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



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 (XL).

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.


Related Content

Learn more about the fundamentals behind this project in the resources below.





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