Don't let it confuse you. Short Refresher Course Change of Resistance: In the following diagram, you can see that the only difference between the diagrams on the left and the diagrams on the right is the resistance in each 'system'. The resistance in the faucet corresponds to the amount that the valve is open. What you should note in this diagram is... All else being equal, if there is an increase in resistance, the current flow will be reduced. You can see that the current flow in the rightmost wire is half of the current flow in the leftmost wire. This is because the rightmost wire has half of the area for the electrons to pass through. There is no physical restriction in a real piece of wire. Change of Voltage: In the following diagram, you can see that the resistance in all of the systems is equal. You can see that the increased voltage causes an increase in current even though the resistance in both the left and right systems is equal. Mathematical Example: In the following example, we know that we have 12 volts applied to a 10 ohm resistor. If you want more examples, the page has more fun than a barrel of monkeys. If you want to try a few for yourself, the calculators below will allow you to check your math. Find: Power dissipation and Current flow from Resistance and applied Voltage. Data Input: Power Dissipation? Changing either one will change the current flow and power dissipation in the circuit. You should realize that an amplifier produces a voltage into a given load. The combination of the two will result in power dissipation in the speaker's voice coil in the case of audio. Since an amplifier can produce a limited amount of voltage limited by the internal power supply's design , the power output is limited when driving a given load i. To be able to produce more power, you can drive a lower impedance resistance load within reason. This means that if you go from a 4 ohm load to a 2 ohm load, the power will double assuming that the power supply is regulated. If we use the example of a 100 watt mono amplifier 100 watts into a 4 ohm load , we know it can produce no more than 20 volts across the speaker. If you set the voltage slider below to 20 volts, and the resistance slider to 4, you can see that the power is 100 watts. If you move the resistance slider to 2 ohms, you can see that the power is doubled to 200 watts. Now, I know that I'm showing a battery as the voltage source instead of an amplifier but the concept is the same. Click to make this applet fill this window. Historical Information Georg Simon Ohm: Georg Simon Ohm was a German physicist that lived from 1789 to 1854. He found that, with a constant resistance, voltage and current were directly proportional as we showed in a graph above. James Watt: James Watt was a Scottish inventor that lived from 1736 to 1819. The unit of measure for power, the watt, was named in his honor. James Prescott Joule: James Prescott Joule was an English physicist that lived from 1818 to 1889. He discovered the relationship between the power dissipated in a resistor and the current flow through the resistor. Ohm is generally given credit for the formulas which express the relationship between Power, Current, Resistance and Voltage but the credit probably should go to Joule. The 'Joule' as a unit of measure: A 'Joule' represents the amount of energy used when 1 watt is dissipated for 1 second or 1 watt-second. You should remember: 1. If you have any 2 of the 4 electrical properties, you can find the other properties through Ohm's law. Click to visit a friend's new car audio tech site.
