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In Book 2, Chapter 2, you take a closer look at resistors and also take an in-depth look at Ohm’s law, which is one of the most important mathematical relationships in electronics. But without going into all the details of Ohm’s law here, I want to at least give you a sneak preview.

Ohm’s law describes a fundamental relationship between current, voltage, and resistance in an electrical circuit. Remember from Chapter 2 that voltage is a difference in electrical charge between two points, and that if those two points are connected by a conductor, current will flow through the conductor.

Other than exotic superconductors (which exist only in laboratory experiments), no conductor is perfect. All conductors have a certain amount of resistance that inhibits the flow of current. The greater this resistance, the less the current will flow. The less this resistance is, the more the current will flow.

Ohm’s law is a mathematical formula that formalizes the relationship between current, voltage, and resistance. The formula is this:

In other words, the amount of current running through a circuit is equal to the amount of voltage across the circuit divided by the amount of resistance in the circuit. The amount of current in amperes is represented by the letter I (don’t ask why; it just is). V represents voltage in volts, and R represents resistance in ohms.

Using basic math, you can use this equation to calculate the voltage if you know the current and the resistance. Then, the formula becomes:

In other words, voltage is equal to current times resistance.

Similarly, you can calculate resistance if you know the current and the voltage. Then, the formula becomes:

In other words, resistance equals the voltage divided by the current.