In AC circuits, Ohm's law uses impedance Z: V = I × Z. Which statement is true?

In AC circuits, Ohm's law uses impedance Z: V = I × Z. Which statement is true?

• A. V = I × Z
• B. V = I × R
• C. V = Z / I
• D. V = R × Z

Answer: (A)

In AC circuits, Ohm's law uses impedance to relate voltage and current because impedance captures both the resistive part and the reactive part that comes from capacitors and inductors. Impedance is a complex quantity Z = R + jX, where R is resistance and X is reactance. The voltage and current in AC are phasors, so the relationship is V = I × Z. This means the voltage and current have a magnitude relation |V| = |I| × |Z| and a phase difference equal to the angle of Z. When there is only a resistor (no reactance), Z reduces to R and you recover V = I × R. The other forms don’t hold in general: V = I × R only applies for purely resistive circuits; V = Z / I would invert the relationship and misrepresent units; V = R × Z would mix two impedances and isn’t a correct expression for voltage.

In AC circuits, Ohm's law uses impedance to relate voltage and current because impedance captures both the resistive part and the reactive part that comes from capacitors and inductors. Impedance is a complex quantity Z = R + jX, where R is resistance and X is reactance. The voltage and current in AC are phasors, so the relationship is V = I × Z. This means the voltage and current have a magnitude relation |V| = |I| × |Z| and a phase difference equal to the angle of Z. When there is only a resistor (no reactance), Z reduces to R and you recover V = I × R. The other forms don’t hold in general: V = I × R only applies for purely resistive circuits; V = Z / I would invert the relationship and misrepresent units; V = R × Z would mix two impedances and isn’t a correct expression for voltage.