Any child who has seen a metal detector in action knows how exciting it is when you find some buried treasure. Whether it’s real treasure or just a coin that fell out of someone’s pocket, it's a source of excitement that can be harnessed for learning. But professional-grade metal detectors and even build-your-own metal detector kits can be expensive. You may be surprised to learn that your child can make her metal detector with just a few, easy-to-find items.
Try this experiment!
What Your Child Will Learn
Through this activity, she will gain a simple understanding of how radio signals work. Learning how to amplify those sound waves results in a basic metal detector.
What You'll Need
- A small, battery-powered portable radio with AM and FM bands
- A small, battery-operated calculator (not a solar-powered one)
- Working batteries for both devices
- Duct tape
How to Make Your Own Metal Detector
- Switch the radio to the AM band and turn it on. It’s likely your child hasn't seen a portable radio before, so let her examine it, play with the dials and see how it works. Once she’s ready, explain to her that a radio has two frequencies: AM and FM.
- Explain that AM is the abbreviation for the “amplitude modulation” signal, a signal that combines audio and radio frequencies to create a sound signal. Since it uses both audio and radio, it’s very prone to interference, or signal blocking. This interference is not optimal when it comes to playing music, but it's a great asset for a metal detector.
- Turn the dial as far to the right as possible, making sure to find only static and not music. Next, turn up the volume as high as you can stand it.
- Hold the calculator up to the radio so that they are touching. Align the battery compartments in each device so that they are back-to-back. Turn on the calculator.
- Next, holding the calculator and radio together, find a metal object. If the calculator and radio are aligned correctly, you will hear a change in the static that sounds sort of like a beeping sound. If you don’t hear this sound, slightly adjust the position of the calculator on the back of the radio until you do. Then, move away from the metal, and the beeping sound should revert to static. Tape the calculator and the radio together in that position with the duct tape.
How Does It Work?
At this point, you've made a basic metal detector, but you and your child may still have some questions. This is a great learning opportunity. Start the conversation by asking her some questions, such as:
- What type of things does the metal detector react strongly to?
- Which things don’t cause a reaction?
- Why wouldn't this work if the radio was playing music instead of static?
The explanation is that the circuit board of the calculator emits a barely detectable radio frequency. Those radio waves bounce off metal objects and the AM band of the radio picks up and amplifies them. That’s the sound you’re hearing when you get close to metal. Music being transmitted over the radio would be too loud for us to hear the radio signal interference.