While a resistor is a
component that resists the flow of charge through it, a capacitor
stores charge. Capacitance is measured in
(or more formally,
Faradays) with an equation
symbol C and a unit symbol F. Typical capacitors you will use will
range in value from μF (microFarads) down to pF (picoFarads).
The relationship between current, capacitance, and voltage is given by:
I = C * dV/dt
where dV/dt is the rate of voltage change over time.
The schematic symbols for capacitors are shown in Figure 2-10. The component on the left is
bipolar, while the other two are
unipolar. A unipolar capacitor has a positive lead and a
negative lead, and it must be inserted into a circuit with the
correct orientation. Failing to do so will cause it to explode.
(Unipolar capacitors have markings to indicate their orientation.) A
bipolar capacitor has no polarity.
Figure 2-10. Capacitor symbols
Applying a voltage across a capacitor causes the capacitor to become charged. If the voltage source is removed and a path for current flow exists elsewhere in the circuit, the capacitor will discharge and thereby provide a (temporary) voltage and current source (Figure 2-11).
Figure 2-11. Capacitor charging and discharging
This is an extremely useful characteristic. A given voltage source may have a ...