An AC circuit has a 10 Ω resistor and a 20 mH inductor connected in series to a 50 V (peak) source at 60 Hz. What is the impedance of the circuit?
Correct answer: C. 12.7 Ω
- A. 10.5 Ω
- B. 11.3 Ω
- C. 12.7 Ω
- D. 14.2 Ω
Explanation
Impedance Z = √(R² + X ), where XL = ωL, ω = 2πf = 2π × 60 ≈ 376.8 rad/s. XL = 376.8 × 0.02 = 7.536 Ω. Z = √(10² + 7.536²) = √(100 + 56.79) ≈ √156.79 ≈ 12.7 Ω.
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About Alternating Current
Alternating current varies periodically, so phase relationships become essential when current passes through a resistor, capacitor or inductor. The chapter distinguishes resistance from capacitive and inductive reactance, explains phase lead and lag, and connects changing electric and magnetic fields with the production and properties of electromagnetic waves.
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