Electrostatic Induction
Electrostatic induction
In the last chapter it was shown that a force acts between charged bodies, the Coulomb force, which makes bodies attract or repel each other based on their charge. In experiments it was found that this force also acts to some extent between a charged body and an uncharged body. This is made possible by a charge separation in an uncharged body, thereby forming an electric field in it.
As explained in the section conductor / insulator negative charges (electrons) can move almost freely in conductive bodies (e.g. metals), while the positively-charged atomic nuclei are firmly rooted in the atomic structure.
If a charged body as brought near to a metal ball, a force acts between the charged body and the charges in the metal, making the negative charges move in the metal. As such on the side of the sphere on which the electrons are located there is negative charge excess and on the opposite side there is a negative charge deficiency or positive charge excess. That's why two poles are formed and thus an electric field is created in the metal ball.
Coulomb force
We now repeat the experiment from the last chapter. But this time with a charged and an uncharged metal sphere.
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Man beobachtet, dass sich die beiden Kugeln anziehen. Dies liegt daran, dass sich durch Influenz in der ungeladenen Metallkugel ein elektrische Feld aufgebaut hat. Nun wirkt die Coulombkraft zwischen den Körpern. We observe that the two balls attract each other. This is because an electric field has been created in the uncharged metal sphere by electrostatic induction. As such the Coulomb force acts between the bodies.
Electric polarization
In insulators, the electrons are bound to the nucleus of the atoms, which means they can not move freely in the insulator. Usually, the center of charge of the electrons and the center of charge of the nuclues are both in the center of the atom.
Wird nun ein geladener Körper in die Nähe eines Isolator gebracht, so verschieben sich die Elektronenhülle und der Kern leicht, sodass die Ladungsschwerpunkte nicht mehr aufeinander liegen. Es entstehen kleinste elektrische Dipole und die Oberfläche des Isolators lädt sich auf. When a charged body is brought close to an insulator the electron shell and the core move slightly, such that the charge centers are no longer together. As such very small electric dipoles are created and the surface of the insulator charges.
Sources
- Wikipedia: Article about "Electrostatic induction"
- Wikipedia: Article about "Polarization density"
- Deutsche Version: Artikel über "Influenz / dielektrische Polarisation"