WHAT IS NASA PHYSICS?
Forces and Motion
Conservation of Momentum & Energy
Temperature and Heat
Anticipation Guide 7
Intro to Modern Physics
The Ultraviolet Catastrophe
The Photoelectric Effect
Special Relativity (SR)
Distance and Time
May the Forces be with You
Modern Physics Notebook
Assessment Problems 7
The EMS is all the radiation that exists. The radiation that our eyes can see is called the visible spectrum. Other parts of the EMS occur outside this region and we must build special instruments to detect them. The EMS radiation (both visible and invisible) is characterized by wavelength and frequency. The broad range of radiation is grouped into general spectral regions based on their wavelength and frequency.
Students often come up with a mnemonic phrase to remember this sequence.One such phrase is: Rosa’s Mom Invited Very Ugly Xmas Guests. Here’s another one: A Radioactive Monkey is Very Interesting and eXtremely Goofy.
You can do better than these!The EMS is traditionally divided into the categories of:
In this chart the wavy line at top shows that wavelengths are short at the gamma ray end of the spectrum, and long at the radio end. The light blue wavelength arrow shows that and gives the lengths of some representative wavelengths in meters. You notice that all wavelengths except radio waves are shorter than a meter in length, in fact, many are shorter than a millionth of a meter. The bottom pictures show things that are about the size of the different wavelengths – from football fields to the nucleus of an atom.
Look at your microwave oven. When food is cooking in the oven, you can watch it by looking through the oven window. Just behind the window is a metal lattice with tiny holes that allow you to see the food. Why can visible light from the food make it to our eyes but the dangerous microwaves can’t?
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Answer: The microwave wavelength is too long.
Look at the EMS chart above to see that the wavelength of microwaves is around 1 m; they are too long to escape through the small holes in the metal lattice. Visible light is about a millionth of a meter in wavelength so light just whips through what are giant holes for their radiation.