# Electromagnetism

Electrical and magnetic phenomena are an important and invisible part of our everyday lives. Every electronic device generates an electromagnetic field without us realizing  it .the light of the screen from which you are reading this page can be represented as electromagnetic waves that travel from the screen to your eyes. The study of these phenomena has led to the creation of a solid and complete theory that manages to explain a large number of the classical phenomena that have to do with charged particles or magnetic materials: electromagnetism.

## Electromagnetism definition

Electromagnetism is that part of physics that studies electrical and magnetic phenomena and how these are connected to each other. At this level, we will only deal with classical electromagnetism, but it is good to know that there is a branch of quantum physics called quantum electrodynamics that is dedicated to extending electromagnetism at the quantum level and not just classical.

Electromagnetism is that part of physics that studies electrical and magnetic phenomena and how these are connected to each other. Let’s briefly see what the study topics covered within electromagnetism are:

### Electrostatics and electrodynamics

Electrostatics and electrodynamics study electric fields and the charges that create them. These electric fields can be static (subject of study of electrostatics), generated by stationary charges or variable in time and space and linked to moving particles (in the case of electrodynamics).

These studies are particularly important because electric fields essentially constitute half of what the electromagnetic field is.

### Electric current

The study of electric current within electromagnetism has led to important developments regarding the union of studies on electric charges with those on magnetism. One of the most important discoveries is the fact that a circuit crossed by an electric current generates a magnetic field, and vice versa, the time-varying magnetic interaction is capable of generating an electric current!

This seemingly innocent discovery opened the door to the formalization of Maxwell’s equations and the unification of the two disciplines into what is electromagnetism.

### Magnetism

The last element of electromagnetism to be defined is magnetism. Let’s see a very simple definition: Magnetism is that phenomenon that is observed in everyday life when we observe a magnet or a compass. In fact, it is the branch that studies the properties of materials to attract ferrous objects.

Like electrostatics, which is based on the existence of opposite charges that exert forces of attraction towards each other, magnetism is based on the existence of elements of an opposite nature: the magnetic poles. The substantial difference between the two systems is that there are no magnetic monopoles, i.e. elements that present only one of the two polarities.

### Maxwell’s equations and unification of electromagnetism

Maxwell’s equations are the fundamental pillar of electromagnetism. They express how the Electric field and magnetic are linked, what are the constraints of this interaction and their temporal evolution. These four equations group together equally important laws of electrodynamics and magnetism, extending them and showing the symmetry that binds electricity and magnetism. Let’s look briefly at what these laws are and how they can be described locally in a vacuum.

#### Gauss’s law for the electric field

This law, also called the “law of electric flow”, describes the relationship between the electrostatic field and the electric charges that generate it by putting Lightthat the flow of the electric field through a closed surface depends on the charge contained within it.

#### Gauss’s law for the magnetic field

Gauss’ law for the magnetic field says that there is no equivalent of electric charges with regards to magnetism (the so-called monopoles), but that only magnetic dipoles exist. Not only that, this law also talks about the flow (of the magnetic field this time) and states that the flow of a magnetic field through a closed surface will always be zero.

This law describes the induction of an electric field by a time-varying magnetic field, a fundamental principle for some types of generator.

#### Ampère-Maxwell’s law

This law describes how magnetic fields can be generated, and in particular it states that a magnetic field can be created through simple electric currents, or by variable electric fields (the so-called displacement current).

## Electromagnetic field

The electromagnetic field is the direct and logical consequence of the equations of Maxwell’s equations; these equations, together with theForceof Lorentz, can describe the properties and characteristics of the electromagnetic field. This field is present locally wherever there is a distribution of electric charge orElectric currentvariable over time and propagates asElectromagnetic waves.

As we said, it is formed by the union of the electric and magnetic fields, perpendicular to each other and which propagate with speed (in vacuum)�=⋅�≊3108�/�in the direction defined by the vector product between the vectors of the two fields. In this questionrepresents the wavelength ethe frequency of electromagnetic radiation associated with the field. Furthermore, the two fields always oscillate in phase, and their intensities are linked by the relationshipAND=, which shows us that when one of the two is null, so is the other.

The propagation of the electromagnetic field gives rise toWhere electromagnetic which propagate in vacuum at speed , while in media they propagate with a velocityin=/Whererepresents the refractive index of the medium in which it propagates.

## Electromagnetic spectrum

The electromagnetic spectrum is the set of wavelength (or frequency) values ​​of electromagnetic waves. Our eye is able to see only a part of these frequencies (what we call visible light) and that is in the range between≈390It is760which correspond to violet and red.

However it Electromagnetic spectrumit goes far beyond what we can see. Below we see a table with the main classifications of Whereel ectromagnetic waves based on their wavelengths:

 Name ���� ���� Gamma rays – 10−11� X-ray 10−11� 10−8� Ultraviolet rays 10−8� 4⋅10−7� Visible 4⋅10−7� 8⋅10−7� Infrared 8⋅10−7� 10−3� Microwave 10−3� 10−1� Where Radio 10−1� –