How do electromagnetic waves travel?
Electromagnetic waves propagate through space as varying magnetic and electrical fields (hence, 'electromagnetic').
There are two main differences between sound waves and light waves. The first difference is in velocity. Sound waves travel through air at the speed of approximately 1,100 feet per second; light waves travel through air and empty space at a speed of approximately 186,000 miles per second.
The second difference is that sound is composed of longitudinal waves (alternate compressions and expansions of matter) and light is composed of transverse waves in an electromagnetic field.
Although both are forms of wave motion, sound requires a solid, liquid, or gaseous medium; whereas light travels through empty space. The denser the medium, the greater the speed of sound. The opposite is true of light. Light travels approximately one-third slower in water than in air.
Sound travels through all substances, but light cannot pass through opaque materials. From: http://electriciantraining.tpub.com/14182/css/Comparison-Of-Light-Waves-With-Sound-Waves-44.htm
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