Chapter 19 Diffraction and Interference of Light
Objectives
• 19.1 Relate the diffraction of light to its wave characteristics
• 19.1 Explain how light falling on two closely spaced slits produces and interference pattern and use measurements to calculate wavelengths of light
• 19.1 Apply geometrical models to explain single slit diffraction and two slit interference patterns
Objectives
• 19.2 Explain how diffraction gratings form interference patterns and how they are used in grating spectrometers
• 19.2 Discuss how diffraction limits the ability of a lens to distinguish two closely spaced objects
Chapter 19: Wave model
Diffraction
• Bending around an object.
• Short Waves diffract less
Single Slit
• Reminder: If the wave is too big, won’t fit through
Vocabulary
• Interference pattern: Produced by overlapping of waves (areas of dark and intense light)
• Monochromatic: One wavelength of light• Coherent Waves: Wavelengths where crests
and troughs line up exactly
Usefulness of Young’s Double Slit Experiment
• How we were able to determine the wavelengths of light
• We’ll avoid the math for now
Diffraction Grating
• Lots of slits, able to produce patterns like the double slit
Diffraction Patters
• Double Slit
• Wavelength of light = X (Distance between interference bands on screen) D (distance between slits) / L (Distance from slits to screen)
lxd
Diffraction Patterns
• Single Slit
• Single Slit Equation: X = (Lamda)(L) / W (Width)
wlx
CD: A very crude diffraction grating
Astronomy Connection
• Light from telescopes enters through a tiny opening which ends up diffracting the light just a bit. If two stars are too close, you may not be able to tell if there is one or two
• The Rayleigh criterion for resolution