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Can someone clearly explain what it is meant by the time constant of an RC circuit. Because from what I have been told it is the time taken to charge the capacitor. However, when I search on google it mentions that it is the time taken to charge approx. 63% of the initial voltage. What if the initial voltage is 0V?

Would this definition apply to RL and RLc circuits as well?

I have probably missed something trivial.

Any help would be much appreciated. Thanks!

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Remember the charging equation:

$$V(t) = V_0(1-e^{-t/\tau})$$

When $t=\tau$, $V(\tau)=V_0(1-\frac{1}{e}) = 0.63V_0$

So the time constant, $\tau$, in this case is the time in which the voltage, $V(t)$, equals 63% of the supply voltage, $V_0$. For an RC circuit, $\tau=RC$.

The other circuits have time constants that mean similar things.

If you are charging something, your initial voltage in the thing you are charging is zero. You may be confusing this 'initial' part with discharging a capacitor.

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