Alternating Currents

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Alternating current (AC) is current whose magnitude changes continuously and direction changes periodically. In DC, current has constant magnitude and flows in only one direction. In India, AC has fre

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V = Vm cos ωt and I = Im cos ωt, where Vm and Im are peak values. RMS values: Vrms = Vm/√2 = 0.707 Vm and Irms = Im/√2 = 0.707 Im. RMS values represent the effective values - a DC current equal to Irm

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Given: R = 25 Ω, Vrms = 220V, f = 50 Hz Peak voltage: Vm = √2 × 220 = 311V Peak current: Im = Vm/R = 311/25 = 12.44A RMS current: Irms = Im/√2 = 220/25 = 8.8A Average power: P = I²rms × R = (8.8)² × 2

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In a purely resistive AC circuit, voltage and current are IN PHASE - they reach their maximum and minimum values at the same time. The phase difference φ = 0°. This is because resistance opposes curre

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Capacitive reactance (XC) is the opposition offered by a capacitor to AC current flow. XC = 1/(ωC) = 1/(2πfC). As frequency increases, XC decreases. At very high frequencies, XC → 0 (capacitor acts li

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In a purely capacitive circuit, current LEADS voltage by π/2 (90°). This is because current is proportional to rate of change of voltage: I = C(dV/dt). When voltage is at maximum (slope = 0), current

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Given: C = 100 × 10⁻⁶ F, Vrms = 220V, f = 50 Hz XC = 1/(2πfC) = 1/(2π × 50 × 100 × 10⁻⁶) = 1/(0.0314) = 31.8 Ω Irms = Vrms/XC = 220/31.8 = 6.92 A Note: As frequency increases, XC decreases and current

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Inductive reactance (XL) is the opposition offered by an inductor to AC current flow. XL = ωL = 2πfL. As frequency increases, XL increases. At very high frequencies, XL → ∞ (inductor blocks high frequ