I know the mathematics and equations behind the circuitry and how they tell us that the resistor blocks high frequency ac signals and allows low frequency ac signals to pass through with undiminished amplitude. Similarly, a capacitor blocks low frequency ac signals and allows high frequency ac signals to pass through with undiminished amplitude.

But what is the physics behind this? Can anyone explain to me this phenomenon without using any mathematics?

I did not find a proper theoretical explanation for this anywhere.

  • 1
    $\begingroup$ It is unclear what you want. You said you know the math and circuitry behind it, so the only thing left is to understand the physics behind how the components themselves operate, which is a Wikipedia page away... $\endgroup$
    – JamalS
    Apr 25, 2017 at 16:49
  • $\begingroup$ The mathematical derivation for it should be entirely based on the circuit, which is physics. If you understand how to get it with the math, just consider what you are actually doing. $\endgroup$
    – JMac
    Apr 25, 2017 at 16:51
  • $\begingroup$ The resistor isn't blocking anything. $\endgroup$
    – Jon Custer
    Apr 25, 2017 at 17:06
  • $\begingroup$ @JonCuster, unless it has some parasitic inductance. $\endgroup$
    – The Photon
    Apr 25, 2017 at 17:16
  • 1
    $\begingroup$ @ThePhoton - having used a precision wire-round resistor as a 'precision' small value inductor before, I can agree to some extent... $\endgroup$
    – Jon Custer
    Apr 25, 2017 at 17:36

1 Answer 1


In a low pass circuit, the capacitor can absorb small amounts of charge without the voltage changing much. When you put a high frequency signal into the low pass filter, the capacitor acts as a short circuit - the small amount of charge that flows in one half cycle can be "absorbed" by the capacitor without the voltage changing significantly. When the frequency is lower, the capacitor has time to charge and the voltage changes - so the circuit "let's through" the input signal.

You can do a similar analysis for the high pass configuration - again ask yourself how the voltage across the capacitor changes with time.


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