The Switch Is Off, But It Won’t Stop! Capturing the Mystery of Coil Oscillations with a Sensor (EasySense V-Hub)
I’m Ken Kuwako, a science trainer. Every day is an experiment.
The moment you flip a switch off, the current should drop to zero — or so you’d think. But a coil doesn’t give up that easily. It clings to the current like it has something to prove, sending voltage into a wild, oscillating frenzy. In this post, I’ll show you a demonstration experiment that makes this “stubbornness of coils” visible using sensors.
Circuit Setup and Preparation
I used a sensor to demonstrate electrical oscillation. The setup is simple: build the circuit shown below, run a current through a coil, then suddenly cut the switch. A voltage sensor then measures what the coil does next. I used the EasySense V-Hub for this.
Here are the sensor settings. In manual mode, set the measurement time to 200ms (100ms also works), the sampling rate to around 2000, and specify the trigger condition accordingly.
And Then… a Beautiful Wave Appeared!
Here’s a video of the actual experiment:
Even after the switch is cut, the current doesn’t vanish instantly — you can clearly see the voltage fluctuating due to the coil’s influence. And the waveform that appears is genuinely beautiful: a clean, smooth wave that looks like it was lifted straight from a trigonometry textbook.
This is the phenomenon known as self-induction.
When current tries to change abruptly, the coil pushes back — generating an electromotive force in the opposite direction, as if to say, “Not so fast.” This behavior comes from a property called inductance. When paired with a capacitor in what’s called an LC circuit, it produces sustained electrical oscillations — the very same principle that allows a radio to tune into a specific frequency.
Place Iron on the Coil… and the Period Changes
When you place a piece of iron on top of the coil to increase its self-inductance, the period of oscillation changes noticeably. You can see the spacing between waves shift. A larger inductance means slower oscillations — just like how a heavier pendulum swings more slowly. It turns out the electrical world has its own version of “mass.” Once you see it that way, physics starts to feel a whole lot more interesting, doesn’t it?
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