Vol. DIY Electronics Projects

Chapter 4 AC Circuit Projects

AC Lab - Variable Inductor

In this hands-on AC electronics experiment, build a variable conductor and learn the impact of a metal core placed inside an inductor coil has on the inductance.

Project Overview

In this project, the construction of the simple variable inductor circuit, illustrated in Figure 1, will help you learn more about inductors.

Variable inductor circuit.

Figure 1. Variable inductor circuit.

As you will experience, the placement of the steel bar affects the inductance of the wire coil and, therefore, the light through the lamp.

Parts and Materials

Paper tube from a toilet paper roll
Bar of iron or steel, large enough to almost fill the diameter of a paper tube
28 gauge magnet wire
Low-voltage AC power supply
Incandescent lamp, rated for power supply voltage

Learning Objectives

Determine the effects of magnetic permeability on inductance.
Determine how inductive reactance can control current in an AC circuit.

Instructions

Step 1: Wrap hundreds of turns of the magnet wire around the paper tube.

Step 2: With the paper tube empty, connect this homemade inductor in series with a low-voltage AC power supply and lamp to form a circuit, as illustrated in Figures 1 and 2.

variable inductor schematic diagram

Figure 2. Variable inductor circuit schematic diagram

You can use the low-voltage supply described in the earlier AC project, Using a Transformer to Build a 12 VAC Power Supply. When the tube is empty, the lamp should glow brightly.

Step 3: Insert the steel bar into the tube. The lamp dims from the increased inductance (L) and consequently increased inductive reactance (X_L).

Step 4: Try using bars of different materials, such as copper and stainless steel, if available. Not all metals have the same effect due to differences in magnetic permeability.