1. Physics for Scientists and Engineers II, Summer Semester 2009 1 Lecture 28: August 3 rd 2009 Physics for Scientists and Engineers II

2. Physics for Scientists and Engineers II, Summer Semester 2009 2 The Single Slit Diffraction Pattern (Fraunhofer Diffraction Patters) y1y1 y2y2 -y 1 -y 2

3. Physics for Scientists and Engineers II, Summer Semester 2009 3 The Single Slit Diffraction Minima Huygens Principle: Each part of the slit is a source of light waves. 1 2 3 1b 2b 3b Under these conditions: Ray 1 interferes Destructively with 1b, 2 with 2b, etc…

4. Physics for Scientists and Engineers II, Summer Semester 2009 4 The Single Slit Diffraction Minima Divide slit into 4 equal parts: Divide slit into 6 equal parts: Divide slit into 2m equal parts:

5. Physics for Scientists and Engineers II, Summer Semester 2009 5 Intensity Distribution of the Single-Slit Diffraction Pattern

6. Physics for Scientists and Engineers II, Summer Semester 2009 6 Intensity Distribution of the Single-Slit Diffraction Pattern

7. Physics for Scientists and Engineers II, Summer Semester 2009 7 Intensity Distribution of the Double-Slit Diffraction Pattern Double slit pattern – as discussed before Each of the two slits exhibits the single slit diffraction pattern

8. Physics for Scientists and Engineers II, Summer Semester 2009 8 Intensity Distribution of the Double-Slit Diffraction Pattern

9. Physics for Scientists and Engineers II, Summer Semester 2009 9 Suppressed Maxima in the Double Slit Pattern

10. Physics for Scientists and Engineers II, Summer Semester 2009 10 Resolution of Single Slit Apertures S1S1 S2S2 S1S1 S2S2 Unresolved center maxima for smaller angle. Just barely resolved center maxima (max. of S1 falls on first min. of S2. (Rayleigh’s criterion)

11. Physics for Scientists and Engineers II, Summer Semester 2009 11 Resolution of Single Slit Apertures S1S1 S2S2 Just barely resolved center maxima (max. of S1 falls on first min. of S2. (Rayleigh’s criterion)

12. Physics for Scientists and Engineers II, Summer Semester 2009 12 Resolution of Single Slit Apertures Example: Telescopes using mirrors of a certain diameter:  The larger the mirror, the smaller the limiting angle of resolution. (Critical in viewing close objects that are far away).

13. Physics for Scientists and Engineers II, Summer Semester 2009 13 The “Diffraction” (Interference) Grating Transmission Grating

14. Physics for Scientists and Engineers II, Summer Semester 2009 14 The “Diffraction” (Interference) Grating Reflection Grating

15. Physics for Scientists and Engineers II, Summer Semester 2009 15 The Spectrometer f Light source Telescope Eye Analyze the spectral lines of atoms (learn about electronic energy levels). Identify the composition of gases (e.g., what atoms are sending out light from a distant star (send light through spectrometer and look for “fingerprint” of atoms.

16. Physics for Scientists and Engineers II, Summer Semester 2009 16 X-Ray Diffraction

17. Physics for Scientists and Engineers II, Summer Semester 2009 17 Linearly Polarized Light y z x E B Linearly polarized light

18. Physics for Scientists and Engineers II, Summer Semester 2009 18 Unpolarized Light Unpolarized light (traveling out of the page) Is a superposition of many em waves that have electric fields polarized in different directions. Example: Emitted from an ordinary light bulb.

19. Physics for Scientists and Engineers II, Summer Semester 2009 19 Polarizing Light By Preferential Absorption Polaroid (a material with oriented long-chained molecules that selectively transmits light whose electric field is oriented along these molecules and absorbs light that has its E-field oriented perpendicular to these molecules. Polarized light

20. Physics for Scientists and Engineers II, Summer Semester 2009 20 Crossed Polarizers Second polarizer oriented the same as first:  All the polarized light passes through the Second polarizer. Polarized light

21. Physics for Scientists and Engineers II, Summer Semester 2009 21 Crossed Polarizers Second polarizer oriented perpendicular to first:  All the polarized light is absorbed in the second Polarizer.  No light passes through second polarizer. Polarized light

22. Physics for Scientists and Engineers II, Summer Semester 2009 22 Crossed Polarizers Second polarizer oriented at angle to first:  Only the component of E-field in direction of second polarizer gets through  Transmitted Intensity is proportional to E2. Polarized light

23. Physics for Scientists and Engineers II, Summer Semester 2009 23 Polarizing Light by Reflection incident reflected refracted

24. Physics for Scientists and Engineers II, Summer Semester 2009 24 Polarizing Light by Reflection incident Reflected light polarized refracted “Brewster Angle”