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 Flash demo below, the valve will be analogous to 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 because the resistance to the flow is very low. For best results, press the buttons alternately (up, down, up, down...). The valve in the upper right hand corner shows the position of the gate in the valve on the pipe.

Remember, Pressure = voltage

Now let's say that the valve position is constant (partially 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. For best results, press the buttons alternately (down, up, down, up...).

Remember, Pressure = voltage

Note:
In car audio, resistance plays a vital role. When wiring speakers, you must have a safe load resistance to avoid destroying your amplifier. Read on to learn more on proper wiring of speakers, head units and amplifiers.

Now go back to the voltage section and reread all pages up to this point. After reading the pages for the second time go to the next page (don't get caught in an endless loop :).