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Voltage:
As we said on the previous page, if work is to be done, something has to move. For something to move, a force has to be applied to the object. In electronics, that force is voltage. Voltage is the measure of difference of potential (electrical force) between two points. The volt is
the unit of measure. Voltage can be described as electrical pressure.
Water Analogy:
If you look at the two water towers below, you can see that one is taller than the other. You can also see the water level is higher (with respect to the outlet of the faucet). This means that the column of water is taller and therefore applies more pressure on the bottom of the column of water (this is the pressure you feel on your ears when you swim to the bottom of a deep swimming pool). Since the taller column of water is exerting more pressure on the bottom of the water column, the pressure will be greater at its faucet (because of the greater difference between the top of the water in the tower and the level of the faucet). The taller tower would force more water from the faucet in a given amount of time than the short tower. The difference of 'potential' is relative to the height of the column of water above the faucet. If the faucet was at the same level as the top of the water column, there would be virtually no water flow because there would be no difference of potential.
In the following diagram you can see that there are now 2 faucets on the taller tower. You can also see that the vertical distance from the top of the water column (on the taller tower) to the outlet of the higher faucet is the same as the distance from the top of the water column on the smaller tower to its faucet's outlet. The higher faucet on the taller tower has the same rate of flow as the smaller tower because they have the same difference of 'potential' from the point of highest potential (the top of the water column) to the point of lowest potential (the faucet's outlet).
If we increase or decrease the difference of potential (voltage/pressure) on the system and all else remains constant (the faucet remains fully open), the flow (current) will increase or decrease in proportion to the change in pressure. In other words, if you increase the pressure, there will be an increase in the amount of water flowing out of the faucet. It is the same in
an electrical circuit (without the faucet of course). When a given voltage
is applied to a given resistor (a simple electronic
device to be covered later) there will be a flow of current. If the voltage
is increased or decreased there will be a corresponding proportionate increase
or decrease in current.
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