The electromagnetic spectrum comprises several subranges, hereby popularly known as portions. The various parts in the electromagnetic spectrum come about based on behavior in emitting, transmitting, and absorbing the corresponding waves.

What is the electromagnetic spectrum simple definition?

The electromagnetic spectrum is defined as the whole distribution of electromagnetic radiation based on wavelength and frequency.
From the shortest wavelength to the longest (highest to lowest frequency), the entire electromagnetic spectrum comprises gamma rays, X-rays, Ultraviolet radiation, visible light, infrared radiation, and radio waves.

What are the seven types of the electromagnetic spectrum?

The electromagnetic spectrum is a very broad term and contains seven different types of waves.

The Electromagnetic Spectrum. Source: Britannica

Radio waves

The emission and reception of radio waves are made possible through antennas and range between 300 gigahertz (300GHz) and 30 hertz (Hz). These are made from conductors like metal rod resonators and are used by all radio devices, starting from small pocket radios to radio stations.

Artificial generation of radio waves happens when a transmitter generates the alternating current (AC) that is then applied to the antenna. The antenna’s oscillating electrons would then create oscillating magnetic and electric fields. These fields then radiate out energy from the antenna in the form of radio waves.

Radio waves help transmit data across great distances, which happens in radio broadcasting, two-way radios, television wireless networking, communication satellites, and mobile phones.

Microwaves

When radio waves are of short wavelength, they are termed microwaves. This length ranges from one millimeter to ten centimeters (300 MHz – 300GHz). Apart from Magnetron and klystron tubes, microwave energy is also produced by solid-state devices such as IMPATT and Gunn diodes.

Microwave penetrates materials to deposit their energy under the surface. This is unlike the higher energy and frequency waves like visible light and infrared, which are usually absorbed at the surface level. The effect is used in microwave ovens to heat food. The same also applies to medical diathermy and industrial heating.

Infrared radiation

This small portion of the electromagnetic spectrum extends the long wavelength to the microwave range. Unlike light, it is usually invisible to human eyes but can be felt in the form of a warm sensation on the skin. All objects found in the universe emit infrared, but the most obvious sources are fire and the sun. Infrared covers the range of 300 GHz to 400 THz and is divided into three main parts:

  • Far-Infrared – From 300GHz to 30 THz
  • Mid-Infrared – From 30 THz to 120 THz
  • Near-Infrared – From 120 THz to 400 THz

Visible Light

Visible light is the portion of the EM spectrum most sensitive to human eyes. Sometimes referred to as near-infrared light, the absorption and emission of visible light are made possible by electrons in atoms and molecules that hop from one higher energy level to another.

Notably, the human visual system is triggered by a minute portion of the EM spectrum in the form of light. The human eyes can detect any radiation with a wavelength of between 400 and 790 THz (380-760 nm), which is ultimately light energy the human eyes can perceive.

Ultraviolet Radiation

Ultraviolet (UV) rays’ wavelength is longer than the X-ray but shorter than the violet end of visible light. UV light stands out as the longest wavelength radiation that can ionize atoms through its energetic photons, unlike visible light. This separates electrons from atoms, thus leading to chemical reactions.

Apart from light, the sun is known to emit significant portions of UV radiation. This includes a very short wavelength that can potentially destroy life forms on land. However, the damaging UV wavelengths of the Sun’s rays get absorbed in the earth’s atmosphere, making them safe before reaching the surface.

X-rays

Unlike visible light, X-rays have higher electromagnetic energy that can penetrate most objects, including flesh. Like UV’s upper ranges, X-rays are also ionizing. X-ray interacts with matter through the Compton effect, and its frequencies range from 30 petahertz to 30 exahertz. They then fall into two primary forms: hard and soft X-rays. Soft X-rays have longer wavelengths compared to hard X-rays.

X-rays are applicable as probes in high-energy physics and play a vital role in medical X-ray imaging.

Gamma Rays

Gamma rays come in just after X-rays but with wavelengths less than 10 picometers (PM) and frequencies greater than 1019 Hz. Discovered in 1990 by Paul Villard, Gamma rays impart the highest photon energy. This is especially so considering their wavelength does not have a defined lower limit. They are applicable in astronomy when studying high electromagnetic energy regions or objects.

Gamma rays are commonly used to irradiate seeds and foods for sterilization. In the medical fraternity, gamma rays are used in radiation gamma therapy. Gamma’s wavelengths can be measured accurately through the Compton Scattering Effect.

Why is it called the Electromagnetic Spectrum?

It takes this name because of the interrelation of electric fields or currents and magnetic fields. Since the classification of these portions is based on their positioning and electromagnetic radiation, it then becomes an electronic spectrum.

Measurement of EM radiation can be done in terms of wavelength, energy, or frequency. Wavelength is measured in terms of meters, while frequency uses Hertz or cycles per second. Energy, on the other hand, uses electron volts as its unit of measurement. The relationship between these three units of measurement is mathematical in nature.

While astronomers studying radio waves use frequencies or wavelengths, a bigger portion of the radio part in the electromagnetic waves spectrum is the 1 cm to 1 km range. This means radio takes a bigger junk of the EM spectrum.

The wavelengths of Ultraviolet, X rays, and gamma rays portions of the EM spectrum are extremely small. As such, astronomers would rather refer to these photons by their energies instead of using wavelengths. These energies are measured in electron volts (eV).

Why do astronomers put telescopes in orbit?

Most electromagnetic radiation emitted from space cannot get to the earth’s surface because it is absorbed in the atmosphere. Some ultraviolet light, visible spectrum light, and radio frequencies can, however, reach sea level. As such, astronomers put telescopes on mountaintops to help them observe infrared wavelengths. Balloon experiments can continue for months and may reach 35 km above the earth’s surface. On the other hand, rocket flights can swiftly take instruments above the earth’s atmosphere but require bigger funding.

The electromagnetic spectrum touches our everyday lives much more than we could think. For example, as a generic term that covers anything related to electromagnetic radiation, scientists have used the electromagnetic spectrum to make discoveries and uncover things that had hitherto been deemed impossible.