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Magnetic effect of electric current - Electrical energy .. Physics

Magnetic effect of electric current

Magnetic fields are closely related to electric fields. Hans Oersted discovered in 1819 that the passage of electric current in a straight wire leads to the creation of a magnetic field whose axis is the wire and its direction varies depending on the direction of the current itself. It is worth noting that the passage of electric current in two parallel wires leads to the creation of an attractive force between them if the direction of the current in each of them is different from the other, and to a repulsive force if the currents in them are in the same direction. Here we can redefine the ampere as the value of a current passing through two parallel wires, of infinite length, separated by a distance of one meter and subject to a force of 2 × 10 - 7 Newtons for every meter of their length.

The circular coil is characterized by dense lines of force inside it, and its field is similar to the field of a permanent magnet rod, and the electromagnet is a wire wrapped around an iron magnetic core with a weak magnetic property, and the intensity of its field is directly proportional to the intensity of the current and the number of turns in it, and inversely proportional to its length. During the passage of current in it, its core becomes magnetized, so the intensity of the field increases in it when the current is cut off, it loses all magnetism. As for its magnetic properties. When the lines of force change around a coil in which an electric current is passing, induced electromotive forces are generated in it, the value of which is proportional to the rate of change of the magnetic field per unit area (magnetic flux). This law is known as Faraday's law of electromotive induction. The direction of the electromotive force is such that it is always facing the change that generated it - Lanz's law. This effect is of great importance in alternating current (i.e. in which the direction of electron flow is periodically reversed - see p. 48). Therefore, when an alternating current passes through a coil, a changing magnetic field is generated in it, which induces an electromotive force in the coil with a direction opposite to the passage of the current itself. The induced voltage is proportional to the rate of change of the current itself. The proportionality constant is called the self-inductance coefficient and is measured by a unit called Henry. It represents the self-inductance resulting from a rate of change of the current with a value of one ampere, which results in an induced voltage with a value of one volt. Inductive coils are elements of great importance in electrical circuits.

When an alternating current passes through a coil (primary) surrounding an iron core, it produces an induced voltage in another coil separate from it (secondary), but magnetically coupled to it. This voltage generates a secondary current opposite to the first, and with the same frequency. As for the value of the induced voltage in the secondary coil, it is proportional to the rate of change of current in the primary coil. (The magnetic effect of electric current. Parallel wires repel each other if two opposing currents pass through them (A), and are attracted to each other. If the currents are in the same direction (B). A field similar to the field given by the magnetic rod is generated from a current in a coil (C), and this phenomenon can be magnified by increasing the number of turns (D).

This constant of proportionality is called the mutual inductance coefficient M. It is measured in the same unit as the self-inductance - the Henry. This device is known as a transformer, and is used to raise or lower the voltage. There are equations that link the number of turns in the primary, N, and the induced current in it, Y, and the induced voltage, C, on the one hand, and the number of turns in the secondary, N, and the induced current in it, Y, and the induced voltage, on the other hand, and these equations are: N1 / N2 = Y2 / Y1 = C1 / C2.

(The electromagnetic wave consists of Two fields, one electric and the other magnetic, are variable and perpendicular to each other)

There are two types of transformers: the step-up transformer that increases the value of G2/G1 and the step-down transformer that reduces it. Both types have great value in electricity transmission (see p. 50).

It is worth noting that the movement of any charged particle, including electrons, leads to the creation of a specific magnetic field. When a charged particle enters a magnetic field perpendicular to its line of motion, it becomes subject to a force that is perpendicular to the directions of the field and the particle's motion at the same time, and leads the particle to move in a circular line that varies in length with the particle's speed and the intensity of the magnetic field. However, if the particle enters the magnetic field parallel to it, in this case it moves in a spiral line around one of the existing lines of force.

In 1864, James Clerk Maxwell derived four equations known as Maxwell's equations, which later made it possible to understand all the relationships between electricity and magnetism, regardless of the conditions applied. These equations showed that the electric field is always accompanied by a magnetic field, and that the field resulting from the acceleration of a charged particle goes in all directions and consists of a changing magnetic field and an electric field perpendicular to it, both of which are perpendicular to the velocity of the particle. This type of field was known as electromagnetic radiation, and the most prominent examples of it are light and radio waves.