# Finding voltages in series using ratios

## Resistor voltage: battery voltage = resistor resistance: total circuit resistance

Animations explaining how to use proportion to calculate voltage in series circuits.

We know that in a series circuit the biggest resistance takes the biggest share of the battery voltage. We can use this idea to calculate how the voltage is shared without having to use V = IR at all.

V:V_{battery} = R:R_{effective}

The ratio sign is equivalent to division so

V/V_{battery} = R/R_{effective}

rearranging we get

V = V_{battery} x R/R_{effective}

If you only have two resistors then once you've calculated one voltage you can just use the idea that the total voltage equals the battery voltage to find the other.