Short Notes - Electromagnetic Spectrum | Wave & Optics for PAT PDF Download

 Page 1


Notes: Electromagnetic Spectrum 
 
The electromagnetic spectrum is more familiar to you than you might think. The 
microwave you use to heat your food and the cell phones you use are part of the 
Electromagnetic Spectrum. The light that our eyes can see is also part of the 
electromagnetic spectrum. This visible part of the electromagnetic spectrum consists 
of the colors that we see in a rainbow - from reds and oranges, through blues and 
purples. 
 
Did you know that electromagnetic waves can not only be described by their 
wavelength, but also by their energy and frequency? All three of these things are 
related to each other mathematically. This means that it is correct to talk about the 
energy of an X-ray or the wavelength of a microwave or the frequency of a radio 
wave. The electromagnetic 
spectrum includes, from longest 
wavelength to shortest: radio 
waves, microwaves, infrared, 
optical, ultraviolet, X-rays, and 
gamma-rays.  
 
Each of these colors actually 
corresponds to a different 
wavelength of light.  
Electromagnetic waves are formed when an electric field couples with a magnetic 
field.  The magnetic and electric fields of an electromagnetic wave are perpendicular 
to each other and to the direction of the wave. James Clerk Maxwell and Heinrich 
Hertz are the two scientists who studied how electromagnetic waves are formed and 
how fast they travel.  
 
Radio waves have the longest wavelength in the electromagnetic spectrum. These 
waves carry the news, ball games, and music you listen to on the radio. They also 
carry signals to television sets and cellular phones.  
 
Microwaves have shorter wavelengths than radio waves, which heat the food we eat. 
They are also used for radar images, like the Doppler radar used in weather forecasts.  
 
Page 2


Notes: Electromagnetic Spectrum 
 
The electromagnetic spectrum is more familiar to you than you might think. The 
microwave you use to heat your food and the cell phones you use are part of the 
Electromagnetic Spectrum. The light that our eyes can see is also part of the 
electromagnetic spectrum. This visible part of the electromagnetic spectrum consists 
of the colors that we see in a rainbow - from reds and oranges, through blues and 
purples. 
 
Did you know that electromagnetic waves can not only be described by their 
wavelength, but also by their energy and frequency? All three of these things are 
related to each other mathematically. This means that it is correct to talk about the 
energy of an X-ray or the wavelength of a microwave or the frequency of a radio 
wave. The electromagnetic 
spectrum includes, from longest 
wavelength to shortest: radio 
waves, microwaves, infrared, 
optical, ultraviolet, X-rays, and 
gamma-rays.  
 
Each of these colors actually 
corresponds to a different 
wavelength of light.  
Electromagnetic waves are formed when an electric field couples with a magnetic 
field.  The magnetic and electric fields of an electromagnetic wave are perpendicular 
to each other and to the direction of the wave. James Clerk Maxwell and Heinrich 
Hertz are the two scientists who studied how electromagnetic waves are formed and 
how fast they travel.  
 
Radio waves have the longest wavelength in the electromagnetic spectrum. These 
waves carry the news, ball games, and music you listen to on the radio. They also 
carry signals to television sets and cellular phones.  
 
Microwaves have shorter wavelengths than radio waves, which heat the food we eat. 
They are also used for radar images, like the Doppler radar used in weather forecasts.  
 
There are infrared waves with long wavelengths and short wavelengths. Infrared 
waves with long wavelengths are different from infrared waves with short 
wavelengths. Infrared waves with long wavelengths can be detected as heat. Your 
radiator or heater gives off these long infrared waves. We call these thermal infrared 
or far infrared waves. The sun gives off infrared waves with shorter wavelengths. 
Plants reflect these waves, also known as near infrared waves.  
 
Visible light waves are the only electromagnetic waves we can see. We see these 
waves as the colors of the rainbow. Each color has a different wavelength. Red has 
the longest wavelength and violet has the shortest wavelength. These waves combine 
to make white light.  
 
Ultraviolet waves have wavelengths shorter than visible light waves. These waves 
are invisible to the human eye, but some insects can see them. Of the sun's light, the 
ultraviolet waves are responsible for causing our sunburns.  
 
X-Rays: As wavelengths get smaller, the waves have more energy. X-Rays have 
smaller wavelengths and therefore more energy than the ultraviolet waves. X-Rays 
are so powerful that they pass easily through the skin allowing doctors to look at our 
bones.  
 
Gamma Rays have the smallest wavelength and the most energy of the waves in the 
electromagnetic spectrum. These waves are generated by radioactive atoms and in 
nuclear explosions. Gamma rays can kill living cells, but doctors can use gamma rays 
to kill diseased cells.