Scientists Say: Faraday cage

This is a fence that keeps electricity out

These girls are standing inside a Faraday cage. They are protected from the electricity zapping on the outside.

Antoine Taveneaux/Wikimedia Commons (CC BY-SA 3.0); adapted by L. Steenblik Hwang

Faraday cage (noun, “FARE-ah-day cage”)

This is a box made of a material that blocks electromagnetic fields. A metal that conducts electricity, such as copper is used to construct the cage. When electricity — or certain types of electromagnetic radiation — hits a Faraday cage, the metal distributes the charge around the box. That protects whatever (or whoever) is inside.

Scientists build Faraday cages to protect very sensitive experiments. But Faraday cages don’t have to be cages or boxes. Some people line bags or wallets with metal mesh to make a small Faraday cage to protect their smartphone or laptop. And an elevator can sometimes act like a Faraday cage. That’s why your phone might lose signal inside.

The Faraday cage is named after its inventor, Michael Faraday. He made the first Faraday cage in 1836. He built a large box and lined it with wire mesh. To test his invention, Faraday zapped it from the outside with electricity while he stood inside.

In a sentence

City birds get confused by electromagnetic fields — unless they’re perched inside a Faraday cage.

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Bethany is the staff writer at Science News for Students. She has a Ph.D. in physiology and pharmacology from Wake Forest University School of Medicine.