Problem 4.136

A solenoid with inductance \(L=7 \mathrm{mH}\) and active resistance \(R=44 \Omega\) is first connected to a source of direct voltage \(V_{0}\) and then to a source of sinusoidal voltage with effective value \(V=V_{0} .\) At what frequency of the oscillator will the power consumed by the solenoid be \(\eta=5.0\) times less than in the former case?