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Ultrasounds and Scans

EM waves are transverse so the vibrations move at a 90° angle to the direction the wave is travelling. It has crests, the highest point of the wave, and troughs, the lowest point of the wave. 

Sound is longitudinal so the vibrations move in the same direction as the wave travels. There are compressions in the wave, an area of higher pressure where the particles of the material it is passing through are closer together, and rarefactions, an area of lower pressure where particles are more spread out. For example:

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The wavelength of the wave is…