**Some equations relating to capacitors:**
When a capacitor is discharged to produce an electric current, the decrease in the charge stored in the capacitor is exponential - it has a constant half-life. The equation for this discharge is:

x = x_{0} e^{-(t / CR)}

**t** is the time during which the capacitor discharges, **C** is the capacitance of the capacitor, and **R** is the resistance of the circuit connected to it. **x** can stand for the charge in the capacitor, **Q**, and it can also stand for the current and voltage of the resulting electric flow, **I** and **V**. Therefore as a capacitor discharges, **charge** in the capacitor and **current** and **voltage** in the circuit all decrease exponentially.

**C × R**, capacitance times resistance, is known as the **time constant** of a capacitor and is represented by **τ**, the letter tau. It is equal to the time, in seconds, taken by the values of **Q**, **I** and **V** (represented by **x** in the above equation) to decrease by a factor of **e**, the exponential function.

If capacitors are placed in parallel, the total capacitance is the sum of the individual capacitances:** C**_{total} = C_{1} + C_{2} + C_{3} etc. If they are placed in series, the total capacitance *decreases* according to the equation:** 1/C**_{total} = 1/C_{1} + 1/C_{2} + 1/C_{3} etc. Note that is the reverse of the case for resistors, which become less effective in parallel and more effective in series.

See also capacitor time constant