# Derivation of formula for resistors in series

## The current through each resistor is the same as the current through the battery

Animations walking you through the derivation of the formula for the effective resistance of resistors in series.

Let's see if we can derive the equation for finding the effective resistance of series circuits.

This is the strategy

- write an equation saying: battery voltage = sum of the voltages across each resistor
- write IR instead of V
- use the fact that the current through each resistor and the battery is the same since they're all in series
- divide by I all the way through since it's the same both sides, which leaves us our expression in R