Impedance is mathematically symbolized by the letter “Z” and is measured in the unit of ohms (Ω), in complex form. When the alternating current goes through an impedance, a voltage drop is produced that is somewhere between 0° and 90° out of phase with the current.
It is present in all circuits, and in all components. This is a comprehensive expression of any and all forms of opposition to current flow, including both resistance and reactance. Reactance is mathematically symbolized by the letter “X” and is measured in the unit of ohms (Ω). When the alternating current goes through a pure reactance, a voltage drop is produced that is 90° out of phase with the current. It is present anywhere electric or magnetic fields are developed in proportion to an applied voltage or current, respectively but most notably in capacitors and inductors. This is essentially inertia against the flow of current. Resistance is mathematically symbolized by the letter “R” and is measured in the unit of ohms (Ω). When the alternating current goes through a resistance, a voltage drop is produced that is in-phase with the current. It is present in all conductors to some extent (except superconductors!), most notably in resistors. This is essentially friction against the flow of current. Before we begin to explore the effects of resistors, inductors, and capacitors connected together in the same AC circuits, let’s briefly review some basic terms and facts.
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