Diffraction
Diffraction is the apparent ``bending''
of light waves around obstacles
in its path.
Diffraction of waves through a slit
This bending is due to Huygen's principle, which states that all
points along a wave front act as if they were point sources. Thus,
when a wave
comes against a barrier with a small opening, all but one of the
effective point
sources are blocked, and the light coming through the opening
behaves as a single point source, so that the light emerges in all
directions, instead of
just passing straight through the slit.
Note:
- For sizeable diffraction effects to occur the width of the opening
must be
of the same order or less than the wavelength of the light used.
- Diffraction limits the resolving power of microscopes and
other
magnifying devices. If the object being viewed is smaller than the
wavelength
of light used, then the light diffracts around the object, and
severely distorts the image. Thus microscopes using visible light
have a resolving power of only
about 600 nm
to about 10- 6m, but X-rays, whose wavelength is
about 0.1 nm ( 10- 10 m)
have a resolving power four orders of magnitude smaller.