Diffraction
Describe the behavior of a wave and the diffraction pattern resulting from a wave passing through a single opening.
- Diffraction is the spreading of a wave around the edges of an obstacle or through an opening.
- Diffraction is most pronounced when the size of the opening is comparable to the wavelength of the wave.
- Diffraction of multiple wavefronts through a single opening leads to observable interference patterns.
- Diffraction is commonly demonstrated by monochromatic light of wavelength λ incident on a narrow opening of width a that is a distance L from a screen.
- Constructive and destructive interference of multiple wavefronts originating from the opening will result in bright and dark bands on the screen.
- The amount of interference between two wavefronts depends on the path length difference ΔD of the wavefronts.
- The path length difference ΔD can be described in terms of the opening width a and the angle θ between the direction of propagation of the wavefront and the normal to the opening by the equation:
- For small angles, where θ < 10°, the small angle approximation can be used to relate λ, a and L to ymin, the distance from the middle of the central bright fringe to the mth order of minimum brightness on the screen. Relevant equation:
- The diffraction pattern produced by a wave passing through an opening depends on the shape of the opening.
- Visual representations of single-slit diffraction patterns are useful in determining the physical properties of the slit and the interacting waves.