Which of the following does not belong in the electromagnetic spectrum? a. X-ray b. Sound c. Infrared ray d. Radio waves 

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Choice "B," sound, does not belong in the electromagnetic spectrum.  The full electromagnetic spectrum contains all of the various wavelengths and frequencies of electromagnetic radiation.  Within the spectrum, specific wavelengths and frequencies are divided up into groups.  The groups of electromagnetic radiation are radio waves, microwaves, infrared waves, visible light waves, ultraviolet waves, x-ray waves, and gamma waves.  I have listed those seven types of electromagnetic radiation in increasing energy.  

Sound wave energy is distinctly different than electromagnetic wave energy.  An electromagnetic wave is a transverse wave while sound is a longitudinal (compression) wave.  Secondly, sound waves need a medium to travel through.  On the other hand, electromagnetic waves do not need to travel through a medium.  They can travel through a medium, but they don't need the medium.  

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