Electrostatic Shielding

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What is Electrostatic?

Electrostatic means Static electricity.


We might have seen a chain hanging down the ground of the truck; it’s because trucks get charged on getting friction between them and the air rushing past them. This charge being large can even produce a spark, which can be dangerous in the case of a petrol tanker.


The charge produced leaks to the ground through the chain hanging at the back of the truck. Since the charge is static and can not pass on its own, that’s why they are called static charges or electrostatics. This chain acts as an electrostatic shielding for a petrol tanker.


Note: There are some objects/regions, which are sensitive and are shielded with a hollow conductor around it to protect from the intense electric fields via electrostatic shielding.


In this article, we are going to practically understand what is electrostatic shielding and its application?

What is Electrostatic Shielding?

Electrostatic shielding is a method of shielding or protecting a particular region or space or any sensitive building/instrument from the effect of the external field produced by an electric charge.


For example, an instrument used to measure high voltage viz: CRO is kept inside a hollow conductor or cage called the Faraday’s cage.

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According to the practical demonstration of electrostatic shielding, the fact of keeping this instrument inside the conductor is, there is no electric charge inside a closed conductor when there is no charge inside it.  


Michael Faraday took a high-voltage generator, prepared a large wired cage supported on insulators, and sat inside the cage with gold leaf electroscopes, which were electric field detectors. 

                   

When this cage was charged with an induction machine, Faraday observed no deflection in electroscopes. Also, he could sit safely and comfortably inside the cage.


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So, hollow conductors work as a protective layer for humans and devices from mighty electric fields. These hollow conductors or Faraday cages are used to obstruct electric charges from setting at one place by establishing an electric field beyond their immediate vicinity and surround the charges with a Faraday cage and connect this cage to the earth. 

Do You Know Why We Earthed the Cage?

It’s because, if the cage is not earthed or grounded, electrons will distribute in a manner that the interior wall of the cage would acquire a charge opposite to that internal charge. This, in turn, will leave the exterior wall opposite charge to that of the internal.                                             

Now, what happens next is, after grounding the cage, the excessive charge induced around it leaks to the earth, and there is no external field. So this was the case when we wanted to release the charge. However, if we wish to seal something inside the cage, it should not be earthed. 


What is Electrostatic Shielding in Physics?

Now, we will focus on how electrical instruments are sensitive and why they need to be shielded?

The instrument that is to be protected from an external electric field is placed inside the conducting box (made of copper), and place the Van de Graff generator nearby this box,

 as shown below:

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Now, the electric field generated around the generator drifts electrons towards this conducting body from one side to the other, thus, creating a net positive charge on the other side of the box. Further, this charge distribution creates an electric field.


Now, according to Gauss law, the net electric field at every point inside the conductor is zero. So, the question arises, does the conductor protect the instrument from an external electric field? 


Yes, it does. It’s because when an electric field operates on a Faraday cage (box made of copper), the charges with a cage rearrange themselves to directly counterbalance the field, and hence, the shield (protect) the internal of the cage from the external electric field.                                               

Applications of Electrostatic Shielding

Electrostatic Shielding meaning is to make a region free from dangers viz: external electric field. 

Now, let’s look at the electrostatic shielding applications:

  • Electrostatic Shielding in Cars: 

It is safe to sit inside the car during a lightning thunderstorm because the metallic body of the car works as an electrostatic shield.

  • The concept of electrostatic shielding is used in wires carrying audio signals. to protect them from external interference viz: electric field produced because of the atmospheric electricity or electric sparks.

  • Electrocution:

To protect themselves from being killed by an electric shock or electrocution, linemen wear suits that are made of Faraday cages.

  • Elevators in buildings act as an electrostatic shield as the cell phone, radio, and audio signals get shielded.

  • The coaxial cables in the outer conductor are connected to the earth to provide electrostatic shielding to the signals that are transferred by the central conductor.

FAQ (Frequently Asked Questions)

Question 1: Why is the Electric Field inside a Cavity Zero? State Any One Application of Electrostatic Shielding.

Answer: When any current-carrying conductor is placed inside the electric field Ec, the electrons inside it acquire motion in a direction opposite to that of an electric field. Also, the redistribution of charges generates its own electric field Ep. Hence, the net electric field, i.e., Ec - Ep becomes zero. That’s why the electric field inside the cavity is zero.

Question 2: What is an Electrostatic Equilibrium?

Answer: Electrostatic equilibrium is a condition built by charged conductors in which the excess charge distance by themselves to overcome the repulsive forces.

Question 3: State One Limitation of Faraday’s Cage.

Answer: Faraday cages cannot block static and slowly changing magnetic fields (as that of the planet Earth). However, they can shield the interior from external magnetic radiation provided that the mesh is smaller than the radiation’s wavelength and that the shield is adequately thick.

Question 4: How does a Microwave Oven act as an Electrostatic Shield?

Answer: The phenomenon used here is based on Faraday’s cage. A microwave oven uses a Faraday cage, which can partially be observed covering the transparent window to seal the electromagnetic energy within itself and to shield the exterior from harmful radiation.