The picture above shows an LRC circuit driven by a sinusoidal voltage source wit

Question

The picture above shows an LRC circuit driven by a sinusoidal voltage source with frequency f. The voltage and current are E and I, respectively, and the resonant frequency is fR. Choose true or false for each statement.
True False  If f > fR, then E leads I.
True False  If f=fR, then E lags I by exactly 90 degrees.
True False  If f=fR, then E and I are in phase.
True False  For any f, P=Erms*Irms.
True False  If f=fR, then E leads I by exactly 90 degrees.
True False  For fixed E, I is largest when f=fR.
True False  If f=fR, then P=Erms*Irms.

The picture above shows an LRC circuit driven by a sinusoidal voltage source with frequency f. The voltage and current are E and I, respectively, and the resonant frequency is fR. Choose true or false for each statement. True False If f > fR, then E leads I. True False If f=fR, then E lags I by exactly 90 degrees. True False If f=fR, then E and I are in phase. True False For any f, P=Erms*Irms. True False If f=fR, then E leads I by exactly 90 degrees. True False For fixed E, I is largest when f=fR. True False If f=fR, then P=Erms*Irms.

Explanation / Answer

If the frequency is too high, V_R leads V_AC. Since V_R and I are always in phase, this means that I leads V_AC.
So, the answer to the first question is false.

P_rms = E_rms*I_rms cos(f), where f is the phase angle.

At resonance, f=0, so P_rms=E_rms*I_rms.
So the answer to the 5th question is true.

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