A 120V AC circuit with a 4 Ω impedance has what current?

A 120V AC circuit with a 4 Ω impedance has what current?

• A. 30 A
• B. 0.033 A
• C. 120 A
• D. 4 A

Answer: (A)

Current in an AC circuit follows Ohm’s law using impedance: I = V / Z, using the magnitudes. With a 120 V supply and a 4 Ω impedance, the current magnitude is 120 / 4 = 30 A. Since the impedance is purely resistive, the current is in phase with the voltage. If you were using peak values instead of RMS, the peak current would be 120√2 / 4 ≈ 42.4 A, but in standard calculations we use RMS, so the current is 30 A.

Current in an AC circuit follows Ohm’s law using impedance: I = V / Z, using the magnitudes. With a 120 V supply and a 4 Ω impedance, the current magnitude is 120 / 4 = 30 A. Since the impedance is purely resistive, the current is in phase with the voltage. If you were using peak values instead of RMS, the peak current would be 120√2 / 4 ≈ 42.4 A, but in standard calculations we use RMS, so the current is 30 A.