Diffraction and Interference

1
Diffraction and Interference

• Diffraction
• Huygens Principle
• Diffraction Lab

2
Light

• Has wave properties.
• Can diffract.
• Can constructively or destructively interfere.

3
Wave Fronts

• Lines that are perpendicular to the motion of the
  wave.
• Indicate the location of the crests in the waves
  that are traveling together.

4
Huygens Principle

• Wave fronts are made up of tinier wave fronts.
• Every point on any wave front is a new source for
  a secondary wave front.

5
Huygens Principle

• You can explain reflection and refraction using
  Huygens Principle.

http//www.microscopy.fsu.edu/primer/java/reflecti
on/huygens/
6
Huygens Principle

• As the straight waves passed through a narrow
  hole, they spread out in a circular pattern.
• Giving proof to the fact that every point on a
  wave front is a new source for a new set of
  wavelets.

http//www.ngsir.netfirms.com/englishhtm/Diffracti
on.htm
7
Diffraction

• Any bending of a wave around an obstacle or edges
  of an opening by means other than reflection or
  refraction.

8
Diffraction
Demo

• The amount of diffraction (bending) depends on
  the size of the wavelength compared with the size
  of the obstruction.
• The longer the wavelength is compared to the
  obstruction, the greater the diffraction.

9
Is Diffraction a Good Thing?

• Why would we ever want waves to bend past an
  obstruction?

10
Is Diffraction a Good Thing?

• Long AM radio waves can diffract around hills and
  buildings and can be received better in more
  places than short waves that dont diffract as
  much.

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Is Diffraction a Good Thing?

• Diffraction is bad when we want to see very small
  objects with microscopes.
• If the size of the small object is the same as
  the wavelength of light, the image will be
  blurred by diffraction.

12
Diffraction Lab