Why do charged and neutral objects attract

Electric charge¶

All substances that we know are made up of atoms. Each of these atoms in turn consists of even smaller components. The positively charged protons of the atomic nucleus and the negatively charged electrons of the atomic shell are of particular importance for electricity and magnetism.

In simplified terms, electrons can be understood as small particles that orbit the atomic nucleus on spherical orbits, similar to how the planets in our universe orbit the sun. Since the electrons are very tightly bound to the atomic nucleus on the inner paths (“shells”), they are out of the question as charge carriers for the electric current. The electrical properties of a substance are therefore (almost) exclusively influenced by those electrons that are on the outermost switch ("valence electrons").

In general, the following applies to every chemical element:

  • In an atom, the number of protons is equal to the number of electrons.

    While the protons are firmly anchored in the atomic nucleus, the electrons are more or less strongly bound depending on the type of substance.

    Electrons can also leave an atom completely. A positively charged ion (“cation”) then remains as the “core of the atom”. However, the substance remains unchanged - only the number of protons in the atomic nucleus is characteristic of each chemical element.

  • Protons and electrons are equally charged.

    Since every atom has the same number of positive and negative charge carriers, its total charge, i.e. the sum of all charges, is zero. Seen from the outside, an atom therefore appears to be an electrically neutral particle.

All electrical charges occurring in reality are made up of the charges of the electrons and protons.

Unit:

One has as a unit of electrical charge set an amount of charge that is as large as the electrical charge of Electrons. This unit becomes the coulomb called.

By means of this definition one can also say that an electron has a charge of owns. This charge is also the smallest charge that can occur freely in nature - it is therefore also called "elementary charge" .

Charge separation¶

Under certain conditions, electrons can be separated from one body and additionally taken up by another body. Through such processes, bodies are electrically charged. The following always applies:

  • A body is electrically neutral when there are equal numbers of positive and negative charges.
  • A body is electrically positively charged () when there is a shortage of electrons.
  • A body is electrically negatively charged () when there is an excess of electrons.

The total amount of charge is retained with each charge separation. In solids, only electrons can be transferred from one body to another through friction. The positive charge carriers are also mobile in liquids and gases.

Example:

  • If you rub a piece of hard rubber (filler, comb, etc.) on a piece of wool (scarf, sweater, etc.), electrons are transferred from the wool to the hard rubber. If you separate the two from each other, the hard rubber remains negatively charged due to the additional electrons. Correspondingly, atoms with missing electrons remain in the wool; the wool is positively charged because of these missing electrons.

Whether a body is positively or negatively charged by a friction process depends on the type of substances involved. If you rub two bodies against each other, the substance closer to the plus sign of the so-called “contact electrical voltage series” releases electrons and becomes electrically positive. The substance closer to the minus sign absorbs electrons and becomes electrically negative.

Tape generators

With a belt generator, a charge separation through friction can be repeated to a considerable extent and as often as required. To do this, an elastic rubber band is driven with a crank or an electric motor:

  • The belt brushes against two metal brushes, releasing electrons to the lower brush due to friction. The stripped electrons flow through a line to the small metal ball and collect there. The elastic then charges itself positively.
  • On the upper brush, the positively charged rubber band attracts the electrons in the environment. A few electrons flow from the large metal ball to the brush and discharge the rubber band. The large metal ball is positively charged.

During continuous operation, electrical voltages can build up between the metal balls of the belt generator so high that small flashes can occur: electrons then “jump” in a fraction of a second and with a bright glow from the small, electrically negative ball to the large, electrically positively charged ball . The charge is equalized and both balls are discharged.

Charge balancing and charge verification¶

If a charged body is connected to the ground via a metal wire or a similar conductive contact, a discharge occurs. This process is called "grounding".

  • If a negatively charged body is grounded, excess electrons can flow away from the body into the ground. The electrical voltage is reduced in the process.
  • If a positively charged body is earthed, electrons flow from the earth to the body and compensate for the lack of electrons there.

Since the earth has a gigantic supply of easily mobile electrons and thus every charge difference is immediately balanced out, an electrical charge on the earth is immeasurably small, even when it comes into contact with larger amounts of charge. The earth can therefore always be regarded as electrically neutral. [1]

Charges can be proven experimentally, for example, on the basis of the forces that act between charged bodies:

  • Bodies charged in the same way (plus and plus or minus and minus) repel each other.
  • Different charged bodies (plus and minus) attract each other.

The more electrically charged two bodies, the stronger the forces that act between them. The electrostatic force acting between two charged bodies can be quantitatively determined by Coulomb's law, which is described in more detail in the section Electric fields.

Electroscopes

An electroscope consists of a (usually bent) metal rod to which a pointer is attached so that it can be easily rotated. The metal rod has a contact surface at the upper end and is insulated by a plastic holder. The rotating pointer is a little heavier at the bottom, so that it is aligned vertically in its basic position.

  • If you touch the contact surface of the electroscope with a negative charged rod, the freely moving electrons with their negative electrical charges spread along the metal rod. Stick and pointer are charged in the same way and repel each other. The stronger the charge, the stronger the pointer deflection.
  • If you come closer to the contact surface of the electroscope positive charged rod, the freely movable electrons of the metal rod are attracted to the positively charged rod. In the lower area of ​​the electroscope, the firmly anchored, positively charged atomic cores remain. The stick and pointer are charged in the same way and repel each other.
  • If you touch a negatively charged electroscope with a positively charged or earthed body, it will be discharged again. (A positively charged electroscope can be discharged accordingly by touching a negatively charged or earthed body.)

With an electroscope you can measure the amount of an electrical charge, but not whether it is positive or negative.

Glow lamps

A glow lamp consists of a glass bulb in which two metal wires are fused in such a way that they are close to one another, but not touching one another. The glass bulb is filled with a gas, usually neon, under low pressure.

Glow lamps are used to verify the charge at high electrical voltages (at least 180 volts). If you touch a negatively charged body with a conductive contact of the glow lamp, for example the small metal ball of a charged ribbon generator, the area around the metal wire in the glow lamp lights up.

An electroscope or a glow lamp can only be used to detect if a body is electrically charged or not. A quantitative statement how strong a body is electrically charged, however, is not possible with these two aids.

For better handling, glow lamps - similar to batteries - are often provided with a socket. In this way, a glow lamp can be built into a circuit with suitable plugs and serve as a "control lamp" for an applied mains voltage.


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