Capacitors, Diodes, Etc.

Capacitors store electrical charge. This charge is built up along one of the capacitors two plates, and is released when there is a short between the plates. Capacitance is measured in farads. One farad is an enormous quantity of charge. Most capactitors are much smaller, in the micro and picofarad range.

A capacitor can be charged almost instantly if it's leads are connected directly to a power supply. It is possible to increase the charging time by adding a resistor between the power supply and the capacitor. The actually formula for determining the charging time is q=q_initial[1-e^-t/(RC)]. RC is a time constant equal to the time required for the capacitor to accumulate 63.2% of its equilibrium charge. In addition to releasing it's charge by shorting, a capacitor may also lose it's charge by "leaking" after it is completely charged. This process can be slowed by connectioning a resistor across the two leads of the capacitor. The larger the resistor, the longer the discharge will take. The formula for discharging is q=q_initiale^-t/(RC) .

Finding total capacitance is the opposite of finding total resistance, in that when determining the total amount of capacitance in series, you use 1 over the sum of the reciprocals of the capacitors. This gives you C_total.When finding the total capacitance in parallel, you just have to add the the values of the capacitors together.

Diodes only allow the flow of current in one direction.