# Derivation of formula for resistors in parallel

## The voltage across each resistor is the same as the battery voltage

Animation explaining how the formula for the effective resistance of parallel circuits is derived.

##### Practise past papers and get Better Grades!

Visit our sister site www.good-at-maths.com for

- PAST PAPERS
- MODEL ANSWERS
- HD VIDEO EXPLANATIONS

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

This is the strategy

- write an equation saying: current drawn from the battery = sum of the currents through each resistor
- write V/R instead of I
- use the fact that the voltage across each resistor is the same as the battery voltage
- divide by V all the way through since it's the same both sides, which leaves us our expression in R