## Intro

Resistors can be placed in series (end to end), in a circuit like the following: Diagram of a circuit showing a source voltage connected to three resistors connected in series, labeled R1, R2, and R3.

In this case, the total resistance is the sum of each resistor. So for instance, given the following resistors:

• R1 - `100Ω`
• R2 - `5Ω`
• R3 - `1kΩ`

Then the total resistance would be:

``````Total Resistance = 1,000Ω + 100Ω + 5Ω = 1,105Ω
``````

## Common Current, Different Voltage

Resistors in a series share a common current, that is the amount of amps flowing through each one is the same, since there’s only one path.

So for instance, given the previously calculated resistance of `1,105Ω`, if we were to supply `5V` of electrical force, we can use Ohm’s law to calculate the current at any given point as:

``````I = 5V / 1,105Ω = 0.004A = 4mA
``````

So no matter where in the circuit that we measure the current, we would get the same value of `4mA`: Diagram of a circuit showing a source voltage connected to three resistors connected in series, labeled with 100 ohms, 5 ohms, and 1 kiloohm.

### Power Calculation

Given that we know the current and resistance at any resistor in a series, we can use the `P = I^2 * R` form of the power law we derived earlier from Ohm’s law and the definition of the watt. However, since there are multiple resistors in the series, we add an `n` to specific power and resistance at resistor number `n`:

``````Pn = I^2 * Rn
``````

### Voltage Division

Although the current at any given point in a series circuit is the same, the voltage drops as it passes through each component as the electromagnetic force is resisted. Because of this, resistances in series forms the fundamental circuit for voltage division, which we’re going to explore more thoroughly in part 5 of this tutorial.