Common electrical concepts

Electric charge

Electric charge is a property of a certain group of subatomic particles, and it is the reason for generating as well as interacting with the electromagnetic force. The electromagnetic force is one of the four fundamental forces of nature. The charge originates in the atom, the most famous carriers of which are the electron and proton. It is also a stored quantity, or in other words, the charge inside an isolated system will remain constant regardless of any changes that occur within this system. It is possible for the charge to be transferred between objects within the system, either through direct contact or passing through a conductive material, such as a wire. . The term “static electricity” refers to the presence (or imbalance between) charges on an object. This usually happens when different materials are rubbed together and charge is transferred from one material to another.

The presence of an electric charge is what generates the electromagnetic force: charges push each other with force, and this effect has been known since ancient times although it is not understood. It is possible to charge a lightweight ball suspended from a wire by touching it to a charged glass rod by rubbing it against a piece of cloth. If another similar ball is charged with the same glass rod, it is observed that it repels the first ball; The electric charge will push the two balls away from each other. The two charged balls also repel each other by coming into contact with an amber rod that has been rubbed against a piece of cloth. However, if the first ball is charged with the glass rod and the second with the amber rod, they will be attracted to each other. Charlie Augustin de Coulomb investigated these phenomena in the eighteenth century and concluded that electric charge appears in two opposite forms. This discovery led to the well-known axiom that:Similar electric charges repel each other, while different charges attract .

The force acts on the charged particles themselves, so the charge tends to spread as evenly as possible over a conductive surface. Whether it is attraction or repulsion through Coulomb’s law, which forms a relationship between force and the product of charges, and between force and the inverse square of the distance between them. This discovery led to the famous axiom: “ The force of repulsion between two small spherical bodies charged with the same type of electricity is inversely proportional to the square of the distance between their centers .” The electromagnetic force is very strong, second only to strong interactions. But unlike that force, the influence of electromagnetism extends across all distances. Compared to the weaker force of gravity, the electromagnetic force pushing two electrons apart is about 10 ⁴² times greater than the gravitational force pulling them together.

The electric charge on the electrons and protons is opposite, so the amount of charge is described as negative or positive. It is customary to consider the charge carried by electrons as negative and that carried by protons as positive. This custom began with the works of Benjamin Franklin. The amount of charge is usually denoted by the symbol “Q” and expressed in coulombs. Each electron carries the same charge, which is approximately -1.6022×10 ⁻¹⁹  coulombs. The proton carries a neutral and opposite charge, equal to +1.6022 x 10 ⁻¹⁹  coulombs. Electric charge is not limited to matter only, but also exists in antimatter. Every antiparticle carries a charge equal to and opposite to its counterpart.

In addition, it is possible to measure electric charge by several means, such as the gold-leaf electroscope, which contains two thin strips of gold leaf hanging in a glass container, moving away from each other when they charge, and the angle of their movement depends on the amount of charge. Although this detector is still used in classroom demonstration experiments, it has been replaced by the electron electrometer.

electric current

The movement of electric charge is known as electric current, the intensity of which is usually measured in amperes. An electric current consists of any charged and moving particles. Electrons are the most common of these particles, but any moving charge can be a current. By convention, positive current is defined as current flowing in the same direction as any positive charge it carries; Or it is the current flowing from the maximum positive terminal in the electrical circuit to the maximum negative terminal. This type of current is called conventional current. Therefore, the movement of negative electrons around an electrical circuit – one of the most common forms of electric current – is positive in  the direction opposite the direction of the electronsHowever, depending on the surrounding conditions, an electric current can consist of the flow of charged particles (charged particle) in either direction or even in both directions simultaneously. The terms negative and positive are commonly used to simplify this situation.

Furthermore, the process by which an electric current passes through a material is called “electrical conduction.” The nature of electrical conduction differs from the nature of the charged particles and the matter through which it passes. Examples of electric currents include metallic conduction, in which electrons flow through a conductor such as a metal. In addition, there is electrolysis in which ions (which are charged atoms) flow through liquids. While the particles themselves move quite slowly, sometimes on the order of fractions of a millimeter per second, the electric field through which these particles flow is itself propagating at close to the speed of light, allowing electrical signals to pass quickly through the wires. Electric current produces several noticeable effects that were once considered the way people perceived the presence of an electric current. In 1800, William Nicholson and Anthony Carlyle discovered that an electric current could break down water from a voltaic battery, a process now known as electrolysis. Michael Faraday extensively studied Nicholson and Carlyle’s discovery in 1833.

The current passing through resistance causes a kind of heating in the surrounding space, an effect that James Prescott had investigated mathematically in 1840. One of the most important discoveries regarding electric current was what Hans Christian Oersted reached by chance in 1820 when he was attending one of his lectures. He found that an electric current in a wire disturbs the movement of a magnetic compass needle. He also discovered electromagnetism, which is a basic interaction that occurs between electricity and magnets.

In engineering applications and in homes, electrical current is usually described as either direct current or alternating current. These two terms refer to how electric current changes in terms of time. The direct current, which is produced from a battery, for example, and which is necessary to operate most electronic devices, flows in one direction from the positive end of the electrical circuit to the negative end of it. If the electrons move or carry this flow, which is more common, they will pass in the opposite direction. Alternating current is any current whose direction is repeatedly reversed.

This current often takes the form of a sine wave. Thus, the alternating current oscillates back and forth within the conductor without the electric charge moving any distance over time. The average period of time for the alternating current is zero. However, it conducts energy in one direction, which is first and then reflects. Alternating current is affected by electrical properties that are difficult to observe in the steady state of direct current. Examples of these properties are: inductance and capacitance. However, these properties become more important when a set of electrical circuits experiences a temporary fluctuation in current, such as when power is first supplied to it.

Electric field

Main articles: Electric field, electrostatics, and static electricity

Michael Faraday talked about the concept of an electric field. He said that it arises through a charged body in the space surrounding it, and exerts a force on any of the other charges within the field. The electric field between two charges works in the same way as the gravitational field works between two masses (mass). The electric field, like the gravitational field, expands to infinity and shows an inverse square relationship with distance. However, there is an important difference between them:

Gravity always acts on an element of attraction, attracting two masses towards each other. While an electric field may cause particles to attract or repel. Since large objects, such as planets, typically carry no net charge, the electric field at a distance is zero. Thus, gravity is the dominant force in the universe, although it is weak compared to other forces.

In general, the space occupied by an electric field varies, and its intensity at any point is defined as the force (per unit charge) that a fixed, negligible charge would feel if placed at that point.

The imaginary charge, called a “test charge,” must be very small to prevent its electric field from disturbing the main field. It should also be fixed to prevent the influence of magnetic fields (magnetic field). Since the electric field is defined in terms of force, and since force is considered a vector, it follows that the electric field is also a vector and has both magnitude and direction. More precisely, the electric field is a vector field.

In addition, the study of electric fields created by fixed charges is called static electricity. The electric field can be depicted through a set of imaginary lines whose direction at any point is the same as the direction of the field. Faraday is considered the first to introduce this concept. Faraday’s term “lines of force” is still sometimes used. Field lines are paths created by a positive charge. Because she had to move within this field. However, these lines are an imaginary concept that has no physical existence. The field permeates the space between the lines.

The field lines emitted by fixed charges have several main properties. The first property is that it originates with positive charges and ends with negative charges, and the second property is that it must enter any good conductor at right angles. The third characteristic is that they do not intersect or encircle themselves.

Any hollow conductive body carries all of its electrical charges on its outer surface. Accordingly, the electric field is zero in all places inside the body.

This is the main operating principle on which the Faraday cage depends, which is a conductive metal structure that isolates what is inside it from external electrical influences. Static electricity is particularly important when designing high-voltage equipment elements. There is a certain limit at which the intensity of the electric field that can be resisted by any medium ends. Otherwise, electrical breakdown occurs and the arc causes a transient flashover between the charged parts. For example, air travels in a curved path through small gaps where the electric field strength exceeds 30 kilovolts per centimeter. In larger gaps, the intensity of the electrical breakdown is weaker, probably reaching kilovolts per centimeter.

The clearest natural phenomenon that indicates this is lightning. It occurs when electrical charges in the clouds are separated by rising air columns and when the charges raise the electric field in the air more than they can bear. It is possible for the electrical voltage in one of the large lightning clouds to increase until it reaches 100 megavolts and may discharge a huge amount of energy that may reach 250 kilowatts per hour.

The field strength is greatly affected by nearby conducting objects, and is especially strong when it is forced to bend around pointed objects. This principle is used in lightning rods. It is a metal pole with a pointed tip that absorbs the electrical current resulting from lightning strikes, instead of it falling on the building it protects.

Electric potential difference

The concept of electric potential is closely related to the electric field. A small charge inside the electric field experiences a force, and it takes some work to move that charge to that point that opposes the force.

The voltage at any point is defined as the energy required to slowly bring a unit of test charge from an infinite distance to that point. Electrical voltage is usually measured in volts. One volt is the voltage that a joule of work must consume to produce a coulomb of infinite electrical charge.

 Although the definition of voltage is conceptual, it has a simple practical aspect. The most important concept is the electric potential difference, which is defined as the energy needed to move a unit of charge between two specific points.

The electric field has a special property: it is “conservative” – which means that the path the test charge takes does not matter: all paths between two specific points consume the same amount of energy. Thus, a characteristic value of the potential difference can be determined.

 Voltage is known as a unit for measuring and describing the difference in electrical potential, so that the term electric voltage has greatly increased its daily use.

For practical purposes, it is useful to identify a common reference point through which efforts can be expressed and compared. While this may be infinite, the most useful reference is the Earth itself, whose voltage some assume does not change anywhere. This reference point is usually called the ground (in British dialect “Earth” and in American “Ground”). It is assumed that the Earth is an infinite source of equal amounts of positive and negative charges.

Therefore, they are not electrically charged and are not rechargeable. Electric potential is a scalar or scalar quantity, meaning it has only magnitude and no direction. It can be considered analogous to height: just as a free body falls at different heights due to gravity, so an electric charge falls at different potentials due to the electric field.

Just as stereo maps show contour lines showing points of equal height, it is possible to draw a set of lines showing points of equal electrical potentials (known as isopotentials) around a statically charged object. These lines pass through all the lines of force at right angles.

It must also extend parallel to the surface of the conductor, otherwise it would produce a force on the charge carriers and the field would not become static. An electric field was previously defined as the force exerted per unit charge, but the concept of electric potential allowed for a more useful synonymous definition: an electric field is a local gradient of electric potential. Usually expressed in volts per meter, the direction of the electric field vector is the line of greatest potential gradient and is the line where the equipotential lines are close to each other.

Electromagnetism

Oersted’s discovery in 1821 of the existence of a magnetic field around all sides of a current-carrying wire demonstrated a direct relationship between electricity and magnetism. Moreover, the interaction seemed different from gravitational force and electrostatic force, two forces of nature that were discovered later.

 The force on the compass needle did not direct it toward or away from the current-carrying wire, but it acted at right angles to it. Here are Oersted’s slightly ambiguous words: “ The electrical opposition works in a rotating way». The force also depended on the direction of the current, so if the flow reversed, so did the force. In fact, Oersted did not fully comprehend his discovery, but he noted that the effect was reciprocal or inverse, meaning that the current exerted a force on the magnet and the magnetic field exerted a force on the current. André-Marie Ampere investigated this phenomenon further and discovered that two parallel wires carrying electric current exert a force on each other: that is, two wires conducting electric current in the same direction are attracted to each other, while two wires carrying current in opposite directions repel each other. The magnetic field produced by each current mediates this interaction, which is the basis of the international definition of the ampere.

An electric motor uses an important effect related to electromagnetism: an electric current passing through a magnetic field experiences a force at right angles to both the field and the current.

The relationship between magnetic fields and electric currents is very important. It led to Michael Faraday’s invention of the electric motor in 1821. The Faraday motor, a unipolar motor, consists of a permanent magnet placed inside a tub of mercury. An electric current was conducted in a wire suspended from a magnet and dipped in mercury. The magnet exerts a tangential force on the wire, causing it to rotate around the magnet throughout the period of electric current flow.

An experiment conducted by Faraday in 1831 revealed that a wire moving perpendicularly toward a magnetic field creates a potential difference between its ends. Further analysis of this process, known as electromagnetic induction, also allowed him to establish the principle now known as Faraday’s law of magnetic induction. This law states that the potential difference induced within a closed circuit is proportional to the rate of change of magnetic flux through the circuit. Using this discovery, Faraday was able to invent the first electric generator in 1831.

In this generator, Faraday converted the kinetic energy of a rotating copper disk into electrical energy. Although the Faraday disk was inefficient and limited as a practical generator, it demonstrated the possibility of generating electrical power using magnetism. Those who followed him benefited greatly from his work. The work of Faraday and Ampere revealed that a time-varying magnetic field acts as a source of an electric field, and that a time-varying electric field acts as a source of a magnetic field. Therefore, when the time of either field changes, the field of the other is necessarily induced.

 This phenomenon has the characteristics of a wave and is commonly referred to as an electromagnetic wave. James Clerk Maxwell analyzed electromagnetic waves theoretically in 1864. Maxwell also developed a set of equations that clearly describe the interrelationship between electric field, magnetic field, electric charge, and electric current.

In addition, he was able to prove that this wave would necessarily travel at the speed of light, and therefore light itself is a form of electromagnetic radiation. Maxwell’s laws, which link light, fields, and electric charge, are considered one of the greatest achievements of theoretical physics.