Question

What is the “time constant” for a capacitor, and why is it important?

Answer 1

We know that in a RC circuit the voltage in the capacitor when is charging is given by:

`V_C(t)=V_0(1-e^{-(t)/(RC)})`

when this is happening the voltage in the resistor is given by:

`V_R(t)=V_0e^{-(t)/(RC)}`

In both equations V0 denotes the voltage given by the source, R is the resistance of the resistor and C is the capacitance of the capacitor.

We notice that in both expressions the product RC appear, this product is what we call the time constant of the capacitor; and it is important since it determines the time intervals in which the voltage, charges and currents chage in a RC circuit. This means that while the capacitor is charging or discharging the variables mentioned will always have the time constant in their expressions.