The correct answer is: A. Low
A parallel R-L circuit behaves as purely resistive at low frequencies. This is because the inductive reactance of the inductor is very small at low frequencies, and can be neglected. The impedance of the circuit is therefore equal to the resistance of the resistor, and the current through the circuit is in phase with the voltage across the circuit.
At high frequencies, the inductive reactance of the inductor becomes large, and the impedance of the circuit is dominated by the reactance. The current through the circuit is therefore out of phase with the voltage across the circuit.
The following is a brief explanation of each option:
- Option A: Low frequencies
At low frequencies, the inductive reactance of the inductor is very small, and can be neglected. The impedance of the circuit is therefore equal to the resistance of the resistor, and the current through the circuit is in phase with the voltage across the circuit.
- Option B: Very low frequencies
At very low frequencies, the inductive reactance of the inductor is even smaller than at low frequencies, and can be neglected even more. The impedance of the circuit is therefore even closer to the resistance of the resistor, and the current through the circuit is even closer to being in phase with the voltage across the circuit.
- Option C: High frequencies
At high frequencies, the inductive reactance of the inductor becomes large, and the impedance of the circuit is dominated by the reactance. The current through the circuit is therefore out of phase with the voltage across the circuit.
- Option D: Very high frequencies
At very high frequencies, the inductive reactance of the inductor is even larger than at high frequencies, and the impedance of the circuit is even more dominated by the reactance. The current through the circuit is therefore even further out of phase with the voltage across the circuit.