Static electricity

For science that studies static loads, see Electrostatic

The hairs of the girl are repeld with each other because of the positive electric charge acquired through contact with the slide.

The term static electricity refers to the accumulation of an excess of electric charge (positive or negative) in a conductive or insulating material. The effects of static electricity are familiar to most people because they can see, feel, and even feel the sparks of discharge that occur when an overcharged object is brought near a good electrical conductor (such as one connected to to ground) or another object with an excess charge but with the opposite polarity.

History

The phenomenon of static electricity has been known since antiquity, approximately since the 6th century BC. C. Scientific research on this phenomenon began when machines capable of generating static electricity could be built, such as the electrostatic generator built by William Thomson in the 19th century. The relationship between static electricity and storm clouds was not demonstrated until the 1850s by Michael Faraday.

Michael Faraday published in 1832 the results of his experiments on the nature of what until then were thought to be different types of electricity, showing that electricity induced by a magnet, photovoltaic electricity produced by a voltaic cell, and electricity static were of the same type. From this moment the study of static electricity was included in electricity in general.

Causes of static electricity

The materials we deal with in our daily lives are made up of atoms and molecules that are electrically neutral because they have the same number of positive charges (protons in the nucleus) as negative charges (electrons around the nucleus). The phenomenon of static electricity requires a sustained separation between positive and negative charges. Below are the main causes for this to be possible.

Induction of charge separation by contact

Electrons can be exchanged between two materials by contact and, furthermore, materials that have loosely bound electrons have a tendency to lose them while materials that do not have full outer shells of electrons have a tendency to gain them. This phenomenon is known as triboelectricity and results in one of the objects that have come into contact being positively charged while the other is negatively charged. The polarity and amount of net charge left to each material when separated will depend on their relative positions in the triboelectric series (a list that ranks materials based on their polarity and their ability to acquire charge). The triboelectric effect is the main cause of the static electricity that we observe in our daily lives and includes that which is produced by friction between different materials.

Separation of charges induced by pressure

Some types of crystals and ceramics have the property of generating a separation of charges in response to the application of a mechanical effort, it is what is called piezoelectricity, this is a phenomenon presented by certain crystals that when subjected to mechanical stress they acquire an electrical polarization in their mass.

Separation of charges induced by temperature

Some minerals, such as tourmaline, have the ability to be polarized by the effect of heat, which is known as pyroelectricity or the pyroelectric effect. All pyroelectric materials are also piezoelectric, the two properties being closely related to each other. Pyroelectricity is the ability to change the polarization of some materials subjected to temperature changes, generating an electrical potential, produced by the movement of positive and negative charges to opposite ends of the surface through migration.

Separation of charges induced by the presence of a charged object

A charged object, placed close to an electrically neutral one, will cause the other's charges to separate, since charges of the same polarity repel while those of different polarities attract. Since the force due to the interaction between electric charges decreases rapidly with increasing distance, the effect will be greater if they are very close. This effect is greater when the initially neutral object is an electrical conductor because charges have an easier time moving.

It is possible to induce a separation of charges and if the object is suitably grounded, leave it permanently charged. This is the system used by the Van de Graaff generator, a device commonly used to demonstrate the effects of static electricity.

Electrostatic discharge

The spark associated with static electricity is caused by the electrostatic discharge that occurs when the excess charge is neutralized by a flow of charges from the environment to the charged object or from it to its surroundings. In general, a significant accumulation of charges can only be persistent in areas of low electrical conductivity, in an environment where very few charges can move freely. The flow of neutralizing charges is often generated from neutral air atoms and molecules that are separated to form positive and negative charges, then move in opposite directions like an electric current, neutralizing the original buildup of charges. Air breaks in this way at about 30,000 volts per centimeter, this value depends on the humidity. The discharge heats the surrounding air and produces a bright spark, it also causes a shock wave that is the cause of the sound that can be heard.

The electric shock we feel when we receive an electrostatic discharge is due to the stimulation of the nerves when the neutralizing current flows through the human body. Thanks to the presence of water throughout the body and moving, charge accumulations do not become significant enough to cause dangerous currents.

A person walking on carpet can easily be charged up to 5,000 volts and produce a 30-amp pulsating discharge in a sensitive electronic circuit.

Lightning

Lightning is a natural electrostatic discharge.

Lightning is an example of an electrostatic discharge that can be observed in nature. Although the details are not entirely clear, the separation of charges is thought to be related to the contact that occurs between the ice particles that make up thunderclouds. But whatever the cause, the resulting lightning is nothing more than a large-scale version of the sparks we can see in household electrostatic discharges. The emission of light from the discharge heats the air around the channel that follows the electric current to a temperature that produces light by incandescence. The sound of thunder is the result of the shock wave that is created by the rapid expansion of superheated air.

Dangers

Effect of a discharge of static electricity on the surface of a radiographic film. The download has drawn a characteristic pattern in the form of "tree". This is a typical example of a radio device.

Despite its apparently innocuous nature, based on our experience in daily life, static electricity can have not insignificant dangerous effects in situations where the accumulation of charges occurs in the presence of sensitive materials or devices.

Electronic components

Many electronic components, especially semiconductor devices, are extremely sensitive to the presence of static electricity and can be damaged by electrostatic discharge.

Chemical industry

Electrostatic discharges can be very dangerous in places where you deal with flammable substances. A small spark is capable of igniting various explosive mixtures with devastating consequences. This is the case of factories that work with powdered substances in the presence of combustible or explosive materials.

Space exploration

Due to the extremely low humidity in the extraterrestrial environment, large buildups of static charges are possible and are a significant hazard to electronic devices used in spacecraft. It also represents a risk for astronauts, the fact of walking on such dry ground, such as that of the Moon or Mars, causes the accumulation of a significant amount of electrical charges that can cause electrostatic discharges capable of damaging the devices. electronics.

Refueling operations

If an electrostatic discharge occurs in the presence of fuel and its voltage is high enough, it can ignite the vapors given off from the fuel. This is a danger present at service stations and is one of the reasons why it is advisable to stop the engine while filling the vehicle with gasoline. This danger is also present at airports, during aircraft refueling operations.