Voltage division can be applied when two resistors are in series. This is because of Kirchhoff's Voltage Law must hold true for a closed loop, and since the closed loop has the same current throughout, the voltage through each branch
| V1 = VsR1/(R1+R2) | V2 = VsR2/(R1+R2) |
| because... | because... |
| V1 = IR1 | V2 = IR2 |
| Vs = I(R1+R2) | Vs = I(R1+R2) |
| I = Vs/(R1+R2) | I = Vs/(R1+R2) |
| V1 = VsR1/(R1+R2) | V2 = VsR2/(R1+R2) |