Download TheWaterModel

The Water Model (Gravitational Analogy for Electrical Energy)
Three Cells in Series
Energy with Height Demonstration
One Series Cell Reversed
Three Cells in Parallel
One Parallel Cell Reversed
Every circuit can be looked at as if it has areas of high and
low energy. If you bend the circuit shown to the right and
then fold it as show below, it is easier to visualize.
The Water Model
Electrical charge can be viewed as being a little like water. It doesn’t leak out of the wires like
water can from a pipe, but there are other similarities.
…
The source can be viewed as a pump that “lifts” the charge to a higher energy, or it can be
viewed as someone lifting “Buckets of Charge” (called Coulombs) to the higher energy level
In this model “Voltage” is the height to which the charge is lifted.
Voltage is also sometimes viewed as water pressure. Very high “voltage” results in very high
pressure.
Energy with Height Demonstration (Back to Top)
This is a simple demonstration to make
that lasts forever once made.
Any rubber tubing can be used but
surgical tubing works best because
simply squeezing can stop the water
Raising the water filled bottle causes the bottom stream to
become faster and rise to a greater height.
A classroom sink is obviously an advantage although a
bucket can also be used to catch the water.
Three Cells in Series (Back to Top)
When the three cells compared to one, are correctly connected in series, the charge is lifted to
a much higher level. As it “falls” back it has more energy for the load to convert into other
forms. Series Activity [Link back to the Series Demo here] The following images are provided
for your use .
The above images are traditional schematic diagrams of the circuit pictures.
These images are meant to visually compare the Electrical Energy available from three cells
series to a one-cell circuit.
These images use the water model to visually compare the Electrical Energy available from
three cells series to a one-cell circuit.
One Series Cell Reversed (Back to Top)
Sometimes by accident, one cell is hooked in reverse. In this case the first two cells counteract
each other, leaving only the third to supply energy.
Three Cells in Parallel (Back to Top)
When the three cells compared to one, are correctly connected in parallel, the charge is not
lifted to a higher level. As it “falls” back it there is not any more energy for the load to convert.
What then is the advantage? Parallel Activity [Link back to the Series Demo here] The
following images are provided for your use .
The above images are traditional schematic diagrams of the circuit pictures.
These images are meant to visually show there is no more Electrical Energy (Voltage)
available from a three cell parallel circuit than from a one-cell circuit
These images are meant to suggest when cells are connected in parallel each cell does not
have to “work” as hard, hence will last longer. Note in the images below, the parallel “Buckets”
are smaller. The sources could alternatively provide more total current for a higher “wattage”
load.
One Parallel Cell Reversed (Back to Top)
Sometimes by accident, one cell is hooked in reverse. In
this case the two cells counteract the third, but the voltage
is left unchanged. The Parallel Activity [Link back to the
Series Demo here] can lead to confusion between voltage
and current
The diagram below is meant to show that the Voltage or
Energy Level remains unchanged but the middle source is “pumping” water (modelling
electrical current) in the wrong direction. Two sources against one.
It is a little like a short circuit. The current through the middle source will be very high. FOR
(non rechargeable alkaline) DRY CELLS THIS IS NOT DANGEROUS. It is difficult to explain
before students have an understanding of electrical Resistance. The Internal resistance of the
middle cell limits the current to a safe level. With time the cells will become hot, but it is unlikely
that they will be hot enough to cause damage. The cells will of course wear out more quickly.
The exact amount of current available to the load depends on the Internal resistance of the
backwards cell. This means the degree of brightness of the light bulb load will be hard to
predict or explain.