In an AC circuit the total opposition to the flow of current is termed

• A. Admittance
• B. Impedance
• C. Resistance
• D. Reactance

Answer: (B)

In AC circuits the total opposition to current is called impedance. This isn’t just resistance; it combines resistance and reactance into a single quantity that has both magnitude and phase. Impedance is written as Z = R + jX, where R is the resistance and X is the net reactance (the difference between inductive and capacitive reactance). The magnitude of the opposition is |Z| = sqrt(R^2 + X^2), and the phase angle φ = arctan(X/R) tells you how much the current lags or leads the voltage. Inductive reactance makes current lag, while capacitive reactance makes it lead; the total opposition reflects both effects. Reactance alone is only the imaginary part and doesn’t capture the full opposition, and admittance is the reciprocal of impedance, describing how easily current can flow.