Magnets Dance in a Paper Cup! Discover How Speakers Work with a Homemade Wire
I’m Ken Kuwako, a Science Trainer. Every day is an experiment.
“An invisible magnetic field carrying sound through the air.”
Have you ever experienced something that felt almost like magic?
The other day, while visiting the science museum Tsukuba EXPO Center, I came across an exhibit that made me stop in my tracks. It was a fascinating speaker that used a coil. Simply holding the coil-equipped speaker in the invisible magnetic field coming from the base allowed you to hear sound through electromagnetic induction.
Move it farther away, and the sound becomes faint. Bring it closer, and the sound suddenly gets much louder. We may understand in theory that a magnetic field can generate an electric current across empty space, but actually experiencing it is so fascinating that you can’t help saying, “Wow!”
This time, I’d like to show you how to recreate this “electricity jumping through space” at home. The star of the show is a homemade magic wire called the Pascal Wire, which you can make with materials from a dollar store and a little ingenuity.
It is a homemade experimental device made by taking advantage of a cable containing multiple bundled wires, such as a 10-core cable. Making it requires some soldering, but once you’ve built it, it is inexpensive and remarkably effective.
The Science Recipe
What you’ll need:
Pascal Wire (homemade) Paper cup Neodymium magnet (small but powerful)
Steps:
Connect the Pascal Wire to an AC power supply.
Wind the wire into a coil about the same size as the bottom of the paper cup.
Place the neodymium magnet inside the paper cup.
Once everything is ready, turn on the AC current and carefully watch what happens inside the cup.
Experimental Results: A Dancing Magnet and a Mysterious “Sound”
I recorded the experiment on video. Be sure to turn up the volume before playing it!
What did you think? The moment you switch it on, you can see the magnet start dancing inside the paper cup, almost as if it has a mind of its own.
What’s Going On? Why Does the Magnet Dance?
Why did the quiet, motionless magnet suddenly start going wild? The secret lies in the combination of “AC” and an “electromagnet.”
The magnetic field created by the electric current makes the magnet vibrate.
The electricity supplied through the outlets we use every day is “alternating current,” or AC. Unlike “direct current,” or DC, from a battery, the direction of the current repeatedly switches back and forth. In Japan, this happens 50 times per second in eastern Japan and 60 times per second in western Japan. That is incredibly fast!
When current flows through the coil made from the Pascal Wire, it becomes an “electromagnet.” So what happens when AC flows through it? Exactly! The electromagnet’s north and south poles switch back and forth dozens of times every second.
Place a neodymium magnet on top of this electromagnet, whose poles are switching at tremendous speed, and the magnet is alternately “pulled toward” and “pushed away” over and over again. As a result, the magnet vibrates rapidly, making it look as though it is dancing.
The “Heartbeat of AC” and How a Speaker Works
Now firmly attach the vibrating magnet to the bottom of the paper cup using vinyl tape or something similar, and put your ear close to the cup.
Can you hear a low “buzzing” sound?
That sound is produced when the tiny vibrations of the magnet shake the bottom of the paper cup, which in turn makes the surrounding air vibrate. It is, quite literally, the heartbeat of alternating current.
By the way, the pitch of the sound is determined by how many times the magnet vibrates each second. There is a difference between the 50 Hz electricity used in eastern Japan and the 60 Hz electricity used in western Japan—roughly the musical interval between C and E♭. The sound should therefore be slightly higher in western Japan. If you ever get the chance to try this experiment in both regions, comparing the sounds could be fun!
And here’s the really interesting part: this is essentially how a speaker works!
The music we listen to every day originally exists as “complexly changing electrical signals (AC).” These signals are sent through a coil inside a speaker, and the interaction between the coil and a magnet makes the speaker diaphragm vibrate. Those vibrations are then transmitted through the air to our ears as sound.
The exhibit at Tsukuba EXPO Center that I mentioned at the beginning was essentially demonstrating this process in reverse. In other words, it allowed visitors to experience electromagnetic induction—the phenomenon in which moving a coil through a magnetic field generates electricity—as sound.
A paper cup, a magnet, and some homemade wire. With such simple materials, you can see and feel the basic mechanism behind a speaker, one of the symbols of modern technology. That, to me, is one of the great joys of science.
With just a little time and curiosity, anyone can listen to the “voice” of electricity. Why not try experiencing the heartbeat of AC for yourself at home?
Questions, Requests, and Collaborations
Want to bring the wonders and excitement of science a little closer to everyday life? I share fun science experiments you can try at home, along with simple tips and explanations. Have a look around and search for whatever catches your curiosity!
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