[Physics Class Notes] on Electrostatic Shielding Pdf for Exam

Electrostatic means Static electricity.

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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 them to protect from the intense electric fields via electrostatic shielding.

 

In this article, we are going to practically understand what electrostatic shielding is 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.

 

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.

 

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 surrounding the charges with a Faraday cage and connecting 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 placed the Van de Graff generator nearby this box.

 

ow, 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 (protects) the internal of the cage from the external electric field.                                               

 

Applications of Electrostatic Shielding

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

 

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

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.

 

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.

 

Faraday cage

The Faraday cage, also known as the Faraday shield, is a type of enclosure created to keep the electric field completely out of conductive materials. It was named after its inventor Michael Faraday, who designed this enclosure in the year 1800. One day, he discovered that when a metal cage, which works like an electric conductor, is charged, then the charge gets concentrated on the surface of the metal and the interiors of that cage get devoid of any kind of charge, it does not have any effect on the interior of the metal cage. 

 

On a larger scale, he wrapped metal foil around his room and permitted a high-voltage charge into that metal foil with the help of an electrostatic generator. And Now to validate his hypothesis, he used an electric device by the name of electroscope to map the entire room and found that his hypothesis was correct, that the only charge present there was concentrated in the metal foil and the interiors of the room were devoid of any charge.

 

Application of Faraday cage

Some of the major real-life applications of Faraday’s cage are as follows – 

• MRI scanning rooms: The rooms are built especially to prevent the external radio frequency that can get mixed with the MRI data. In this case, the room acts as a faraday’s cage

• Microwave ovens: The mechanism used in the microwave ovens also utilised the same concept of Faraday’s cage but not in a true sense.

• Faraday’s cage is widely used in analytical chemistry to perform extremely delicate tasks, so get data with better accuracy.

 

Conclusion

Getting a complete insight about Electrostatic Shielding and its applications will certainly help in getting an idea how it works.