57 = 210.004 waH therefore p = 210 waH or P = 210 J/s. Since we know that energy (in kwh) = power (in kw) times time (in hstrok). \r\n = power (in watt) times time (in hour)/1000 therefore Energy (in kwh) = 210 times 4/1000 = 0.84 kwh cost of electricity = electrical energy in kwh times cost per kwh = 0.84 times 0.0858 $ = 0.072072 $ if R prime = 2R if R prime = 2R therefore P prime = v^2/R prime = v^2/2R p prime = 1/2 (v^2/R) = P/2 p prime = P/2 = 210/2 = 105 Wa H Therefore on doubling the value of resistance the new