1. Chapter 19 Diffraction and Interference of Light

2. Objectives • 19.1Relate 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

3. Objectives • 19.2Explain 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

4. Chapter 19: Wave model

5. Diffraction • Bending around an object. • Short Waves diffract less

6. Single Slit • Reminder: If the wave is too big, won’t fit through

7. 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

8. Usefulness of Young’s Double Slit Experiment • How we were able to determine the wavelengths of light • We’ll avoid the math for now

9. Diffraction Grating • Lots of slits, able to produce patterns like the double slit

10. Diffraction Patters • Double Slit • Wavelength of light = X (Distance between interference bands on screen) D (distance between slits) / L (Distance from slits to screen)

11. Diffraction Patterns • Single Slit • Single Slit Equation: X = (Lamda)(L) / W (Width)

12. CD: A very crude diffraction grating

13. 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