文档介绍：Reading 11 Ron Bertrand VK2DQ
CAPACITANCE
In this reading we are going to talk about capacitance. I have to make a distinction here
between capacitor and capacitance. A capacitor is a device, whereas capacitance is an
electrical property. First we will discuss the capacitor and then the property of capacitance.
We will avoid mathematics where possible.
Construction
Figure 1(a).
Figure 1(b).
As you can see a capacitor is a two terminal device. There is always an insulator between
the plates of a capacitor. This should suggest to you that current never flows through a
capacitor.
Page 1
Some basic schematic symbols for capacitors:
Figure 2.
Figure 2(b) shows a polarised (electrolytic) capacitor. This type of capacitor has its
dielectric formed electrically, and must only be used in DC circuits. Figures 2(c), (d), and
(e) are all variable capacitors. Figure 2(d) is often called a trimmer capacitor, as it is
adjusted with a small screwdriver and is often used to “trim” the capacitance in a circuit.
Sometimes two or more variable capacitors are used on the one shaft, so that when the
shaft is turned, all of the capacitors are made to vary. This is shown in 2(e). With such a
capacitor,