A wire of resistance R is wound into a coil of inductance L. What is the impedance of the coil at frequency f?
Correct answer D. √(R² + 4π²f²L²)
Explanation
Resistance and inductive reactance 2πfL are 90° out of phase, so they combine like perpendicular vectors: Z = √(R² + 4π²f²L²).
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