 Electromagnetic Radiation The universe is made up of matter and energy. Matter is the stuff that we can touch and feel. Energy is the capacity to move matter or supply heat. One form of energy is light. Light is made up of waves in the electric and magnetic fields of the universe. Since light is a wave, it can be characterized by either a wavelength or frequency. Wavelength, represented by the Greek letter lambda, is the distance between two successive peaks in a wave. The unit of a wavelength is meters. Though for visible light, the wavelength is so small it is measured in micrometers or nanometers. Frequency is the number of wavelengths passing through a fixed point in time. Units for frequency are hertz. One hertz is one cycle per second. In this example, we calculate frequency by counting how many wavelengths pass through per second. Both wavelength and frequency are related to the speed of light by the following equation. C equals frequency times wavelength, where C is the speed of light. Rearranging this equation, wavelength equals the speed of light divided by frequency. As frequency gets larger, the wavelength must get smaller. They are inversely related. What is the frequency of blue light with a wavelength of 450 nanometers? We need to use C equals frequency times wavelength. Rearranging this equation, we have frequency equals the speed of light divided by wavelength. Since light can have a variety of wavelengths, there are different types of light. Although you may not realize it, you are actually familiar with most common types of light. X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. These types of light vary from each other by their frequency and wavelength. If you could see radio waves, their wavelengths would range from the width of a baseball to the length of a soccer field, or longer. The electromagnetic spectrum encompasses all types of light. Light visible to humans ranges from 0.4 micrometers to 0.7 micrometers. This wavelength range encompasses all of the colors of the rainbow. Let's do a quick review. See if you know the correct location in the electromagnetic spectrum for each example. Radio wave. A radio wave has a longer wavelength than visible light. X-ray. An X-ray has a shorter wavelength than visible light. Infrared radiation. Infrared radiation has a longer wavelength than visible light. Gamma rays. Gamma rays have a shorter wavelength than visible light. Microwaves. Microwaves have a longer wavelength than visible light. ultraviolet radiation. Ultraviolet radiation has a shorter wavelength than visible light. Congratulations! You have completed this activity, electromagnetic radiation.