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# Reactive circuits watch

1. Hi i am doing some work on RC circuits (resistor & Capacitor) and i can analyse the circuit to get the impedance etc and draw a bode plot, but i am totally confused as to why the phase changes with frequency?! is it simply because the impedance of the capacitor changes with frequency, or is it something completely different?
any help would be great
thanks
Jamie
2. (Original post by pallister)
Hi i am doing some work on RC circuits (resistor & Capacitor) and i can analyse the circuit to get the impedance etc and draw a bode plot, but i am totally confused as to why the phase changes with frequency?! is it simply because the impedance of the capacitor changes with frequency, or is it something completely different?
any help would be great
thanks
Jamie
As far as I know, what you're saying is correct. Note that if you had a circuit with just a capacitor (no resistor), then the current would be out of phase referring to the voltage of the source. If you had no capacitor, just a resistor, then the current would be in phase with the voltage of the source. If there are both capacitance and resistance, the phase is somewhere in between - and the greater the capacitor's impedance is compared to the resistance (i.e. the smaller the frequency is), the greater its influence on the phase would be.
3. Thanks - that should help a lot, i have to design a multiband audio crossover using this

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