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Michael Faraday was one of the great scientists in history. Some historians of science refer to him as the greatest experimentalist in the history of science. It was largely due to his efforts that electricity became a viable technology.
He developed the first dynamo in the form of a copper disk rotated between the poles of a permanent magnet, the precursor of modern dynamos and generators. From his discovery of electromagnetic induction (1831) stemmed a vast development of electrical machinery for industry. In 1825, Faraday discovered the compound benzene. In addition to other contributions he did research on electrolysis, formulating its two laws. He laid the foundations of the classical field theory, later was fully developed by J. C. Maxwell.
In his work on static electricity, Faraday demonstrated that the charge only resided on the exterior of a charged conductor, and exterior charge had no influence on anything enclosed within a conductor. This is because the exterior charges redistribute such that the interior fields due to them cancel.
Another explanation for the Faraday cage effect can be derived from Gauss's law that states that if there is no charge in a closed surface then the net flow of electric field from the surface must be zero.
For a better understanding of how a Faraday cage works try this demo.
To demonstrate his ideas, Faraday built in 1836 a room (the Faraday cage), coated with metal foil, and allowed high-voltage discharges from an electrostatic generator to strike the outside of the room. He used an electroscope to show that there was no excess electric charge on the inside of the room's walls and volume.
The Faraday cage can be used to prevent the passage of electromagnetic waves and electric fields, either containing them in or excluding them from its interior space.
This shielding effect is used to to protect electronic equipment from lightning strikes and other electrostatic discharges, for RF (radio frequency) shielding and for shielded telecommunication cables.
Practical Faraday cages can be made of a conducting mesh instead of a solid conductor. However, this reduces the cage's effectiveness as an RF shield.
Some real-world structures, such as automobiles, behave approximately like a Faraday cage. For example: If lightning hits near a car, it does not affect the people sitting in the car.
Some traditional architectural materials act as Faraday shields in practice. These include plaster with wire mesh, and rebar concrete. These will impact the use of cordless phones and wireless networks inside buildings and houses.
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Preparation:
- Cut two aluminium ribbons of 1 cm large and long enough to wrap the electroscope from the bottom to the lid.
- Lay them on the table in the form of a Greek cross.
- Place the electroscope on the middle of the cross and fold the ribbons along the container up to the lid. The metal ribbons surrounding the electroscope constitute an electrostatic screen.
Stage a:
Charge a straw and bring it close to the plate of the electroscope: the leaves diverge.
Stage b:
Cap the plate of the electroscope with the metallic cap and bring the charged straw close to the plate again: the leaves remain close together.
This experiment proves that external charges have not any effect on the shielded (Faraday caged) electroscope.
Another quick experiment:
Place a radio inside a Faraday cage and it becomes silent.
More Faraday Cage Experiments and Background
Faraday’s "Ice Pail" Experiment - The Open Door Web Site
Faraday's Ice Pail Experiment - Catharine H. Colwell
Faraday's Ice Pail - J. B. Calvert
Easy Electrostatics Experiments - Michel Maussion, University of Nantes, France
Faraday Cage - Ken Skeldon
Faraday cage - Holland Shielding Systems
Faraday Cages in Health Care
EMI Shielding EMC/RFI Solutions - Holland Shielding Systems
Faraday Cages, TEMPEST equipment - Holland Shielding Systems
Faraday Cage Demo - The Fajans Group Home Page
Gauss's Law - G. Borrisov
More electricity & magnetism science fair projects and experiments
Electricity & Magnetism Science Fair Projects and Experiments
Michael Faraday biographies and general resources:
Michael Faraday - The Royal Institution of Great Britain
Michael Faraday - MacTutor
Michael Faraday - BBC
Michael Faraday - Eric W. Weisstein
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