Fraunhofer Diffraction - Single Slit

Introduction

• Fraunhofer diffraction occurs when light passes through a single slit.
• Observed using a spectroscope with a monochromatic light source.
• Diffraction pattern spreads out as the slit narrows, disappearing at a slit width equal or less than one wavelength of light.

Diffraction Mechanics

• Slit Width (a): The width of the single slit.
• Diffraction Direction: Focus on one direction where diffraction occurs towards point P.
• Path Difference (BN):
  • Waves from slit sides have a path difference.
  • Path difference BN = a sin(θ).
  • When BN = λ (wavelength), the light from top and bottom cancels out, resulting in a minimum at point P.
• Condition for Minima:
  • General condition: [ m \lambda = a \sin(\theta) ]
  • ( m ) is the order of the diffraction image (m = 1, 2, 3, ...).
  • Path difference corresponds to m wavelengths fitting into BN.

Intensity Distribution

• Intensity plotted against distance from the slit forms a distinct pattern.
• Pattern varies with changes in wavelength.

Wavelength Effects

• Pattern Variation:
  • Red light pattern is broader than blue due to longer wavelength.
• Visual representation highlights broader spread for longer wavelengths.

Additional Information

• A more detailed version is available in Word format on the Schoolphysics USB.