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Ohm's Law
A simple resistance circuit.

One thing we need to be able to do when we see a schematic circuit diagram is to perform mathematical calculations to define the precise behavior of the circuit. All information required to perform such calculations should be included on the schematic diagram itself. That way the information is all in one place, and any required detail can be determined readily.

Consider the basic circuit shown to the right. We know immediately that the battery voltage is 6 volts and that the resistor is rated at 1000Ω. Now, how can we determine how much current is flowing through this circuit?



If you go back to Basic Circuit Concepts, you'll note that the relationship between voltage, current, and resistance is given as E = I × R. Using basic algebra we can also rewrite this as:

These three equations describe Ohm's Law, which defines this relationship.


In the circuit shown above, we see that E = 6 volts and R = 1000Ω. To find the current flowing in this circuit, we must select the equation that solves for I. Using that equation, we note that:

    I = E ÷ R

    I = 6v ÷ 1000Ω

    I = 0.006 ampere (A) = 6 milliamperes (mA)


All calculations involving Ohm's Law are handled in exactly the same way. If the circuit gets complex, the calculations must be tailored to match. However, each calculation is still just this simple.


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