A 120 V (rms) power line is connected to the primary of a step-down transformer, with a turn ratio of 12: 1. The transformer's secondary is connected to a doorbell, which requires 9.330 W of electric power for its operation. What is the peak instantaneous current in the primary?
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The secondary current is Is=9.33/10=.933 amps. If you neglect the magnetizing current, the primary current will be Is/12=.0777 amps. The peak value will be sqrt(2)*.0777.