One particular plug-in power supply for a radio looks
Chapter 33, Problem 55(choose chapter or problem)
One particular plug-in power supply for a radio looks similar to the one shown in Figure 33.20 and is marked with the following information: Input 120 V AC 8 W Output 9 V DC 300 mA. Assume these values are accurate to two digits. (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 8.00 W when the radio is switched off and energy costs $0.110/kWh from the electric company. Find the cost of having six such transformers around the house, each plugged in for 31 days.
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