2

Passive circuits

Resistors, capacitors and inductors can be combined for various purposes. When a circuit contains both resistance and reactance, it presents an ‘impedance’ Z which varies with frequency. Thus Z = R +L (resistor in series with an inductor) or Z = R - j/(ωC) (resistor in series with a capacitor). The reciprocal of impedance, Y, is known as admittance, so I = E/Z and E = I/Y

At a given frequency, a resistance and a reactance in series Rs and Xs behaves exactly like a different resistance and reactance in parallel Rp and Xp. Occasionally, it may be necessary to calculate the values of Rs and Xs given Rp and Xp, or vice versa. The necessary formulae are given in Appendix 1.

Since the reactance of an inductor rises with increasing ...

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