XL = 2* PI * F*L
A correct statement should be --- a coil of wire placed in series circuit allows MORE low frequency current but LESS high frequency current passing through.
I love some of the answers here. "It happens because of inductance", is basically the same as saying, "It happens because it happens".
These answers aren't really answers. I'll answer in plain English as best I can. It'll be wordy, and I may miss a few subatomic nuances, but I think I can get the basic idea across.
Let's start with DC. When you apply a DC voltage to a coil of wire, you'll see a magnetic field form around the coil. When you disconnect the power supply (cause the voltage to be zero) that magnetic field collapses. As you can imagine, it took time for the magnetic field to first form, and it also took time for the field to collapse. When a magnetic field collapses, the energy it took to form it in the first place gets turned back into current, which is to say, it moves electrons.
Now let's use AC. If you look at an AC sine wave, you'll notice the voltage builds to a maximum, and then falls to zero before building to a maximum again, this time of the opposite polarity. This is to say, it swings from positive to negative, and crosses zero between each one. Now, like I said before, it takes some time for the magnetic field to build up and collapse. If the frequency is relatively low, the magnetic field has plenty of time to build up and collapse right in line with the voltage. If the frequency of the applied voltage rises and falls at the exact same speed at which the magnetic field can build and collapse, the circuit is said to be in resonance. If the frequency of the applied voltage exceeds the rate as which the magnetic field can build up and collapse, you'll have one magnetic field in the process of collapsing while another one is trying to form.
The energy from the collapsing magnetic field is opposing that of the building magnetic field. The energy -wants- to go into building up the field, but since it's being opposed by the other collapsing field, the energy simply gets fed back into the circuit -in the opposite direction-.
SO, you have electrons moving in one direction trying to build up a magnetic field, but they're also being pushed in the opposite direction by the collapsing magnetic field. The net effect of all of this is measured as resistance. This effect only gets more pronounced as the frequency increases.
The coil has inductance and its impedance goes up with frequency. At DC it is 0.
a coil follows inductance principle it allows DC and blocks AC
thus when you pass low frequency it has low amplitude which is almost like DC thus it allows low frequency AC and pure DC
but high frequency is nothing but pure AC thus it gets blocked.
The coil has a resistance to change in voltage, but this resistance is lower at lower frequencies.
