The following text gives a good overview of the differences and
similarities of sound and light.
"Many things in nature wiggle and jiggle," says Paul Hewitt in his
lucid book, Conceptual Physics.
"We call a wiggle in time a vibration and a wiggle in space and time a
wave." A wave cannot exist in one place but must extend from one place
to another, like ripples spreading out from a dropped pebble in a
lake. Similarly, a vibration cannot exist in one instant but needs
time to move to and fro, just as a plucked guitar string.
Light and sound are both vibrations that travel through space as
waves. They are, however, different.
Sound is a vibration of some medium that it travels through, like air
or water. Sound vibrations travel through air by compressing the air,
then rarefying the air, compressing the air, then rarefying... "If
there is no medium to vibrate," says Hewitt, "then no sound is
Light is a vibration of magnetic and electric fields ? a vibration of pure energy.
As you know, light waves can pass through many media: air, water,
glass, to name a few. But they do not need any medium. Sunlight,
moonlight, and starlight pass through the vacuum of outer space to
The source of all waves is something vibrating. The vibrating prongs
of a tuning fork generate a sound. Vibrating electrons in an atom
generate light. The basic difference between sound and light travel is
that sound requires an intervening substance to change and impose a
wave pattern on. Whereas light does not. Sound travel is motion; light
travel is radiation.
"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."
Search terms used:
Light Sound Difference
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