If electrical energy costs 12 cents, or $0.12, per kilowatt-hour, then what woul

Question

If electrical energy costs 12 cents, or $0.12, per kilowatt-hour, then what would the following events cost? (a) burning a 120 W light bulb for 24 h straight (b) operating an electric oven for 4.0 h if it carries a current of 20.0 A at 220 V The potential difference across a resting neuron in the human body is about 65.0 mV and carries a current of about 0.300 mA. How much power does the neuron release? The cost of electricity varies widely throughout the United States; $0.120/kWh is a typical value. At this unit price, calculate the cost that would result from each of the following: (a) leaving a 60.0 W porch light on for 2 weeks while you are on vacation $ (b) Making a piece of dark toast in 3.00 min with a 850 W toaster. $ (c) drying a load of clothes in 40.0 min in a 4900 W dryer $

Explanation / Answer

Energy = 120*24 = 2880 Wh = 2.88 kwh
so
cost = 2.88*$0.12 = $0.3456
b)
Energy =powerxtime = VI *t = 20*220*4 = 17600 Wh = 17.6 Kwh
cost
17.6*$0.12 =$2.112
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10.
a)
power = VI = 65x10^-3*0.3x10^-3 = 19.5 uW
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11.
a)
2 weeks = 2*7 days = 14 days = 14*24 = 336 hours
Energy consumed = 60*336 = 20.160 Kwh
cost = 20.160*$0.12 = $2.4192
b)
3 min = 3/60 hours = 0.05 hours
energy = 850*0.05 = 42.5 w h= 0.0425 Kwh
cost = 0.0425*$0.12 = $0.0051
c)
40 min = 40/60 hours = 0.667 hours
energy = 4900*0.667 = 3266 wh = 3.266 Kwh
cost = 3.266*$0.12 = $0.391

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