Electromagnetic Spectrum

The electromagnetic spectrum includes all electromagnetic waves with various wavelengths and frequencies. Electromagnetic waves are waves that are capable of traveling through a vacuum. They don’t need a medium to transport their energy.

Since electromagnetic waves are cased by vibrating charges, they have both an electric field component and magnetic field component. Both components are perpendicular to the direction of motion of the wave. See Figure below.

Figure (EM waves)

In the figure, the horizontal arrow indicates the direction in which the wave is traveling or the direction of its velocity. Then the electric field, \vec E and magnetic field \vec B are perpendicular to the arrow.

The electromagnetic waves are arranged in the spectrum based on their wavelengths and frequencies. Below is a figure of the electromagnetic spectrum

Figure (Electromagnetic Spectrum)

The waves with longer wavelengths have lower frequencies and are found at the far-left side of the spectrum. The waves with shorter wavelengths have higher frequencies and are located at the far-right corner of the spectrum. The frequency of the wave also determines its characteristic. The wave with higher frequency is more energetic and wave with lower frequency possesses lesser energy.

Each wave in the spectrum is very much important. Radio waves are responsible for the global communication system. AM radio uses waves with frequencies ranging from 5.4 x 105 Hz to 1.6 x 106 Hz. FM radio uses waves with frequencies from 8.8 x 107 Hz to 1.08 x 108 Hz. Radio waves have the longest wavelengths but lower frequencies.

The next part of the spectrum are the microwaves. These are also used for communication such as in mobile phones and wireless networks. Weather radar at frequencies about 3.0 x 109 Hz is another application of microwave.

Infrared radiation is used in some cameras. Cameras have devices which emits a beam of infrared and through this, they are able to determine the distance from the subject and adjust the focus automatically by analyzing the infrared radiation reflected from the subject.

X-rays are very much important in the medical industry. These waves are able to penetrate through flesh which is useful in determining inner problems or conditions in the body.

Gamma rays are helpful also in medical field such as in killing cancer cells. Gamma rays have the shortest wavelengths but highest frequencies.

A very small part at the middle of the spectrum is the only part that can be detected by our eyes, this portion is called as the visible light. The visible light spectrum is composed of waves of different colors with wavelengths that ranges from 750 nanometers to 380 nanometers. These colors are red (R), orange (O), yellow (Y), green (G), blue (B), and violet (V) abbreviated as ROYGBIV. The table below contains the range of the wavelengths of each color wave of the visible light.

 Visible Light Wavelength (nanometer, nm) Red 620 - 750 Orange 590 - 620 Yellow 570 - 590 Green 495 - 570 Blue 450 - 495 Violet 380 - 450

Although the electromagnetic waves in the spectrum have different frequencies and wavelengths, they all have the same speed – the speed of light which is equal to approximately 3.0 x 108 m/s. The relationship $$c = \lambda f$$ is true to all types of electromagnetic waves.