Suppose that the cost of electrical energy is $0.094 per kilowatt hour (Dayton P

Question

Suppose that the cost of electrical energy is $0.094 per kilowatt hour (Dayton Power and Light, January 2013) and that your electric bill for 30 days is $70 (power usage only, not including other charges or taxes). Assume that the power delivered is constant over the entire 30 days. What is the power in watts? If a voltage of 110 V supplies this power, what current flows? Part of your electrical load is a 60-W light that is on continuously. By what percentage can your energy consumption be reduced by turning this light off?

Explanation / Answer

cost per unit is =$ 0.094 /kWhr

monthly bill is =$ 70

so total units consumed per month is = 70 / 0.094 =744.68kWhr

Asuming constant load

power demand of load is =744.68 / 24/30=1.0343kW =1034.3W

if the voltage supply is 110V

so current will be =1034.3/110= 9.403A

If you turn off 60W bulb the power demand will be = 1034.3-60= 974.3W

total unit per month=974.3*24*30/1000=701.5kWhr

so energy saving will be =744.68-701.5= 43.2 kWhr

energy saving in percentage will be=43.2/744.68*100 = 5.8%

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