Ohm's Law

The relationship between current, voltage, and resistance is defined by Ohm's Law:

The current flowing from one point to another is equal to the voltage accross these points divided by the resistance between them.

I = \frac{V}{R}

As an application, consider a circuit with a 9V battery with a 10,000 \Omega resistor attached across its terminals.

The current flowing through the resistor can be calculated as follows:

\frac{9V} {10,000\Omega} = 0.0009 \textsf{A} (0.9 \textsf{mA})