What is a Faraday Cage? - Definition & Material

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  • 0:03 Definition of a Faraday Cage
  • 1:10 Faraday Cage Building…
  • 1:50 How Faraday Cages Work
  • 2:18 Faraday Cage Limitations
  • 2:47 Faraday Cage Examples
  • 3:45 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

Science is pretty amazing as you can see with experiments involving the Faraday cage. Read this lesson to learn how Faraday cages work and exist in everyday life.

Definition of Faraday Cage

Have you ever been on a road trip and driven through a thunderstorm? What do you think would happen if your car got struck by lightning? Do you think you would be electrocuted? Lucky for you, your car is a safe place to be, as your car acts like a Faraday cage.

A Faraday cage is a conductive cage that protects the inside from external electric fields and external electromagnetic radiation. Faraday cages are also called Faraday shields, RF cages, or EMF cages. The Faraday cage is actually very popular and is in use in our everyday lives.

The Faraday cage is named after Michael Faraday, who built one in 1836 and observed that when electrical charges strike the outside of the cage, it does not affect the inside. He wrapped a room in metal foil, placed an electroscope inside the room that would measure the presence of any electric charges, and then applied electrical charges to the outside of the room. He observed that the electroscope inside the room always read 0, no matter what happened outside the room.

How is this done, you may ask? Well, let's take a closer look.

Faraday Cage Building Materials

It all begins with the materials used to build a Faraday cage. It actually isn't hard to build one yourself. In fact, you probably have all the materials you need in your kitchen. The only material you need is this: conductive material.

A conductive material is one that lets electricity pass through. Metals are the most common conductive material in use today. Other examples are water and the human body. The opposite of a conductor is an insulator, materials such as rubber, wood, glass, or plastic. These materials do not allow electricity to pass through. But how does building a cage out of conductive material protect what's inside from electricity?

This bird cage is surrounded by metal, making it a Faraday cage as well
faraday cage

How Faraday Cages Work

When a Faraday cage is exposed to an external electrical force, the electrons of the conductive material of the cage respond and move in such a way so as to cancel out the external electrical force. The Faraday cage ends up producing its own electrical force that's exactly opposite the electrical force it's being exposed to. This equal and opposite force cancels the external force. What you get inside the cage is a completely neutral electrical environment.

Faraday Cage Limitations

There are limitations to the Faraday cage, however. They don't block magnetic fields, so the earth's magnetic field will make its way through. Also, the type of conductive material used and how it's constructed also determines the response of the electrical force. Meshes, for example, don't protect as well as a solid sheet of metal. Different types of metal also have different conductivities. Copper, for example, has higher conductivity and makes for a better Faraday cage as it responds to more electrical forces.

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