Light Made the Electricity Vanish!? Experience Einstein’s Greatest Discovery with a Gold-Leaf Electroscope
I’m Ken Kuwako, the Science Trainer. Every day is an experiment.
“Just shine light on it, and the electricity disappears.”
It sounds like magic, but this strange phenomenon really happens in the lab. Even more fascinating, it’s directly connected to the discovery that earned none other than Albert Einstein a Nobel Prize. Today, let’s explore this mysterious experiment using a gold-leaf electroscope.
What Is a Gold-Leaf Electroscope?
A gold-leaf electroscope is a device used to detect static electricity (electric charge). Inside are two thin metal leaves hanging side by side. When electric charge builds up, the leaves repel each other and spread apart.
In this experiment, we begin with the leaves already open. That means the electroscope is storing electric charge.
What Happens When Ultraviolet Light Hits It?
Next, we shine ultraviolet light onto the metal plate at the top of the charged electroscope.
And then—something incredible happens.
The leaves slowly begin to close!
Take a look at the video below to see it in action.
It almost looks as if the light itself is sucking the electricity away. So what’s really happening?
The Secret Behind the “Photoelectric Effect”
This phenomenon is called the photoelectric effect. When light—especially short-wavelength light like ultraviolet rays—hits a metal surface, electrons can be ejected from the metal.
In this experiment, the electroscope had accumulated negative charge, meaning extra electrons were stored on it. When ultraviolet light struck the metal plate, electrons began flying off the surface one after another. As the stored charge decreased, the leaves gradually closed.
In other words, the light was literally knocking electrons loose from the metal.
The Surprising Link to Einstein’s Nobel Prize
The photoelectric effect turned out to be one of the biggest scientific mysteries of the late 19th century. At the time, scientists couldn’t fully explain it using the idea that light behaved only as a wave.
Then came Albert Einstein.
In 1905, Einstein proposed a revolutionary idea: light is made up of tiny packets of energy called photons. This bold theory perfectly explained the photoelectric effect.
That achievement is exactly why Einstein received the Nobel Prize in Physics in 1921.
Surprisingly, it wasn’t relativity that won him the Nobel Prize—it was his explanation of light itself.
The Photoelectric Effect Powers Modern Technology
The photoelectric effect isn’t just a topic from old physics textbooks. It forms the foundation of many modern technologies we use every day.
For example, solar panels generate electricity by using light energy to move electrons—an application of the photoelectric effect.
The image sensors inside smartphone and digital cameras also rely on this principle, converting light into electrical signals.
Hidden inside that simple experiment—watching thin metal leaves slowly close—is one of the key pieces of physics supporting modern civilization.
By simply shining ultraviolet light onto a gold-leaf electroscope, you can witness a glimpse of Einstein’s groundbreaking realization that “light behaves like particles.”
Watch the video carefully and observe the exact moment the leaves begin to close. You’ll be seeing one of the greatest discoveries in physics unfold right before your eyes.
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５月のイチオシ実験！
キーンと冷えるドライアイス！気温が上がってくるこの時期・ドライアイスを使った昇華・凝結・等速度直線運動の実験はいかが？
液体ゼロ！ドライアイスが消えるまでの３時間を科学する（昇華・凝結・等速度直線運動）
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