## Quick Reference

### Series Resistance Calculation

``````Total R = ∑(R1...Rn)
``````

Resistors can be placed in series (end to end), in a circuit like the following:

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
``````

## Calculation

Therefore, the equation to calculate total series resistance is as follows:

``````Total R = ∑(R1...Rn)
``````

## 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 there is a `5V` supply of electrical force, Ohm’s law can be used to calculate the current at any given point as:

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

So no matter where in the circuit that current is measured, it would be `4mA`:

### Power Calculation

The `P = I^2 * R` form of the power law can be used to calculate the power at any resistor (`n`) in a series:

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