Download 10.2 Diffraction Notes

Chapter 10.2
Wave
Interference and
Diffraction
• Interference occurs when
light from one source
mixes with light from
another source.
• Diffraction occurs when
light bends around the
edge of an obstacle.
• The study of light interference
and light diffraction is called
physical optics.
• The superposition principle
says that the amplitude of a
wave is the sum of the
amplitudes of both waves
when they meet in
interference.
• If waves are in phase, there is
a reinforcement of amplitudes.
This is called constructive
interference.
• In waves that are not in phase,
there is a partial or complete
cancellation of the amplitudes.
This is called destructive
interference.
• If the amplitude of wave 1 is 40
and the amplitude of wave 2 is
60, what is the total amplitude is
the waves are in phase?
• In Phase so add; 40+60 = 100
• If the waves above are out of
phase, what is the total
amplitude?
• Out of Phase so subtract;
60 – 40 = 20
• Destructive interference is difficult
to accomplish since most natural
sources of light are incoherent which means they emit light
waves randomly.
• It is much easier to observe light
if the phases of the waves have a
fixed pattern. This is called
coherent.
• A light that has a single
wavelength is called
Monochromatic.
• White light from a bulb
or from the sun has 7
wavelengths.
• If we place a monochromatic
light, such as a laser so that
the light goes through a single
slit, the light is diffracted.
• The diffraction from the light
will cause a pattern of
constructive and destructive
interference which will be seen
as dark and light bands.
• A diffraction grating is an
optical device that uses a
large number of slits to
transmit or reflect light to
form a pattern.
• Gratings are made by
scratching very fine lines in
a glass with a diamond.
Diffraction Glasses
• A diffraction grating allows
us to see the colors
separated from white light.
• An optical instrument that
uses a diffraction grating to
measure wavelengths is
called a grating
spectrometer.
3D Glasses
•Put on your
glasses!