Peoples Physics Concepts

16.8. Diffraction http://www.ck12.org

16.8 Diffraction

• Explain the diffraction of light and the interference patterns that are produced through constructive and
  destructive interference of the waves.


• Calculate diffraction pattern spacing or work backwards to calculate the wavelength of light emitted.

Students will learn about diffraction of light and the interference patterns that are produced through constructive

and destructive interference of the waves. Students will also learn to calculate diffraction pattern spacing or work

backwards to calculate the wavelength of light emitted.

Key Equations

mλ=dsinθ

Double slit interference maxima.mis the order of the interference maximum in question,dis the distance between

slits. andθis the angular position of the maximum.

mλ=dsinθ

Single slit interference maxima.mandθare defined as above anddis the width of the slit.

mλ=dsinθ

Diffraction grating interference maxima.mandθare defined as above anddis the distance between the lines on

the grating.

mλ= 2 nd

Thin film interference:nis the index of refraction of the film,dis the thickness of the film, andmis an integer. In

the film interference, there is aλ/2 delay (phase change) if the light is reflected from an object with an index of

refraction greater than that of the incident material.

1

f

=

1

d 0

+

1

di

Guidance

• Waves are characterized by their ability to constructively and destructivelyinterfere. Light waves which
  interfere with themselves after interaction with a small aperture or target are said todiffract.


• Light creates interference patterns when passing through holes (“slits”) in an obstruction such as paper or the
  surface of a CD, or when passing through a thin film such as soap.