How Does It Charge Just by Sitting There? We Took a Wireless Charger Apart!
I’m Ken Kuwako, your science trainer. Every day is an experiment.
Just set your smartphone on a wireless charger, and it starts charging. No cable, no plugging and unplugging. It feels like magic, but when you pop the lid open, you’ll find a part you probably remember from science class.
Let’s Take a Wireless Charger Apart
So, what’s really going on inside a wireless charger? Let’s crack one open and find out.
Before the Teardown: It Really Does Charge Your Phone
Here’s the wireless charger before I took it apart. If you set your smartphone on top, it charges just fine. It looks like nothing more than a flat, round disc, but the secret to how it works is hidden inside.
Time to Open It Up! What’s Under the Lid?
Okay, let’s do it. As I unscrew the lid, I can’t help wondering what’s going to be inside. The suspense is real!
The Mystery Part Is a Coil!
With the lid off, a coil appeared. It’s simply a wire wound round and round in a spiral. Many of you may remember a junior high science experiment where you moved a magnet in and out of a coil to generate an electric current. This is basically a close relative of that very same coil.
Electricity Doesn’t Fly Through the Air
Here’s what happens: a high-frequency alternating current runs through the coil in the charger, creating a magnetic field. That field causes electromagnetic induction in the coil inside your smartphone, and that’s what charges it.
The important thing to understand is that the electricity itself isn’t flying through the air. Let’s go through it step by step.
First, an alternating current, which rapidly flips its direction back and forth, flows through the charger’s coil. This creates a magnetic field around the coil that keeps flipping direction too. Then, when that changing magnetic field passes through the coil inside your phone, electromagnetic induction generates a current in the phone’s coil. That current is what charges the battery.
The key here is that the magnetic field keeps on changing. Remember how a magnet sitting still inside a coil produces no current, but moving it does? It’s the same idea. By using alternating current, the charger keeps the magnetic field changing nonstop.
Think of It as a Relay Race for Electricity
You can picture it like two people standing far apart who never hand a ball directly to each other. Instead, they pass energy along using a “magnetic field” as the baton. Isn’t it neat to think that the electromagnetic induction experiment you learned in school is hard at work inside the smartphone you use every day? Science suddenly feels a lot closer to home, doesn’t it?
By the way, if you don’t place your phone right in the center of the charger, it may charge slowly or stop altogether. That’s because when the two coils are out of alignment, the magnetic field doesn’t transfer as well. Some electric kettles and electric toothbrushes also use this same kind of electromagnetic induction charging.
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Science is full of wonder and fun, and it’s closer than you think! This site collects enjoyable science experiments you can try at home, along with tips for getting them right. Try searching around and see what you find!
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- 「ネイチャーティーチャー」（TBS）に出演しました。Tverにて11月3日（火）まで配信中です。
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- 11月4日（水） ZIP（日本テレビ）7:20頃放送予定（科学監修）
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- 『高校入試 分解問題集 理科』（学研）…難しい問題も小さな問題に分解することで、問題を解くことができます。そんな分解の技術が身につくように深く関わりを持って作りました。
『大人のための高校物理復習帳』（講談社）…一般向けに日常の物理について公式を元に紐解きました。特設サイトでは実験を多数紹介しています。※増刷がかかり６刷となりました（2026/02/01）
- 『きめる!共通テスト 物理基礎 改訂版』（学研）… 高校物理の参考書です。イラストを多くしてイメージが持てるように描きました。授業についていけない、物理が苦手、そんな生徒におすすめです。特設サイトはこちら。
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