When the metal ball of a positively charged electroscope is grounded, the metal foil closes

Electrons are negatively charged, and positively charged metal foils are positively pointed because of the lack of electrons. And the earth has an extra negative charge, so when the two come into contact, it is the electrons of the earth that are transferred to the metal foil, causing the metal foil to close.

a. The transfer of electrons to the earth in the metal foil --- wrong. Because when the electroscope is positively charged, it means that the electroscope lacks electronics. (It can also be said that the electroscope is positively charged because the electroscope lacks electrons) (a substance is made up of molecules (atoms), and atoms are composed of nuclei (positively charged) and extranuclear electrons (negatively charged), and in the process of electrostatic testing, an object can gain electrons or lose electrons outside the nucleus of the outermost layer of the atom (the nucleus cannot move).

When an object gains electrons, the object becomes negatively charged; When an object loses electrons, the object becomes positively charged);

b. The transfer of protons to the earth in the metal foil --- wrong. Because protons are part of the nucleus, the nucleus does not move at this time;

c. The transfer of atoms from the earth to the metal foil --- wrong. Because the atom itself is electrically neutral, even if an atom is transferred to the electroscope, it will not neutralize the classics on the electroscope;

d. Electrons on the ground are transferred to --- pairs on the metal foil. Because the electroscope lacks electrons, and the earth is defined as the carrier through which free electrons can flow in and out, when the electroscope lacks electrons, there are electrons on the ground that are transferred to the metal foil, neutralizing the static electricity on the gold foil, and the metal foil is closed.

Explained in terms of electron transfer:

Option B: A ball is negatively charged, when it is close to ball B, the electrons (negatively charged) at the near end of ball B are transferred to the distal end under the action of charge repulsion, that is, the electrons are "moved down", and the metal foil at the distal end is originally positively charged, and part of it is neutralized by the electrons that move downward, and the positive charge is reduced, so that the opening angle of the two gold foils is reduced.

Option A: Ball A is not charged, when it is close to ball B, because ball B is positively charged, so the electrons on ball A are transferred to the end face of ball B under the action of charge attraction, as if ball A is negatively charged, and the explanation of option B is the same: on ball B, the electrons at the near end (negatively charged) are transferred to the far end under the action of charge repulsion, that is, the electrons are "moved down", and the metal foil at the far end is originally positively charged, and part of it is neutralized by the electrons that are moved downward, and the positive charge is reduced, so that the opening angle of the two gold foils is reduced.

The meaning of "electroscope positive" is actually more positive than negative charge on the electroscope, and this sentence is true, that is, some electrons on the electroscope have been transferred to other objects.

Also, you said this question very rigorously, "only close but not touch", if it is contact, then the answer is: ABC three.

The electroscope was originally positively charged, and in order to reduce the opening angle, the electrons at B should be transferred to the metal foil, and according to the interaction between charges, the A ball may be negatively charged;

If the A-ball is not charged, the left side of the A-ball will also be negatively charged due to induction, so the same effect will be produced;

Therefore, the A-ball can be negatively charged or uncharged;

Therefore, b

Because the metal ball of the electroscope is positively charged, the metal foil of the electroscope is closed first, indicating that the object is negatively charged, and the positive charge of the electroscope is neutralized with the negative charge of the object, and then it is opened because the negative charge of the object is redundant to the electroscope, and the metal foil of the electroscope is opened because of the same charge

So choose A

The electroscope was originally positively charged, and in order to reduce the opening angle, the electrons at B should be transferred to the metal foil, and according to the interaction between charges, the A ball may be negatively charged;

If the A-ball is not charged, the left side of the A-ball will also be negatively charged due to induction, so the same effect will be produced;

Therefore, the A-ball can be negatively charged or uncharged;

Therefore, b

Answer D Comment: The charged body in the question is through an electroscope.

Verify that it is charged, but can not determine what kind of electricity it originally carried, it may be positively charged, or it may be negatively charged, if it turns out that it is positively charged, it lacks electrons, then it is in contact with the electroscope, the electrons of the metal foil will be transferred to the charged body through the metal ball of the electroscope, so that the charged body gets electrons, the metal foil loses its electrons and is positively charged, and the metal box is open If the charged body is negatively charged, it has excess electrons, A part of the excess electron is transferred to the metal foil through the metal ball of the electroscope, and the metal foil gets the electronic metal foil open Consider two cases Correctly answer the rent case option d

It has been found that there are only two kinds of electric charges in nature The essence of triboelectric electricity is the transfer of electrons When the charged body touches the metal ball of the electroscope, the two metal foils of the electroscope open due to the mutual repulsion of the same charge

So the answer is: two; transfer of electrons; Homogeneous

Answer A analysis: the foil should not be charged when closed, and the neutralization of positive and negative charges should occur in the process of opening and closing the foil from the original loss to the closing The electroscope was originally positively charged, and the object must be negatively charged in order to neutralize the positive charge of the curved electroscope The two foils of the electroscope are closed and opened again because the number of negative charges brought by the object is greater than the number of positive charges carried by the electroscope, and the negative charge is returned and there is a surplus after neutralization, so that the foil is reopened with a negative charge

When the metal ball is grounded, the metal foil of the electroscope is positively charged due to the attraction of different charges, so the free electrons on the ground will be transferred to the metal foil through the metal conductor to neutralize the positive charge on the electroscope

Therefore, choose D