The next formulas are used to calculate the voltage across resistors in a series association or voltage divider as shown bellow.
Formulas 1
V1 = V x [ R1 / (R1 + R2) ] (a)
V2 = V x [ R2 / (R1 + R2) ] (b)
Where:
V is the voltage applied to the divider in volts (V)
V1, V2 are the voltages across the resistors R1 and R2 in volts (V)
R1, R2 are the resistances in ohm (Ω)
Application Example:
Two resistors (R1 = 20 ohm and R2 = 30 ohm) are wired as a voltage divider and plugged to a 10 V power supply. Calculate the voltage across R1.
Data:
R1 = 20 Ω
R2 = 30 Ω
V1 = 10 Ω
V2 = ?
Using formula 1 (b):
V2 = 10 x (30/(20 + 30))
V2 = 20 x 30/50
V2 = 4 volts
