Under normal conditions, most items are electrically neutral. But sometimes an electric charge – positive or negative – can accumulate on their surface or in the volume. This phenomenon is called electrification of bodies. It is studied in electrostatics – a branch of physics that considers stationary electric charges.
Electrification in physics
Electrification is a charge separation process in which electrically neutral bodies become charged. It can be described using such laws of physics as Coulomb’s law and the law of conservation of charge.
Coulomb’s laws and conservation of charge
Coulomb’s Law describes how charges act on each other. The force of their interaction (attraction or repulsion) is directly proportional to the product of their values and inversely proportional to the square of the distance between them. Opposite charges attract, identical charges repel.
The conservation law states that the algebraic sum of charges is conserved. If, as in the definition of a phenomenon, a positive charge has arisen on one object, a negative charge of the same magnitude must appear on the other.
An electric charge cannot exist without a carrier. This means that carriers – electrons – accumulate on bodies. The body with an excess of them is charged negatively, and with a deficiency – positively.
The names “negative” and “positive” for charges are arbitrary, the important thing is that they are of two different types.
Static electricity properties
Not only solids, but also liquids and gases can become electrified. Redistribution of ions occurs in them. Substances of different classes are electrified: dielectrics, semiconductors, insulated conductors.
When electrified objects are separated, the charge on them is preserved. The more bodies are removed from each other, the greater will be the potential difference across them.
When in contact with neutral or otherwise charged bodies, the charge can relax – spill over to another body, so a person in synthetic clothing can be “electrocuted” if he touches a metal battery or refrigerator. An electrical discharge can also occur through the air from a charged body to an uncharged one located at a certain distance.
How to electrify an object
You can create static electricity on a body surface in different ways:
- interaction with a charged object,
- with a sharp drop in temperature,
- exposure to ionizing radiation.
When an electrically uncharged body comes into contact with a charged object, it becomes electrified with the same sign.
When objects made of various types of materials are rubbed, opposite electric charges appear on their surfaces. The reason for the phenomenon is the difference in forces with which atoms or molecules interact. In short, we can say that a substance in which atoms or molecules are more strongly bound to each other attracts electrons to itself from another, where particles interact with less force.
Examples of the phenomenon
The very phenomenon of electrification was discovered back in Ancient Greece, when they noticed that when amber is rubbed with wool, it begins to attract dust, threads, and pile. This substance is called “electron” in Greek, hence the name of all phenomena associated with electricity.
Glass is positively electrified when rubbed against silk, negatively – ebonite when rubbed against wool. Everyone knows examples of electrification in everyday life, for example, hair is positively charged when combed with a plastic comb, and the comb itself is electrified negatively. Glass, paper, wool are charged positively, rubber, silicone, plastic are negatively charged.
Static electricity lasts the longest on objects if the air is dry. Humid air conducts electricity and objects quickly become electrified. In the presence of indoor plants, a boiling kettle, which increase humidity, static on clothes and hair appears less often.
A well-known example of electrolysis is lightning. This is an electrical discharge that slips between oppositely charged clouds or between a cloud and the ground. Charged thunderclouds can electrify various objects on the ground due to the redistribution of charges on them.
You can show the interaction of identically or oppositely charged bodies using ordinary tape. This requires two 12.5 cm strips of adhesive tape.
To demonstrate repulsion, the strips are glued to the table so that the 2.5 cm piece remains free. These hanging ends are attached to two pencils. If you suddenly tear off the tape from the table without touching it with your hands, the strips are electrified in the same way. Now they need to be separated at some distance and gradually brought closer together. At a certain distance, the repulsion of the stripes will be noticeable.
To demonstrate the attraction of oppositely charged bodies, one strip of adhesive tape is electrified, as in the previous experiment, and then placed on the table, sticky side up. Another strip, previously fixed on the pencil, is placed on the first one, and then torn off. Then the strips will be charged oppositely. As in the previous experiment, at a certain distance, one can notice the attraction of the stripes.
Danger of the electrification process
The charge on an electrified object can be quite large, and the voltage can reach tens of kilovolts, but because of the very small values of the current strength, it is not dangerous for humans.
However, such small discharges can have a negative effect on precision electronics, for example, microprocessors, therefore, when working with electronic components: during their manufacture, repair or use, special attention is paid to preventing electronisation.
Under some conditions, the relaxation of a large accumulated charge can lead to a fire. Airplanes become electrified in flight, so a discharge can occur when the ladder is brought in. To avoid this, static electricity is removed from the aircraft by dissipating it into the ground. For the same reason, a chain that is in contact with the ground is always attached to fuel trucks. This prevents the fuel from igniting.
Practical application of electrification
Static electricity build-up on objects can be dangerous, but there are positive aspects to this phenomenon as well. The electrification of bodies is used in practice in various fields:
- Electrostatic filters for air purification from pollution, mainly from dust, are used in everyday life and in industry.
- Electrostatic painting of surfaces such as cars. Electrified paint particles are attracted to the surface to be painted, resulting in less paint consumption.
- Artificial fur production. The finished pile is passed through the mesh, it acquires a charge and falls perpendicular to the base covered with glue.
- Smoking food using electrostatics.
Also, this phenomenon is used for sorting, filtering, purifying. Electrostatics are also used in medicine.
Electrification is associated with the appearance of an excess or lack of electrons on the surface or inside objects. You can create them in different ways, for example, by rubbing or touching a charged object. Electrification has practical uses, but in some cases it can be dangerous.