EWN - Electromagnetic Spectrum

Electromagnetic Spectrum

Introduction

Early experiments showed that light was a type of wave. Maxwell showed that it was, specifically, an electromagnetic wave. While most people think of light as consisting of just that which we can see (visible light), there is a broad range of frequencies of electromagnetic waves that extend well below and above what humans are capable of perceiving with their eyes. The full range of frequencies is organized into the electromagnetic spectrum.

There are several trends within the spectrum that you should take note of.

As you move from the radio to gamma ray end of the spectrum the frequency of the waves is increasing.
As you move from the radio to gamma ray end of the spectrum the wavelength of the waves is decreasing.
As you increase in frequency along the spectrum the waves are also increasing in energy.

The electromagnetic spectrum is usually shown organized from lowest frequency to highest frequency. The spectrum is divided into different sections or "bands" based on properties and common uses of that range of frequencies. From lowest to highest frequency the most common bands are: radio, microwave, infrared, visible, ultraviolet, x-rays, and gamma rays.

Radio: waves are commonly used for communication purposes. The number associated with your favorite FM radio station is an indication of the frequency of radio wave carrying that signal to you as measured in mega hertz, e.g. 94.1 would be 94.1 MHz.

Microwaves: are also used for communication, like cell phones and satellites, as well as heating food in your microwave oven.

Infrared: waves can transmit heat energy. That red heat lamp you may use for your pet or see keeping food warm at a restaurant, is an excellent source of infrared waves.

Visible light: waves make up the tiny portion of the entire spectrum that the human eye can perceive. The visible band begins with red light at a wavelength of about 750 nm and goes through violet light at a wavelength of about 400 nm. The colors of the rainbow, ROYGBIV, are the order of colors in the visible spectrum from lowest to highest frequency: red, orange, yellow, green, blue, indigo, and violet.

Ultraviolet: waves have energies high enough to sterilize bacteria and viruses and can therefore be used to disinfect. UV absorption from the Sun leads to the production of Vitamin D in humans. However, too much UV absorption can lead to sunburn or some forms of skin cancer.

X-rays: have high energies that allow them to easily pass through the human body, which makes them useful for creating images of denser internal structures like bones.

Gamma rays: are the highest frequency, shortest wavelength, and highest energy waves. They are primarily created in nuclear reactions, like the process that powers the Sun, but can also be created by other means such as radioactive decay.

This video shows how various bands of the electromagnetic spectrum are at work around us all of the time.

Speed of Light

In the electromagnet spectrum you should have noticed an inverse relationship between the frequency and wavelength as you move across. This is shown mathematically in the relation between the speed of light, frequency, and wavelength.

The speed of light in a vacuum, c is constant for all forms of electromagnetic waves. This leads to an inverse relationship between frequency and wavelength. Effectively, if you are given either the frequency or wavelength of a given EM wave, you can directly calculate the other for that wave.

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