Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 17)

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Capacitors: Capacitors are electrical components that
can store electrical pressure (voltage) for periods of time.
When a capacitor has a difference in voltage (electrical
pressure) across it, it is said to be charged. A capacitor
is charged by having a one-way current flow through it for
a short period of time. It can be discharged by letting a
current flow in the opposite direction out of the capacitor.
In the water pipe analogy, you may think of the capacitor
as a water pipe that has a strong rubber diaphragm
sealing off each side of the pipe as shown below:
If the pipe had a plunger on one end (or a pump
elsewhere in the piping circuit), as shown above, and the
plunger was pushed toward the diaphragm, the water in
the pipe would force the rubber to stretch out until the
force of the rubber pushing back on the water was equal
to the force of the plunger. You could say the pipe is
charged and ready to push the plunger back. In fact if the
plunger is released it will move back to its original
position. The pipe will then be discharged or with no
pressure on the diaphragm.
Capacitors act the same as the pipe just described.
When a voltage (electrical pressure) is placed on one
side with respect to the other, electrical charge “piles up”
on one side of the capacitor (on the capacitor “plates”)
until the voltage pushing back equals the voltage applied.
The capacitor is then charged to that voltage. If the
charging voltage was then decreased the capacitor
would discharge. If both sides of the capacitor were
connected together with a wire then the capacitor would
rapidly discharge and the voltage across it would become
zero (no charge).
What would happen if the plunger in the drawing above
was wiggled in and out many times each second? The
water in the pipe would be pushed by the diaphragm and
then sucked back by the diaphragm. Since the
movement of the water (current) is back and forth
(alternating) it is called an alternating current or AC.
The capacitor will therefore pass an alternating current
with little resistance. When the push on the plunger was
only toward the diaphragm, the water on the other side of
the diaphragm moved just enough to charge the pipe (a
transient or temporary current). Just as the pipe blocked
a direct push, a capacitor blocks a direct current (DC).
Current from a battery is an example of direct current. An
example of alternating current is the 60 cycle (60 wiggles
per second) current from the electrical outlets in the walls
of your house.
Construction of Capacitors: If the rubber diaphragm is
made very soft it will stretch out and hold a lot of water
but will break easily (large capacitance but low working
voltage). If the rubber is made very stiff it will not stretch
far but will be able to withstand higher pressure (low
capacitance but high working voltage). By making the
pipe larger and keeping the rubber stiff we can achieve a
device that holds a lot of water and withstands high
pressure (high capacitance, high working voltage, large
size). So the pipe size is determined by its capacity to
hold water and the amount of pressure it can handle.
These three types of water pipes are shown below:
INTRODUCTION TO CAPACITORS
Pipe Filled with Water
Rubber Diaphragm
Sealing Center of Pipe
Plunger
A Rubber Diaphragm in a Pipe is Like a Capacitor
Soft Rubber
Types of Water Pipes
Stiff Rubber
Stiff Rubber
Large Capacity
Low Pressure
Low Capacity
but can withstand
High Pressure
High Capacity and can withstand High Pressure