# Which is the second resistor in a voltage divider?

The formula for a voltage divider is:

Voltage out = ( resistance two/resistance one + resistance two ) * voltage in

or Vo = ( R2 / R1 + R2 ) * Vi

How do you identify the R1 resistor? Is it the one which conventional current 'goes through' first?

• you just choose which one you want to know the voltage over. Typically this is the one over which your load is connected in parallel. – JMLCarter Jan 23 '17 at 10:17
• Why the down vote? What is wrong about this question? – Mirte Mar 21 '17 at 8:37
• it wasn't my dv. – JMLCarter Mar 21 '17 at 19:52

The voltage divider formula is used where there is a series of two resistor and you want to know the voltage through one of the two. The voltage drop of the resistor number 1 is $$V_1 = V_i \frac{R_1}{R_1 + R_2}$$
The voltage drop of the resistor number 2 is: $$V_2 = V_i \frac{R_2}{R_1 + R_2}$$