# electrical equations

From Noah.org

P = E^2 / R

## Contents

# Voltage Divider

## Voltage Divider No Load

The voltages are proportional to the resistances.

Vout = Vin * (R2 / (R1 + R2)) Vin = Vout * ((R1+R2)/R2)

Vout+ O Vout- O | | | | R1 | R2 | +--/\/\/--+--/\/\/--+ | | | | Vin+ Vin-

## Voltage Divider Under Load

R2 || Rload = (R2 * Rload) / (R2 + Rload) Vout = V1 * ( R2 ||Rload) / (R1 + R2 || Rload)

Rload +--/\/\/--+ | | | | Vout+ O Vout- O | | | | R1 | R2 | +--/\/\/--+--/\/\/--+ | | | | Vin+ Vin-

Vout = Vin (

## Picking a value for R1 and R2

Assume you have a restive sensor to test. Out of circuit you would test the sensor to determine its minimum resistance and maximum resistance. Then pick

R2 = sqrt (Rmin * Rmax)