Inductors And Ac:

Assume that you change the voltage source linked across a coil from dc to ac. Visualize that you can differ the frequency of the ac from a few hertz to hundreds of hertz, then kilohertz, and then finally megahertz.

Firstly, the ac will be high, just as is the situation with dc. Though, the coil has a certain amount of inductance, it takes a small time for current to establish itself in the coil. Based on how many turns there are and on whether the core is air or a ferromagnetic material, you will reach a point, as the ac frequency rises, whenever the coil begins to acquire sluggish. Which is, the current won't have time to get established in the coil before the polarity reverses? At high ac frequencies, the current via the coil has complexity following the voltage positioned across the coil. Just as the coil begins to "think" that it is making a good short circuit, the ac voltage wave pass its peak, goes back to zero, and then try to pull the electrons another way. This sluggishness in a coil for ac is, in effect, same to dc resistance. As the frequency is increased, the consequence gets more pronounced. Ultimately, when you keep on increasing the frequency of the ac source, the coil does not even come near establish a current with each cycle. It then acts like a large resistance. Barely any ac current flows via it.

The opposition which the coil offers to ac is termed as inductive reactance. It, such as resistance, is measured in ohms (?). It can vary just as resistance does, from near zero i.e., (a short piece of wire) to a few ohms (a small coil) to kilohms or megohms (bigger and bigger coils or coils with ferromagnetic cores at high frequencies). Inductive reactance can be represented on a ray, just like resistance, as shown in figure below.

Figure:  Inductive reactance can be symbolized on half-line or ray.  There is no limit to how large it can acquire, though it can never be negative.