# Quick Reference

## Series Resistance Calculation

```
Total R = ∑(R1...Rn)
```

# More Info

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
```

# Further Reading

For a more in-depth discussion about resistors and resistance, check out Part 4 of the Electronics Tutorial.