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Capacitors
In our experiments in this chapter, we’re going to use electrolytic
capacitors, not because we like to be awkward, but
because the values of capacitance we want are quite high. And
electrolytic capacitors are generally the only ones capable of
having these values, while keeping to a reasonable size and
without being too expensive. Anyway, not to worry, all you
have to do is remember to put the capacitors into circuit the
right way round.
You can make sure of this, as all electrolytic capacitors have
some kind of marking on them which identifies positive and
negative plates. Figure 4.3 shows two types of fairly typical
electrolytic capacitors. One, on the left, has what is called an
axial body, where the connecting leads come out from each
end. One end, the positive plate end, generally has a ridge
around it and sometimes is marked with positive symbols (as
mine is). Sometimes, the negative plate end has a black band
around it, or negative symbols.
The capacitor on the right has a radial body, where both leads
come out from one end. Again, however, one or sometimes
both of the leads will be identified by polarity markings on
the body.
Whatever type of electrolytic capacitor we actually use in
circuits, we shall show the capacitor in a breadboard layout
diagram as an axial type. This is purely to make it obvious
(due to the ridged positive plate end) which lead is which.
Both types are, in fact, interchangeable as long as the correct
polarity is observed, and voltage rating (that is, the maximum
voltage which can be safely applied across its leads — usually
written on an electrolytic capacitor’s body) isn’t exceeded.
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