According to classical physics, electromagnetic radiation is a wave of electrical and magnetic energy that propagates through space (vacuum) at the universal speed of light (2.998 x 108 m/s). The electrical and magnetic fields are synchronized in time but oscillate perpendicular to each other (i.e., at 90 degrees). Electromagnetic radiation or waves are transverse waves which means that the direction of oscillations is perpendicular to propagation. If you plot the directions of oscillations of the electric field and the magnetic field and the direction of propagation of the wave, they will be at 90 degrees to each other, forming a three-dimensional coordinate system.

In quantum mechanics, electromagnetic radiation is viewed as consisting of photons that are elementary particles with zero rest mass and responsible for all the properties of electromagnetic radiation. The photons are packets of radiant energy which travel through space. The photon's energy is quantized and is related to the frequency of the radiation by the Planck equation, E = hf where E is the energy of the photon, h is Planck’s constant, and f is the frequency of the electromagnetic radiation. Since h is fixed, the energy of an EMR is directly proportional to its frequency. That is why high-frequency gamma rays carry energy that is 5 orders of magnitude greater than radio waves.

Electromagnetic radiation is produced when a charged particle is accelerated or decelerated. The change in velocity causes the charged particle to emit quantized packets of energy in the form of electric and magnetic fields. For example, in a radio antenna, a charged particle emits electromagnetic radiation when it oscillates at the desired frequency. The emitted radiation travels through space and will affect any substance it comes in contact with by transferring energy to the substance's atoms. Hence you can make another radio receiver to receive signals from an antenna by having an oscillating circuit with the same frequency as the antenna.

All electromagnetic radiation is characterized by wavelength, velocity, and frequency. The relationship between the three is given by the equation:

c = wf

Where c is the velocity of the electromagnetic radiation and is constant at 2.998 x 108 m/s

w is the wavelength of the electromagnetic radiation

f is the frequency of the radiation

Since all electromagnetic radiation propagates through space at the same speed limit, the only variables that differentiate electromagnetic radiations are frequency and wavelength. The relationship between wavelength and frequency is indirect, which means that higher frequencies have shorter wavelengths.

Electromagnetic radiations are grouped based on their frequencies, and that grouping forms what is called the electromagnetic spectrum. The grouping includes:

• Long Radio Waves: these form the lowest range of the electromagnetic spectrum. Frequencies of long radio waves range from 3Hz to 106 Hz. The corresponding range of wavelengths for long-range radio waves is 0.5m to 100km. The long-range radio waves' energy levels are very low and therefore are unable to affect biological materials.
• Radio Waves: these are the second-lowest radiations on the spectrum. Their frequencies range from 106 Hz to 109 Hz. The corresponding wavelength of radio waves is in the range of 100 m to 103 m. Radio waves are used in radio stations, TV broadcasting stations, and satellite communications. Radio waves are also used in navigation and air traffic control. Although radio waves' energy levels are higher than the long-range radio waves, they are still low and therefore not harmful to biological materials.
• Microwave: these are found in the EMR spectrum after radio waves. They have frequencies ranging from 3 x 109 Hz to 30 x 1012 Hz. The corresponding wavelength range for microwave is 10-4 m to 10-2 m. Microwave is used in home microwaves for heating and warming of food items. Microwaves are also employed in high-speed data transfer between stations on Earth. Modern space probes also use microwaves for communication. The Global Positioning System (GPS) uses microwaves as well.
• Infrared Rays: these are found in the electromagnetic spectrum after microwaves. They are in the frequency range of 300 x 1012 Hz to 400 x 1012 Hz with wavelengths ranging from 10-9 m to 10-6 m. Hot objects emit infrared. It is used in electric cookers, heaters, and night vision goggles that can detect the infrared emitted by people in the dark. Infrared is also used in short-range communications such as in TV remote controls and IR access control cards. Although we can’t see infrared, we can feel it with our skin if the intensity is high.
• Visible Light: this is the range of the EMR spectrum which is visible to the human eye. Its frequencies range from 400 x 1012 to 800 x 1012. Its wavelengths range from 740 x 10-9 to 380 x 10-9. Visible light also has its own spectrum representing the seven colors: red, orange, yellow, green, blue, indigo, and violet. Applications of visible light include our sight, illumination, fiber optic communications, etc.
• Ultraviolet Rays: these are in the frequency range of 8 x 1014 Hz to 3 x 1016 Hz. Its wavelengths range from 380 x 10-9 m to 10 x 10-9 m. Ultraviolet rays are constantly blasted towards the earth by the sun. However, the Earth’s atmosphere blocks the majority of it from reaching the Earth’s surface. It is harmful to human skin. It is vastly used in medical and industrial processes.
• X-Rays: these are in the frequency range of 3 x 1016 to 1018. Wavelengths range from 10-9 m to 100 x 10-12 m. X-rays are used in viewing inner human tissue and bones.
• Gamma Rays: these are EMR with frequencies above 1018 Hz with wavelengths below 100 x 10-12. Gamma rays are very harmful to human tissue. However, in controlled doses, they are used to kill cancer cells.