Circuits / Getting started
Voltage divider
Vout = Vin · R2 / (R1 + R2), measured where the two resistors meet
Tap a part to see its voltages and currents. It is a model, not a measurement.
Predict, measure, explain
- Predict Two 10 kΩ resistors on 9 V: what voltage is at their middle?
- Measure Tap R2. Then change R2 to 20 kΩ.
- Explain
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Half, 4.5 V, because both resistors are equal. With 20 kΩ, R2 takes two thirds: 6 V.
What do you need?
- Resistor 10 kΩ × 2Search on Amazon
- Jumper wires × 2Search on Amazon
- BreadboardSearch on Amazon
How does a voltage divider work?
Two resistors in series share the supply voltage in proportion to their values. The output, taken where they meet, is Vout = Vin · R2 / (R1 + R2). Here two 10 kΩ resistors sit on 9 V, so each takes half: 4.5 V at the middle, with 450 µA flowing through both. Change R2 to 20 kΩ and it takes two thirds of the supply, 6 V, because it is now the larger of the two. The same current flows through both resistors, and the larger resistance drops the larger voltage. A divider is how a microcontroller reads a battery higher than its own supply, and it is the idea inside every potentiometer. One catch: anything you connect to the output draws current and pulls the voltage down, so a divider suits a high-impedance input, not a load like a motor.
Values from the Protoboard ISO simulation: a model, not a bench measurement.
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