The Potential Divider

Potential divider - circuit with voltage source and a couple resistors in series.
P.d of voltage source is divided into ratio of resistances: V1 / V2 = R1 / R2
You can choose resistances to get desired voltage.
V out = R2 / R1 + R2 X V in
Circuit used for calibrating voltmeters, which have V. High resistance.
Put something with relatively low resistance across R2- you start to have problems.
Effectively got two resistors in parallel, which will always have a total resistance < R2. Meaning V out < you’ve calculated + depends on what’s connected across R2.

V out varies with light or heat, you can make a potential divider that works as a light or heat sensor.
Circuit needs to be calibrated to know how voltage across component and V out varies as external conditions change.

Potentiometer has variable resistor replacing R1 + R2 but uses the same idea as a potential divider.
Move a slider or turn a knob to adjust relative sizes of R1 + R2. You can vary V out from 0 V up to input voltage, V in.
Handy when you want to change voltage continuously e.g. volume control of stereo.