ohm'slawwithatwist.

Ohm's Law with a twist.

Here's what happens to the simple Ohm's Law pie chart when the power variable is added. Ohhhhh... Good stuff!

Ohm's Law describes the interworking relationship between the voltage across, the current flowing and resistance contained in a given electrical circuit. A change of value in any one of these variables will effect a change in one or more of the others.

Ohm's Law applies to all electrical circuits but is most simply and obviously applied to those carrying Direct Current (DC).

The basic formula representing Ohm's Law is expressed as voltage (E) equals current (I) multiplied by resistance (R) or E = I R.

As long as any two of these variables are known the third can be found by manipulating the above equation.

Rather than go through the algebra that may be needed to do so the chart below was developed to provide an easy visual reference in finding which manipulation of the Ohm's Law equation to use.

Note: Be sure to use like values in the above equations. In other words be aware of unit multipliers (kilo, Mega, milli, micro, etc.). For example 1 kilohm would be 1000 ohms and 1 milliamp would be .001 amp. It is simpler to keep numerical values straight by converting prefixed units such as the examples above to "basic units" by doing the math needed to remove any multiplier before performing calculations. (That's clear as mud, right?)

Another equation exists that's used to find the power, in Watts, consumed in an electrical circuit. That equation is power (P) equals voltage (E) multiplied by current (I) or P = E I.

Again, algebra can be used to find any one of the three variables in the above power equation as long as the other two are known.

BUT... What happens when the variable of power is introduced in to Ohm's Law? The equations E = I R and P = E I can be combined with each other in many permutations. It gets pretty messy!

With the handy but somewhat complex chart below one can find power, current, resistance or voltage by plugging the known values in to the needed formula.

In this chart perform the operation available in the quadrant of the circle labeled with the value for which you are solving. For example, if power (P) is the value you wish to calculate the three operations in the upper left quadrant of the chart are available, depending on which two variables are known. Again, be aware of unit multipliers before performing calculations.

Will you ever need to know this stuff? Very probably not, unless you're big into circuit design or something (aren't we all?).

It just shows a really interesting relationship between voltage, current, resistance and the power consumed in an electrical circuit most folks never consider.

The always required disclaimer:

The above Ohm's Law charts have been put up on the web as a demonstration of the interaction between variables of a direct current (DC) electrical circuit. The author of this page is aware that applying these equations to alternating current (AC) circuits often requires the understanding and application of AC circuit theory, such as the effect of phase differences between current and voltage in AC circuits. It's also understood that impedance would be substituted for resistance in the AC world, and on and on. That stuff goes well beyond the scope of this page, however. Plus, it's been so long since I messed with all of that I barely remember what I forgot about it. Anyway, this page is here only because I happened to have an interesting chart I thought would look cool on my site, so this is where it found itself ;-)

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