Shocking Truth: Can Humans Conduct Electricity? Let’s Try the Human Circuit Experiment! [Tamesu-kun]
I’m Ken Kuwako, your Science Trainer. Every day is an experiment!
Today, we’re diving into something a little different from static electricity. We’re going to try running a tiny electric current through the human body! You might be wondering, “Wait, through my body?” But with a simple gadget, you can actually see the current flow as it lights up a bulb.
What is the “Tamesu-kun” Pencil Circuit Tester?
One of my favorite tools is called “Tamesu-kun” (meaning “The Little Tester”). It was developed by Mr. Kawakami, a senior of mine from university who now runs an educational materials company. It’s a clever combination of two lithium coin batteries (6V total) and an LED. Since it’s so simple, you can even DIY one at home! If you’d rather buy the official version, you can find it right here. This little device opens up a world of experimental possibilities.
Tokyo Science Education Institute: Tamesu-kun
Let’s Create a Human Circuit!
Here’s a sudden question for you: Can electricity actually flow through a human? And if it does, can you feel it? Take a look at this video.
What did you think? If we place Tamesu-kun on plastic…
Nothing happens. But if we touch it to the metal part of a pair of scissors…
It lights up! Now, what if one side touches plastic?
No light. Let’s try aluminum foil.
It glows! This confirms that metal conducts electricity. Now, here is the exciting part—what about humans? If I hold it between my fingers…
It lights up! At this moment, a circuit is formed from the right hand, through the body, to the left hand. A very weak current is flowing, yet I don’t feel any pain at all. You can even do it like this:
This works because a circuit is formed between the index and middle fingers. I also tried making a circuit out of aluminum foil and “bridging” a gap with my hand—it still lights up!
I even tried holding hands with a child, and the light stayed on.
Fascinating, isn’t it? If we let go, the light turns off. It worked with four people, and even when I tried it with 32 students in class, it still lit up! Truly amazing.
When I explain how body fat scales work to my students, I tell them that current flows through the body, but it’s often hard for them to really “feel” it as a reality. With Tamesu-kun, their reaction is completely different. But if there’s current flowing, why isn’t it painful? Look at this data:
Source: Ryuji Tanaka & Kenji Ichikawa, “Industrial Safety Research Institute Safety Data RIIS-SD-70-1” (Ministry of Labour) (*1)
For direct current (DC), we usually start feeling it at around 3mA (0.003A). I decided to measure the actual current flowing through Tamesu-kun.
Typically, LEDs have an optimal voltage of around 2V. Is 6V safe? First, I measured the current of Tamesu-kun alone. It was about 87mA. While this exceeds the “optimal” rating, it’s not high enough to instantly burn out the device.
The secret lies in the lithium coin batteries. These batteries have a high internal resistance, which acts as a natural limit on the current. Next, I measured the current when I became part of the circuit. The result…
Only 20.2μA (0.02mA)! It’s incredibly safe, and the fact that an LED can light up with such a tiny current is mind-blowing. Once the flow starts, the LED’s properties keep the resistance low, allowing it to stay lit.
Let’s Draw a Pencil Circuit (First Lesson of Electric Circuits)
In my introductory class on electric circuits, I use Tamesu-kun to help students figure out what makes a circuit work. First, I let them draw whatever they want.
When we place Tamesu-kun on the graphite lines, the LED glows!
I then challenge them: “How can we make the light brighter?” Students start experimenting with all sorts of drawings.
Their observations are spot on:
Make the path shorter.
Make the path thicker.
Make the lines darker (more graphite).
For example, look at this pencil-drawn circuit:
As we slide the device further up…
And further…
The LED gets brighter and brighter! This is because the circuit gets shorter, which lowers the resistance. Of course, touching it to a direct conductor makes it dazzlingly bright.
It’s almost too bright given the 6V supply, but look at that glow! Let’s try a parallel circuit next.
The light intensifies step-by-step. Even if students have memorized the formulas for parallel resistance, many are surprised to see it in action. Then, we tried thickening the lines.
The resistance drops, and the brightness peaks. It’s a perfect visual way to understand that a thicker “wire” equals less resistance. And yes, even a standard pencil conducts electricity!
[Special Feature] Irresistible! Static Electricity Experiments
Next, let’s move on to an experiment about how to draw circuit diagrams.
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