Actually, we are all surrounded by electromagnetic radiation. The light we see around us is a type of electromagnetic radiation. However, it is a small part of the electromagnetic spectrum. In addition to this visible light, many other rays surround us that are not visible to our naked eyes such as radio waves, microwaves, infrared rays, ultraviolet rays, x-rays, and gamma rays. These are all electromagnetic radiation.

If you do not know much about it, this article is for you. Today, I am going to unlock the details of electromagnetic radiation. In this article, you will know -

1. What is Electromagnetic Radiation?
2. What is Electromagnetic Theory?
3. What is Electromagnetic Spectrum?
4. Measuring Electromagnetic Radiation

# What is Electromagnetic Radiation?

Electromagnetic (EM) radiation is a type of energy that is always present around us and takes many forms, such as radio waves, microwaves, infrared rays, ultraviolet rays, x-rays, and gamma rays. The sunlight ( visible light ) we see is also a type of electromagnetic radiation which is a small part of the electromagnetic spectrum. But the different colors of visible light contain a broad range of electromagnetic wavelengths.

This electromagnetic radiation refers to the waves of the electromagnetic field, which propagate through space and carry electromagnetic radiant energy. In a vacuum, the speed of electromagnetic radiation is the same as the speed of light.

## What is Electromagnetic Theory

At one time the electric force and the magnetic force were thought to be two different forces. But in 1873, Scottish physicist James Clerk Maxwell, brought the correlation between electricity and magnetism for the first time using Maxwell’s equations and developed a unified theory known as electromagnetic theory (electromagnetism).

This electromagnetic theory deals with the interaction between an electric field and a magnetic field. The stationary charge creates an electric field around it and the moving charge creates a magnetic field around it.

The direction of the oscillation of the electric field and the magnetic field is always perpendicular to each other, and the transverse electromagnetic wave which generates from it propagates at the speed of light. The propagation of this wave is always normal to these oscillating electric and magnetic fields.

This theory discusses how electrically charged particles interact with each other and with magnetic fields. If we talk about the interactions between them then there are four main electromagnetic interactions and these interactions are as follows :

1. The force of attraction or repulsion that acts between electric charges is inversely proportional to the square of the distance between them.

2. Two different magnetic poles ( North pole and South pole ) always attract each other and two similar magnetic poles ( North pole and North pole or South pole and South pole ) always repel each other, much as electric charges do.

3. The current flowing in a wire produces a magnetic field whose direction depends on the direction of the current flowing.

4. Just as a moving electric field produces a magnetic field, so a moving magnetic field also produces an electric field.

This electromagnetic theory can be better understood by Maxwell's equations. If we talk about Maxwell's four important equations, they are as follows :

Where, ρ = net charge inside the surface, ε0 = represents permittivity of vacuum, B = the magnetic field, E = electric field, and J = the current density

## What is Electromagnetic Spectrum?

All these electromagnetic radiations (from radio waves to gamma rays) are plotted according to the intensity of light at different frequency range or distribution of wavelength and frequency. This range in the distribution of wavelength and frequency of all types of electromagnetic radiation is called the electromagnetic spectrum.

## Measuring Electromagnetic Radiation

Electromagnetic radiation can be measured in terms of energy, wavelength, and frequency. Energy is measured in the unit of electron volts (eV). Wavelength is measured in the unit of meters (m). Frequency is measured in the unit of Hertz (Hz) or cycles per second.

here are the wavelength and corresponding frequency ranges of some electromagnetic radiations -

Wavelength range - 1 millimeter (mm) to 10,000 kilometers (km)s
Corresponding frequency range - 300 gigahertz (GHz) to 30 hertz (Hz)

Microwaves:

Wavelength range - 1 millimeter (mm) to 1 meter (m)
Corresponding frequency range - 300 gigahertz to 300 megahertz (MHz)

Infrared rays:

Wavelength range -  700 nanometers (nm)s to 1 millimeter (mm)
Corresponding frequency range - 430 terahertz (THz) to 300 gigahertz (GHz)

Visible rays:

Wavelength range - 380 nanometers (nm)s to 740 nanometers (nm)s
Corresponding frequency range - 405 terahertz (THz) to 790 terahertz (THz)

Ultraviolet rays:

Wavelength range - 10 nanometers (nm)s to 400 nanometers (nm)s
Corresponding frequency range - 30 petahertz (PHz) to 750 terahertz (THz)
Energy range - 1 eV to 100 eV

X-rays:

Wavelength range - 10 picometres (pm) to 10 nanometres (nm)s
Corresponding frequency range - 30 petahertz (PHz) to 30 exahertz (EHz)
Energy range - 100 eV to 100,000 eV (or 100 keV)

Gamma rays:

Wavelength range - less than 100 picometers (pm)s
Corresponding frequency range - greater than about 10^19 cycles per second, or hertz (Hz)
Energy range - greater than 100 keV

The longer the wavelength of the wave, the lower its frequency. Similarly, the higher the frequency of a wave, the shorter its wavelength. This can be measured by using this simple formula

𝜈 = c/λ

Where 𝜈 is referred to as frequency, c is the speed of light and λ is the wavelength of electromagnetic radiation.

The wavelengths of ultraviolet rays, x-ray, and gamma-ray regions of the EM spectrum are very small. That's why scientists prefer to interpret these rays of the electromagnetic spectrum with their energy. This can be measured by using this simple formula

E = h𝜈   ( h = plank's constant)