One particular plug-in power supply for a radio looks similar to the one shown i
ID: 1375517 • Letter: O
Question
One particular plug-in power supply for a radio looks similar to the one shown in the figure below and is marked with the following information: Input 120 VAC 10 W Output 6 V DC 280 mA. Assume these values are accurate to two digits The primary winding in this transformer is attached to the p of the plug, whereas the secondary winding is connected to the power cord on the right. (a) Find the energy efficiency of the device when the radio is operating. (b) At what rate is energy wasted in the device when the radio is operating? (c) Suppose the input power to the transformer is 10.00 W when the radio is switched off and energy costs $0.105/kWh from the electric company. Find the cost of having seven such transformers around the house, each plugged in for 31 daysExplanation / Answer
a)
efficiency = output Power *100/input power
efficiency = 6 *0.280 *100/10
efficiency = 16.8 %
b_
Power wasted = (1 - 0.168) * 10
Power wasted = 8.32 W
c)
Now, cost of operation = energy * 0.105
cost of operation = 7 * 24 * 31 * 0.00832 * 0.105
cost of operation = 4.55 $
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