|Why can't light go around corners? And why can
All waves exhibit similar properties, and both
light and sound are types of waves (although,
technically, light is a transverse wave and sound
is a longitudinal wave). One feature of waves,
known as diffraction, is that they can bend around
corners or obstacles. The degree of diffraction
increases with increasing wavelength.
Furthermore, the size of the obstacle(or opening
it is passing through) must be comparable to or
smaller than the wavelength of the waves. If the
wavelength is much smaller than the obstacle
(opening), there will not be much, if any,
diffraction. Since the wavelength of visible
light is on the order of 0.5 microns, or 0.0005
mm,light will only diffract when going through
very narrow openings. Sound waves, on the other
hand, have a wavelength on the order of 1 meter
and diffract very easily. This allows sound waves
to bend around corners.
The answer to this question has to do with the
fact that both light and sound are made up of
However, the waves which make up sound
are quite long - each wave is a foot long, about
the same length as waves you might see in the
water at the beach (the length of a wave is called
On the other hand, the waves
which make up the light we see are much much
smaller - about a million times smaller.
are about as small as the smallest thing you can
see under a very good microscope. Now it happens
that one of the things about waves is the
following: if they encounter an obstacle which is
smaller than their wavelength, the wave just kind
of wraps around the object and keeps on going.
This is why you can hide behind a big tree
trunk and the voices of people on the other side
of the tree will still reach you (because the long
waves of the sound wrap around the tree), but
light from their flash light won't (because the
short waves of the light can't wrap around such a
big object). Sound and light act similarly when
they reach a corner of a house - the sound waves
are long and kind of wrap around the corner and
then spread out from there, where as the very
short light waves can't bend around the
As you might have guessed already,
this means that light does wrap around very small
things (things smaller than a millionth of a
foot), and does bend a tiny tiny bit around
corners, but mostly this is so small it is
impossible to see with your eye.
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