Inductors

[windozeuser]

How do inductors really work? I know the textbook definition of storing energy in it's magnetic field. That isn't good enough for me.

Plus how can they reject a range of frequencies such as in a radio to tune all but one station.

 

[_3iMaJ]

If you understand the physics of it then you basically understand the filtering capabilities.

Here is how:

If you take an RL circuit for example. Write the KVL and get the differental equation. Either use Laplace or Fourier to solve your differential equation (for voutput/vsource). Once you have this you've seen how they reject some frequencies and pass others. It is all brought together by the v = L*di/dt and the connection to the frequency domain courtesy of Fourier

 

[ljcox]

An inductor alone cannot tune to a particular frequency. You need both an inductor and a capacitor. Capacitors store energy in the electric field between their plates.

As your first respondant said, the voltage across an inductor is given by V = L* di/dt where di/dt is the rate of change of the current through the inductor. For a capacitor, it is i = C* dV/dt where dV/dt is the rate of change of the voltage across the capacitor.

If you do the maths, you will find that a parallal LC circuit will resonate at f = 1/ {2*Pi*sqrt(L*C)} where f is the frequency at resonance. At reasonance, the voltage across the circuit is a maximum and this is why it passes that particular frequency and not others.

For a series LC circuit, the current will rise to a maximum at resonance.

Len

 

[ThermalRunaway]

Laplace and fourier transforms, yuckkkk. Please don't sware at me

I hated that kind of maths when I was studying Electronics Engineering. I just about managed enough understanding of it to carry me through, but it's definately not easy going.

Brian

 

[checkmate]

Laplace and Fourier Transforms are a godsend. Or would you rather prefer O.D.E? :lol: