2. Diffraction Monochromatic light Polychromatic light
the spreading of a wave around the
edge of a barrier or through an opening
Monochromatic light
consists of only one color (wavelength).
Polychromatic light
consists of more than one color (wavelength).

3. “Each point on a wavefront acts as a new source of disturbance.”
Huygen’s Principle
is used to explain diffraction.
“Each point on a wavefront acts
as a new source of disturbance.”

4. Click here to read about
Christiaan Huygens.
Click here and here to view simulations
of Huygen’s Principle.
Huygen’s Principle can be used to explain
reflection and refraction, as shown here.

5. x d l = L Young’s Double Slit Interference x d x L
l is the wavelength of light
d is the distance between slits
x is the distance from the central bright band
to the first order bright line
L is the distance from slits to screen

6. Click here and
here to view
simulations
of double slit
interference.
Notice changes in the interference pattern
as each variable changes.

7. Click here,
here, here,
and here to
view single slit
interference
simulations.
Notice how the pattern changes as each
variable is manipulated.

8. Single Slit Interference Characteristics
central bright band
pattern spreads out as wavelength increases
pattern spreads out as distance to screen increases
pattern spreads out as distance between slits decreases
Similar results occur with a narrow single slit.
Single Slit Interference
Characteristics
central bright band
narrower slit produces wider central band
larger wavelength gives wider pattern

9. Diffraction Gratings series of many slits etched on film
Diffraction gratings (or replica gratings)
will separate light into its component colors
through diffraction and interference.
They are often used to identify the
component colors of polychromatic light.

10. Click here to view a
simulation of a
diffraction grating.
Notice the changes in the diffraction
pattern as the variables are manipulated.

11. Thin Film Interference
The color spectrum seen in a soap bubble, or
any thin film, results from the interference
of the reflections of light from the
front and back surfaces of the film.
The colors seen depend on the thickness of the
film. The light most strongly reflected has a
wavelength such that the film thickness is an
odd multiple of l/4. Other wavelengths will
suffer partial or total destructive interference.