Electric charge . Electromagnetic forces are responsible for the structure of atoms and their bonding in molecules and solids. Many material properties are electromagnetic in nature, such as the elasticity of solids and the surface tension of liquids. Spring force, friction, and normal force originate from the electromagnetic force between atoms. Examples of electromagnetism include the force between electric charges, such as that between the electron and the nucleus in an atom .
Summary
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- 1 In nature
- 2 conductors and insulators
- 3 Example 1.
- 4 Example 2.
- 5 Source
In nature
On a broader scale, the phenomenon of lightning is known to all . This phenomenon highlights the large amount of electrical charge that is stored in objects found in nature.
The electrical neutrality of most objects in the visible and tangible world hides the contents of the enormous amount of positive and negative electrical charge that, for the most part, cancel each other out in their external effects. Only when this electrical balance is disturbed does nature reveal the effects of an uncompensated positive or negative charge. When a body is said to be ¨charged¨ it means that it has a charge imbalance, even though the net charge generally represents only a very small total positive or negative fraction contained in the body.
The charged bodies exert force on each other. To demonstrate this, a glass rod is loaded by rubbing it with silk. In the rubbing process a very small amount of charge is transferred from one body to another, thus the electrical neutrality of each one is slightly altered, if this charged rod is suspended from a cord and a second charged rod is brought near, these are repelled between yes, however, if you rub a piece of skin against a plastic rod, it attracts the end of the suspended glass rod.
To explain this, it is then said that there are two kinds of charge, one of which (that of glass rubbed with silk) called positive and the other (that of plastic rubbed with skin) called negative. These simple experiments can be summarized as follows:
Charges of the same sign repel each other, and charges of the opposite sign attract each other.
The names of positive and negative referring to electric charge are due to Benjamin Franklin ( 1706 – 1790 ) who, in addition to outstanding activities, was an internationally renowned scientist.
Electrical forces between charged bodies have many industrial applications, including electrostatic paint spraying and powder coating, fly ash precipitation, non-impact ink jet printing, photocopying, among others.
Conductors and insulators
If you hold a copper rod, you can’t get it to be loaded, no matter how much you rub it with any material. However, if the rod is equipped with a plastic handle, it can still be loaded. The explanation is that the charge can easily flow through certain materials, called conductors, of which copper is an example.
In other materials called insulators, charges do not flow in most cases; If loads are placed on an insulator, like most plastics, the loads stay where they are placed. The copper rod cannot be charged because any charge you place will easily flow along the rod, through the human body (which is also a conductor), and to ground. However, the insulating handle blocks the passage and allows the copper to charge.
Glass, chemically pure water, and plastics are common examples of insulation. Although there are no perfect insulators, molten quartz is quite good, its insulating capacity is around 10 25 times that of copper (Cu).
Copper, metals in general, drinking water and the human body are common examples of conductors. In metals, an experiment called the Hall effect shows that negative charges (electrons) are those that can move freely.
When copper atoms unite to form solid copper, their outer electrons do not remain attached to each atom, but are free to move within the rigid lattice structure formed by the centers of the positively charged ions. These moving electrons are called conduction electrons.
The positive charges on a copper rod remain as motionless as they do on a glass rod.
Example 1.
A negatively charged plastic rod attracts either end of an uncharged, suspended copper rod. The conductive (moving) electrons on the copper rod are repelled by the negative charge on the plastic rod and move to the far end of the copper rod, leaving the near end of it with a net positive charge.
Example 2.
A positively charged glass rod also attracts an uncharged copper rod. In this case the conduction electrons in the copper are attracted by the positively charged glass rod towards the near end of the copper rod, the end furthest from it is then left with a net positive charge.
This distinction between conductors and insulators is more quantitative when considering the number of conduction electrons available in a given quantity of material. In a typical conductor, each atom can contribute one conduction electron and therefore there should be about 10 23 conduction electrons per cm 3 on average. In contrast, in an insulator at room temperature, it is generally unlikely to find even 1 conduction electron per cm 3 .
At an intermediate point between conductors and insulators are semiconductors such as silicon or germanium; a typical semiconductor can contain between 10 10 and 10 12 conduction electrons per cm 3 . One of the properties of semiconductors that makes them so useful is that the density of conduction electrons can be changed dramatically by small changes in material conditions, for example by introducing small quantities (less than 1 part in 10 9 ) of impurities or by varying the applied voltage, temperature or intensity of light that falls on the material.
