Faraday cage


When an electrical charge accumulates on the outside of a metal box, the electrons in the metal that make it up move to cancel out any charge on the inside. This is precisely what Michael Faraday discovered with the Faraday  cage , that an electrical charge cannot be passed into a metal box or covered with an electrical mesh .


What is the Faraday cage?

The Faraday cage, made in 1836 by the British Michael Faraday , is a rectangular or square container where, being formed by a conductive material , such as aluminum or metal, it causes the concentration of external electric fields to be zero, and in turn, Inside, a conductor is generated in null equilibrium , adapting so that one side of the box remains with the negative charge, and the other side remains without electrons, producing only a positive charge.

  • What is the Faraday cage?
  • Functioning
  • Applications and uses of a Faraday cage
  • How to make a Faraday cage
  • History of the Faraday cage

What is the Faraday cage?

The Faraday cage consists of a container made of a conductive material , such as a wire mesh or several metal plates, which means that the concentration of electrostatic fields generates that in its interior, electrical charges do not occur. , serving as protection or electrical shielding and generating that all its negative charges reside on only one side of the cage and do not mix with the positive charges.


The isolation or impediment of penetration of electric charges, known as the Faraday effect, radiates in a conductor of null equilibrium which cancels the external fields and is polarized in such a way that it remains only with positive charges in the direction in which the electromagnetic field goes, and the electrons (negative charge), in the opposite direction. Producing that the conductor when polarized generates an electric field where the charges would be zero.


The proper functioning of a Faraday cage is based on the properties found in the electrostatic conductor , since when the metal or aluminum box is placed in the presence of an external electric field, the positive charges are trapped in the network; the electrons, in turn, move in the opposite direction of the electric field. Although the total charge of the conductor is zero, one side of the box remains with an excess of negative charge, generating in turn that the other side runs out of electrons, producing only positive charge. The metal box (or in its defect, aluminum), is able to repel the positive charges found in their original position, while the electrons (negatively charged),they settle in the opposite direction to the generated magnetic field (it repels it), thus forming one side of the container with excess negative charge, while the other side remains uncharged .

Its operation in everyday life lies, for example, in the use of microwaves to heat food . In turn, inventions such as the automobile, which is capable of protecting its occupants from an electrical shock produced by lightning; as electronic devices , such as mobile phones, audio devices , among others; Since these employ the Faraday cage principle in order to avoid interference and noise between other speakers and microphones. 

Applications and uses of a Faraday cage

The application and usefulness of a Faraday cage is still used in everyday devices, where not only Faraday revolutionizes aspects of science but also daily life in general , such as:

  • Present safety against lightning or lightning: As much as automobiles and airplanes, it is subjected to the weather of a storm with electrical charge , these means of transport must protect its crew members, for this reason, its structure is conditioned as a cage of Faraday, providing security inside.
  • The need for protective suits : Both as technicians and specialists in working with high voltage materials and electricity charges, they are exposed to being affected by the environment in which they work, therefore, protective suits are made, which they act like Faraday cages by repelling high voltage loads, protecting the user from receiving an electrical shock.
  • Electric motors: The Faraday motor prototype served as a starting point for electric motors that can be seen in later years, the one proposed by Faraday was primitive but at the same time complex, which makes motors known as today .
  • Insulators and inhibitors: From Faraday’s theories it is observed that some places may require a certain metallic structure which in turn creates a kind of Faraday cage, this in everyday life causes some sites to suffer from poor coverage given that waves are prevented from leaving the building.

How to make a Faraday cage

The procedure for the realization of a Faraday cage requires the use of materials such as: a container or container of a conductive material, for example, a wire or metal mesh, which will provide that external electric fields are enclosed. Heavy duty scissors, wood slats, stapler and staples.


  • Continue making a rectangle with the wire or metal mesh, it can be more or less about 8 x 16 inches, cutting this rectangle with the working scissors.
  • The wooden slats of about 8 inches in length and about 5 slats are now measured.
  • The already cut rectangle of the mesh is extended, taking care that it is flat.
  • The wooden slats are then stapled to the rectangular mesh with the stapler.
  • The first slat is located at the end of the mesh, the second at 5.5 inches from the first, the third at 2.5 inches from this second, the third again at 5.5 inches from the latter, and the fifth slat being to the end of the mesh.
  • The wooden slats serve a clamping function, so the mesh must be folded in each strip to form a rectangular box that will be the Faraday cage.

History of the Faraday cage

At the beginning of 1831 , the British Michael Faraday with studies in both physics and chemistry began to experiment, reaching clues that led him to the discovery of electromagnetic induction ; and then focus on working static electricity, where he manages to realize the excess load that was in a single conductor, which was only on the outside, did not have any influence. So the scientist wanted to prove to the world what he had discovered. To do this, he began to condition a room with aluminum foil so that the high voltage discharges produced from an electrostatic generator would resonate outside the room. Faraday proposes the use of the electroscope in order to show that there was no electrical charge present inside the room but only outside.

Faraday succeeds in demonstrating this by conducting an experiment in which he used an ice bucket and a metal sphere , thus lowering the statically charged sphere into a metal bucket on a wooden chair that served as insulation for the bucket from the floor. When this sphere managed to go down and enter the bucket without touching it, the charges found on the surface of the bucket were redistributed from electrostatic induction, giving rise to the principle known as the Faraday cage .

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