A transformer supplies 10 kW at 96% efficiency. At this load its copper loss is 250 W. Core loss is constant. If the load current is halved at the same power factor and approximately constant secondary voltage, what is the new efficiency closest to?
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Question

A transformer supplies 10 kW at 96% efficiency. At this load its copper loss is 250 W. Core loss is constant. If the load current is halved at the same power factor and approximately constant secondary voltage, what is the new efficiency closest to?

Options

G1 Physics · Accepted Answer

Initial input=10000/0.96=10416.67 W, so total loss=416.67 W and core loss=166.67 W. At half current, output≈5000 W and copper loss=250/4=62.5 W. η=5000/(5000+166.67+62.5)=0.9562≈95.6%. Closest option is 95.2%.