Passives

Potentiometer

A resistor with a third contact, the wiper, that slides along it. Connected across a voltage it is an adjustable voltage divider: the wiper picks off any voltage between the two ends.

Think of it as: A tap on a pipe with a side outlet: turning it chooses how much of the pressure reaches the outlet.

Pins

1 and 3 (ends): : The full resistance is always between these two.
2 (wiper): : The middle pin. Its resistance to each end changes as you turn the knob.

Knob pots (volume controls) have a shaft; trimmers are tiny pots you set once with a screwdriver. The value printed is the end-to-end resistance, such as "B10K" (linear, 10 kΩ).

What to look for inside

This shows the track between pin 1 and the wiper while the knob slowly turns from one end to the other.
Turning the knob changes how much of the resistive track the current has to cross before reaching the wiper.
Less track means less resistance, so more current and more heat in the part that is left. Near the end of travel the current is at its highest.

The numbers that matter

Spec	Typical
Resistance End to end. 10 kΩ is the most common.	1 kΩ to 1 MΩ
Taper How the resistance follows the rotation (see the curve).	B = linear, A = log
Power rating Pots are fragile: keep the current through the wiper small.	0.05 W to 0.5 W

Where you’ll use it

Volume and tone knobs.
A control input: the wiper voltage goes to a microcontroller’s ADC pin and the program reads the knob position.
Trimming a circuit once, for example setting a reference voltage or LED brightness.

Common mistakes

Using the pot itself to carry a big load current. Use it to set a voltage, and let a transistor or regulator do the heavy work.
Turning it to one end with nothing else in series. The resistance can drop to almost zero and short the supply.

Lessons that use it

No lesson uses a pot yet. A pot is a voltage divider you can turn, which lesson 2.1 covers.

Lesson 2.1: Voltage Dividers & the Loading Effect

Go deeper

U_{wiper} = U_{in}\,\tfrac{R_{2}}{R_{1} + R_{2}}

R₂ is the wiper-to-ground part of the track, R₁ the rest.

R_{1} + R_{2} = R_{pot}

The two parts always add up to the full value.

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