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A resistance of 20 Ω, an inductance of 0.2 H and a capacitance of 100 μF are connected in series across 220-V, 50-Hz mains. Determine the following (a) impedance (b) current (c) voltage across R, L and C (d) power in watts and VA (e) p.f. and angle of lag |
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Answer» XC = 0.2 × 314 = 63Ω , C = 10μF = 100 × 10−6 = 10−4 farad XC = 1/ωC = 1/(314 x 10-4) = 32Ω, X = 63 − 32 = 31 Ω (inductive) (a) Z = √(202 + 31)2 = 37 Ω (b) I = 220/37 = 6 A (approx) (c) VR = I × R = 6 × 20 = 120 V; VL = 6 × 63 = 278 V, VC = 6 × 32 = 192 V (d) Power in VA = 6 × 220 = 1320 Power in watts = 6 × 220 × 0.54 = 713 W (e) p.f. = cos φ = R/Z = 20/37 = 0.54; φ = cos−1(0.54) = 57°18′ |
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