The Electromagnetic Spectrum

Learning Objectives

Define an electromagnetic wave.

List the main types of waves in the electromagnetic spectrum in order of wavelength.

Describe the relationship between wavelength, frequency, and energy in an EM wave.

Provide an example or use for each major type of EM wave.

Light and Beyond

Light is a form of energy that we can see. But the visible light our eyes can detect is just a tiny part of a much wider range of energy called the electromagnetic (EM) spectrum.

What is an Electromagnetic Wave?

An electromagnetic wave is a disturbance that involves oscillating electric and magnetic fields. Unlike sound waves, EM waves do not need a medium to travel. They can travel through the vacuum of empty space. This is how light from the Sun reaches Earth.

All electromagnetic waves travel at the same incredible speed in a vacuum: the speed of light, which is about 300,000 kilometers per second (186,000 miles per second).

The Regions of the EM Spectrum

The EM spectrum is the complete range of all types of EM waves, organized by their wavelength or frequency. Wavelength is the distance from the crest of one wave to the crest of the next. Frequency is the number of waves that pass a point each second.

Here are the main regions of the EM spectrum, listed in order from longest wavelength to shortest wavelength:

1.Radio Waves: Have the longest wavelengths and lowest frequencies.

Uses: Radio and television broadcasting, radar, cell phone communication.

2.Microwaves:

Uses: Microwave ovens (they are tuned to excite water molecules), radar, and satellite communication.

3.Infrared Radiation (IR):

Uses: We feel infrared as heat. It's used in thermal imaging cameras, night vision goggles, and remote controls.

4.Visible Light: The very narrow band of wavelengths that our eyes can see. The colors, from longest wavelength to shortest, are Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROY G BIV).

5.Ultraviolet (UV) Light:

Uses: UV radiation from the sun causes sunburn. It is also used in sterilizing equipment and by some insects to see flowers.

6.X-rays: Have very short wavelengths and high energy.

Uses: Medical imaging (they can pass through soft tissue but not bone), airport security scanners.

7.Gamma Rays: Have the shortest wavelengths, highest frequencies, and highest energy.

Uses: Emitted by radioactive materials and in nuclear reactions. Used in medicine to treat cancer.

Wavelength, Frequency, and Energy

There is a simple and important relationship between the properties of an EM wave:

As wavelength decreases, frequency increases.

As frequency increases, the energy of the wave increases.

This means that long-wavelength radio waves are very low-energy, while short-wavelength gamma rays are extremely high-energy and can be dangerous to living cells.

Key Terms

**Electromagnetic (EM) Spectrum: The complete range of electromagnetic waves placed in order of increasing frequency (and decreasing wavelength).
**Electromagnetic Wave: A transverse wave that involves the transfer of electric and magnetic energy and can travel through a vacuum.
**Wavelength: The distance between the crest of one wave and the crest of the next wave.
**Frequency: The number of waves that pass a given point in a certain amount of time.
**Speed of Light: The speed at which all electromagnetic waves travel in a vacuum, approximately 300,000 km/s.