• summary_type: revision
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Pure resistor: I in phase with V. Impedance = R (frequency-independent). Power = V^2/R. Pure inductor: current lags voltage by pi/2 (ELI). Impedance = X_L = omegaL. Power = 0 (wattless). At DC: X_L = 0 (short circuit). At high f: X_L -> infinity (open). Pure capacitor: current leads voltage by pi/2 (ICE). Impedance = X_C = 1/(omegaC). Power = 0 (wattless). At DC: X_C -> infinity (open circuit). At high f: X_C -> 0 (short). These opposite frequency responses of L and C are the basis of resonance — at some frequency, their effects cancel perfectly. Phasor representation: V_R along I, V_L 90 degrees ahead of I, V_C 90 degrees behind I. The mnemonic ELI the ICE man captures all phase relationships. Energy storage: inductor stores LI^2/2 (magnetic), capacitor stores CV^2/2 (electric).