Starting Out in Electronics (7): Easier Than Imagined!Even When It Is About Capacitors

摘要

A capacitor can be considered to be two conductors (metal plates, for example, or more generally, electrodes) that are placed a very short distance from each other, but do not actually make electrical contact with each other. This concept is also expressed in the schematic symbol (Figure 1): two parallel lines that are not connected together.But hang on! How is it possible that a component does not allow DC signals to pass but does allow AC signals to pass? We can make this clear when we consider what 'current' really is: the transport of charge. When charge is transported, a current flows. When we connect a capacitor to a DC voltage, there will be an initial current - electrons move from one plate of the capacitor to the positive terminal of the DC voltage source, and from the negative terminal, electrons move to the other plate. But once the capacitor has been charged in this way, the electrons have nowhere else to go any more - they cannot move magically from one plate to the other. There is no longer any current flow, and the capacitor behaves as an open circuit (or isolator, or resistor with an infinitely high value).connected to the capacitor: the capacitor is then continuously charged, discharged, charged in the opposite polarity, etc, - and then a current most certainly flows back and forth (an AC current, that is). And, to be absolutely clear, no electrons actually move through the capacitor from one plate or electrode to the other!