Describe the action of a variable potential divider

4.3.3 Action and Use of Circuit Components – Variable Potential Divider

What is a Variable Potential Divider?

A variable potential divider is a simple circuit that splits an input voltage into a smaller, adjustable output voltage. Think of it like a sliding scale on a dimmer switch: by moving the slider, you change how much of the light (voltage) reaches the bulb (load). The most common component used is a potentiometer – a three‑terminal resistor whose resistance can be changed by turning a knob or sliding a contact along a resistive track.

How It Works

The potentiometer has two outer terminals that connect to the input voltage \(V_{\text{in}}\) and ground. The middle terminal (wiper) is the output. By sliding the wiper, you change the ratio of the two resistances \(R_1\) and \(R_2\) that form a series chain. The voltage at the wiper is given by the voltage divider rule:

$$V_{\text{out}} = V_{\text{in}} \frac{R_2}{R_1+R_2}$$

When the wiper is at the left end, \(R_2\) is almost zero and \(V_{\text{out}}\) ≈ 0 V. When it’s at the right end, \(R_1\) is almost zero and \(V_{\text{out}}\) ≈ \(V_{\text{in}}\). In between, you get any voltage between 0 V and \(V_{\text{in}}\).

Practical Example – Light‑Level Sensor

Suppose you want to dim a LED using a variable resistor. Connect a 10 kΩ potentiometer across a 5 V supply. The LED sits between the wiper and ground. Turning the knob moves the wiper, changing \(R_2\) and thus the LED current. When the wiper is near ground, the LED is bright; when it’s near the supply, the LED is dim. This is a classic use of a variable potential divider in everyday electronics.

Key Points (Quick Review)

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