High Frequencies
4. AC Circuits and Impedance
Ohm's Law, in its simplest form, applies primarily to direct current (DC) circuits with purely resistive loads. When you start dealing with alternating current (AC) and components like inductors and capacitors, things get a bit more complicated. These components introduce something called impedance, which is the AC equivalent of resistance.
Inductors and capacitors store energy in electric and magnetic fields, respectively. This means they resist changes in current and voltage. In an AC circuit, the current and voltage are constantly changing, so inductors and capacitors are constantly charging and discharging, creating a complex relationship between voltage and current that is not simply proportional as Ohm's Law suggests. In these circuits, we often use a concept called impedance (Z), which takes into account resistance (R) as well as inductive reactance (XL) and capacitive reactance (XC). Impedance is measured in Ohms, but the relationship between voltage, current, and impedance is described by V = IZ, which is a more general form of Ohm's Law that accounts for the phase differences between voltage and current in AC circuits.
Furthermore, at very high frequencies, the wiring and even the components themselves can start to behave like inductors and capacitors, further complicating the analysis. This is why high-frequency circuit design requires specialized techniques and tools.
So, in AC circuits, especially at higher frequencies, Ohm's Law is still relevant but needs to be applied with a bit more sophistication. You need to consider impedance rather than just resistance, and you might need to use more advanced circuit analysis techniques to accurately predict circuit behavior. Ohm's law then becomes a special case of a more general theory. It's a solid building block, but not the whole structure.
