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RESISTANCE
Resistance is the measure of a device's
opposition to the flow of electrical current.
Its unit of measure is the ohm. If a device with one ohm of resistance
is connected across a one volt power supply, the flow
of current through the device will be limited to one amp.
If the resistance is doubled, and the power supply voltage remains at one
volt, the current flow will be one half amp. As you can see, more "resistance"
will reduce the current flow in the circuit (if voltage remains constant).
In the diagram below, the valve will be the resistance in the water distribution system. For this example the pump will again produce a constant pressure before the valve. When the valve is almost closed, the resistance is high. The resistance to the flow of water is high therefore the current flow is low. When the valve is completely open, the flow of water is very high. The resistance to the flow is very low.
Remember, Pressure = voltage.
Now let's say that the valve position is constant (half open) but the pressure that the pump applies to to the valve is going to vary. When the pressure (voltage) is high, the flow through the valve is going to be high. At moderate pressure the current flow will be moderate and of course when the pressure (voltage) is low the current flow will be low.
Remember, Pressure = voltage.
You should remember:
1.Resistance is the opposition to the flow of electrical current.
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