Electrostatic Shielding

What is electrostatic shielding?

Electrostatic shielding is defined as a phenomenon that is seen when a Faraday cage is used to block the effects of an electric field. The effects of external fields on the internal contents are blocked using the cage.

Electrostatic shielding applications

  • During the lightning thunderstorm, it is advised to stay inside the car and not under trees or in the open ground because the outer metallic body of the car acts as an electromagnetic shield from the lightning.
  • In coaxial cable, the central conductor is protected by electrostatic shield by connecting the outer conductor to the ground.

What is Faraday cage?

The Faraday cage is an enclosure used to block the external electric fields in conductive materials. It is also known as Faraday shield.

Michael Faraday in the year 1800 invented Faraday’s cage. He found that when the metal cage which acts as an electrical conductor was charged, the charges appeared only on the surface with no effect on the interiors. When this was conducted on a large scale, he lined a room in a metal foil allowing high-voltage discharges from an electrostatic generator. He used a device to detect the electric charges called electroscope to prove his hypothesis that the outer surface of the metal foil was conducted by the current whereas the interior of the room was devoid of electric charges.

How does Faraday cage work?

Faraday cage has a cage-like appearance made of fine metal mesh and chain-like fences which vary in sizes and designs. The cage can hold the electrostatic charges and electromagnetic fields such that they get distributed throughout the exterior of the material it is used on. The distribution of charges on the exterior surface happens in such a way that the charges cancel with the charges in the interior.

Faraday cage applications

  • MRI scanning rooms: The rooms are built in such a manner that they prevent the mixing of the external radio frequency signals with the data from the MRI machine.
  • Microwave ovens: The mechanism used is based on Faraday cage such that the electromagnetic energy within the oven is contained and the exterior is a shield from radiation.
  • They find application in analytical chemistry to reduce noise while making sensitive measurements.

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Practise This Question

A block of mass 'M' is placed on the top of a bigger inclined plane of mass '10M' as shown in figure. All the surfaces are frictionless. The system is released from rest. Find the distance moved by the bigger block at the instant the smaller block reaches the ground.

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