Resistorcapacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors driven by a voltage or current source. The 1st order RC circuit composed of one resistor and one capacitor, is the simplest example of an RC circuit.RC circuits, like other types of circuits, are used to 'filter' a signal waveform, changing the relative amounts of low-frequency and high-frequency information in their output signals relative to their input signals. There are high-pass filter and low-pass filter and band-pass filter versions. A common application is for smoothing a signal, using a low-pass version.
During the charging of a capacitor, the current in the RC circuit
is given by
I ( t ) = (V/R)*exp( -t / T)
where V is the battery emf, R is the resistance, and T = RC is
called the RC circuit time constant. On the other hand, the charge on the capacitor varies with time according
Q ( t ) = CV [1 exp( -t / T)]
When a capacitor discharges through a resistance R, the charge on
the capacitor decreases with time according to Q ( t ) = Q_initial *exp ( -t / T)
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