a) Ifenergy costs 16 cents perkilowatt-hour, how much does it cost to operate an

Question

a) Ifenergy costs 16 cents perkilowatt-hour, how much does it cost to operate an electric hairdryer for 2 minutes if theheating element has11.7 ohms ofresistance and is connected across 120 V?
b) Ifin the same building there are 10 60-Watt light bulbs on thestairwells and they operate 12 hours per day, how much does theowner have to pay for using them 30 days per month?
b) Ifin the same building there are 10 60-Watt light bulbs on thestairwells and they operate 12 hours per day, how much does theowner have to pay for using them 30 days per month?

Explanation / Answer

energy cost per 1 kW h = 16 cents time t= 2 min = 2/ 60 = 0.03333 h Resistance R = 11.7 ohm Voltage V = 120 V Power P ' = V ^ 2/ R = 1230.76 W energy E " = P ' t = 0.04102 kW h cost = E " * 16 cents         = 0.656 cents ( b) Total power used in 1 day is P = 10 * 60 = 600W energy utilised per day E = P * 12 h = 7200 W h = 7.2 kWh total energy used in 30 days per month E ' = 30 * E =216 kW h Owner pay = E ' * 16 cents= 3456 cents

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