Electrostatic shielding on the issue of inner shielding and outer shielding

Well, the landlord's problem is good. I think the key lies in the concept of infinity!

In ordinary flat space, there is a major difference between the space inside and outside the ball - no matter how large the ball is, its internal space is limited, while the outer space is always infinite. A finite size is as big as it is, and it is still infinitely small compared to infinity! There is infinity in the infinite extrasphere space, but infinity is not in the finitely large intrasphere space!

In ordinary straight space, an electrostatic electric field line has the property that it can only start at a positive charge (or infinity) and only end at a negative charge (or infinity). From this feature, it can be deduced that the non-grounded (here the concept of earth is roughly equivalent to the concept of infinity, since the electric potential of both is artificially defined as 0) can only be shielded externally and not internally.

The simplest outer shield: the object of study is an uncharged, ungrounded metal spherical shell and a positively charged point charge outside the sphere. In this case, there can be no induced charge on the inner surface of the spherical shell (if there is, then its electric field lines must penetrate the metal inside or start and end on the inner surface, which contradicts the metal shell as an equipotential body.

If you think that the interior space is also infinite, then this contradiction can be avoided! ), and there must be an induced charge on the outer surface, and one side of the charge close to the point is a negative induced charge and the other side is positive. The electric field generated by these induced charges on the inside of the outer surface of the ball is exactly as large and opposite as the electric field generated by the point charges here, so that the total internal electric field is 0 everywhere.

On the outside of the sphere, the electric field lines of the negative charges in these induced charges all come from the positive point charges; Whereas the electric field lines of a positive induced charge can terminate at infinity.

If the object of study is an uncharged and ungrounded metal spherical shell and a positively charged point charge inside the sphere. In this case, there must be a negative induced charge on the inner surface of the spherical shell, so that the electric field lines emitted by the internal positive charge have an end (think that the inner space is also infinitely far away, it would be different!). Moreover, the induced charge on the inner surface cannot be positive (if there is, then its electric field lines must penetrate the metal inside or start and end on the inner surface, which contradicts the metal shell as an equipotential body); The outer surface must have a positive induced charge (because the original metal ball is not charged), and the electric field lines it emits can terminate at infinity.

However, according to the general theory of relativity, there can be unbounded but finite curved space, where there is no infinity, and the space inside and outside the large metal ball is finite and equal, and the reasoning of the first two paragraphs is not valid - either the inner and outer shields can exist at the same time, or neither can be realized. It was a strange world, but fortunately the real world was at least very close to straight space.

About "Now there will be a large metal plate between the Earth and the atmosphere along the equator." So can people in the northern hemisphere still communicate with people in the southern hemisphere? If satellite communications, optical cable communications, ionospheric communications and other communication methods are not excluded, then the answer is yes.

When I was a child, I also thought so, but these two spaces are actually different, mainly considering the problem of radius of curvature, so to speak, the radius of curvature of the outer surface is positive, the radius of curvature of the inner surface is negative, or vice versa (although there is no such thing as positive and negative), anyway, the two are not the same, at least the charge distribution is like this, because the charge will be more concentrated on the outer surface with a small radius of curvature;

For example, if a piece of metal ball has an outer surface that is concave inside, it can still be uncharged, mainly because of the size and direction of the radius of curvature.

Grounding the metal shell eliminates the electric field outside the shell.

To prove this, it is only necessary to prove that there can be no field lines in the space outside the crust.

Since the conductor shell is equipotential, the same field line cannot start at one point on the outer wall of the shell and end at another point on the outer wall.

Similarly, because the field strength at infinity is 0, the entire infinity region is an equipotential region, and the same field line cannot start at infinity and end at infinity. It can be seen that if there is an electric field outside the shell, it can only start from the outer wall of the shell and end at infinity or vice versa.

However, this is not possible when grounding, because the spherical shell potential is equal to the ground potential.

So there can be no field lines in the outer space of the shell.

I probably don't know much about your question, but I want to know what you mean by inner and outer screens?

Is there only an outer shield? My understanding is that the shield should be blocked, from the outside to the inside, and from the inside to the outside, but normally the signal is from the outside, so it is the outer shield.

Let's understand the essential reason for electrostatic shielding, electrostatic shielding is actually the use of metal balls on both sides of the internal space, with induced charges, to form an induced electric field to offset the original electric field, think about it, how to distribute the induced charge on the metal ball can not be distributed to both sides of the external space, and how can this induced electric field be formed in the external space?

Your question is only valid on a philosophical level, but it doesn't make sense physically.

I think the shielding should be blocked, from the outside to the inside, from the inside to the outside, but normally the signal is from the outside, so it is the outer shield.

Upstairs, if the iron ball is big enough, the ball wall is thick enough. I think it can also be shielded internally.

The principle of electrostatic shielding is as follows:

If a conductor is placed in an external electric field with an electric field strength of e, the free electrons in the conductor will move against the direction of the electric field under the action of the electric field force. In this way, the negative charge of the conductor is distributed on one side and the positive charge is distributed on the other, which is the phenomenon of electrostatic induction. Due to the redistribution of charges within the conductor, these charges form another electric field in the opposite direction to the external electric field, and the electric field strength is within e.

According to the principle of superposition of field strengths, the electric field strength in the conductor is equal to the superposition outside e and inside e, and the opposite electric field superposition cancels each other out, so that the total electric field strength inside the conductor is zero. When the total electric field strength inside the conductor is zero, the free electrons inside the conductor no longer move directionally.

In physics, the state in which there is no charge moving in a conductor is called electrostatic equilibrium. The internal electric field strength of a conductor in this front state in electrostatic equilibrium is zero everywhere. It can be inferred that the charge of a conductor in electrostatic equilibrium is only distributed on the outer surface of the conductor.

If this conductor is hollow, when it reaches electrostatic equilibrium, there will also be no electric field inside. In this way, the shell of the conductor will play a "protective" role on its inside, so that its interior is not affected by the external electric field, and this phenomenon is called electrostatic shielding.

The electric field strength formed by the external electrostatic charge and the induced electric charge on the outer surface of a conductor metal cavity inside the metal cavity is zero, and the electric field strength formed by the internal charge of the metal cavity and the surface charge inside the metal cavity outside the metal cavity is zero. Therefore, the metal cavity can shield the external electrostatic field, and the grounded metal cavity can shield the internal electrostatic field.

The basic principle of electrostatic shielding: if the conductor is placed in an external electric field with an electric field collapse strength of e, the free electrons in the conductor will move in the direction of the opposite electric field under the action of the electric field strength.

The negative charge of the conductor is distributed on one side and the positive charge is distributed on the other side, which is the phenomenon of electrostatic induction by Lu Gaichi. Due to the redistribution of the load inside the conductor, these charges form another electric field in the opposite direction to the external electric field, and the strength of the electric field is within e. According to the principle of superposition of field strengths, the intensity is the superposition of the electric field in the conductor equal to e and e.

When the total strength of the electric field inside the conductor is zero, the free electrons in the conductor no longer move. In physics, the state in which there is no charge moving in a conductor is called electrostatic equilibrium. In a conductor in static equilibrium, the strength of the internal electric field is zero.

It can be inferred that a conductor in electrostatic equilibrium is only distributed on the outer surface of the conductor.

If this conductor is hollow, when it reaches electrostatic equilibrium, there will be no electric field inside. In this way, the outer conductor cover will "protect" its interior, making it immune from external electric fields. This phenomenon is called electrostatic shielding.

Meaning of electrostatic shielding

1. Practical significance: The shielding makes the instrument or working environment in the metal conductor shell not affected by the external electric field, nor does it have an impact on the external electric field. In order to avoid interference, some electronic devices or measuring equipment must be shielded electrostatically, such as a grounded metal cover or a dense metal mesh cover on the indoor high-voltage equipment cover, and a metal tube shell for electronic tubes.

2. The power transformer of full-wave rectification or bridge rectification should wrap a metal sheet or a layer of enameled wire between the primary winding and the secondary winding and grounding it to achieve shielding effect. In high-voltage live work, workers wear pressure equalizing clothing woven with metal wire or conductive fibers, which can shield and protect the human body.

3. In the electrostatic real early Li test, there is a vertical electric field of about 100V m near the earth. To rule out the effect of this electric field on the electrons, to study the movement of electrons only under the action of gravity, it is necessary to have EE<10-10V m, which is an "electrostatic vacuum" with almost no electrostatic field, which can only be achieved by electrostatic shielding of the cavity pumped into the vacuum. In fact, electrostatic shielding achieved by a closed conductor cavity is very effective.

1. Use a metal shell or metal mesh to enclose an area, so that the area is no longer affected by the external electric field, this phenomenon is called electrostatic shielding.

2. Reason: The charge of the charged object in the metal shell causes the charge of the same size and opposite properties to accumulate on the inside of the shell, and the charge with the same nature is gathered outside the shell, for the metal shell, only the charge distribution changes, and the net charge is still 0. Therefore, the charge of the charged body in the shell only has an effect within the scope of the shell, and for the external environment, its electricity is equivalent to being shielded.

To put it simply, the conductor generates an induced electric field that is opposite to the external electric field, so it is electrostatically shielded.