1. Modern Physics Course Transition
Prelude to matter duality
Relativity (we’re trapped in 4D)
The Quantum World
Implications of the Quantum Reality
The Discovery Frontier

2. Incident report: Possible firmware problem + new base
“First, we cannot find any clicker responses for the last two questions of session 3 for your course. There isn't anything else we can do here and you will need to throw out the last 2 questions in Session 3 to be fair to the clicker users. It appears that the base got into a bad state that caused all clicker votes to no longer be recorded and we suspect that this may be related to a firmware problem. We are already working on an update to the Mac that will include base logging to allow us to better troubleshoot Mac incidents in the future. In the meantime, is it possible to get the firmware version of the base used for the problem session so we can continue to dig into the error? You can get the information using the Base Firmware Utilities app downloaded from iClicker.com (

3. Nuclear Physics Question
Kim Jong Un and nuclear bomb “mockup”

4. Nuclear Physics in PHYS274 (Fission or Fusion ?)
Layered Atomic Bomb
uses more thermonuclear fuel outside the atomic
core
Implosion Atomic Bomb uses conventional explosives to compress and ignite atomic fuel
Hydrogen Bomb
uses lots of hydrogen
fuel that the nearby
atomic core ignites
Boosted Atomic Bomb uses a bit of thermonuclear fuel inside the atomic core
Not clear what North Korea detonated. Maybe #2, a boosted atomic (fission) bomb. 3 25 1
1,000
Relative yields(compared to Hiroshima/Nagasaki, kilotons of TNT)

5. Diffraction part IV Quiz, Rayleigh criterion Crystal Diffraction
Holograms

6. A diffraction grating is composed of a single slit
Q7.1
A diffraction grating is composed of
a single slit
an array of many slits with varying widths and varying separations
an array of many slits with identical width and identical separation
an array of many slits with identical width but varying separations
C (many slits identical width and separation) 6

7. A diffraction grating is composed of a single slit
Q7.1
A diffraction grating is composed of
a single slit
an array of many slits with varying widths and varying separations
an array of many slits with identical width and identical separation
an array of many slits with identical width but varying separations
C (many slits identical width and separation) 7

8. a grating with very small number of slits
Q7.2
A diffraction grating can be used to distinguish 2 wavelengths that are very close to each other. This can be better accomplished with
a grating with very small number of slits
a grating with a large number of slits
Does not depend on the number of slits
B the resolving power is lambda/delta lambda = N m (as N increases the resolution improves). 8

9. a grating with very small number of slits
Q7.2
A diffraction grating can be used to distinguish 2 wavelengths that are very close to each other. This can be better accomplished with
a grating with very small number of slits
a grating with a large number of slits
Does not depend on the number of slits
B the resolving power is lambda/delta lambda = N m (as N increases the resolution improves).
N is the number of slits (note dimensions) 9

10. Q7.3
A 20 mm wide diffraction grating has 1,000 lines/mm. The first order diffraction is used to distinguish two wavelengths, λ1=500nm and λ2=500nm + Δλ . What is the minimum value of Δλ?
0.025nm
0.05nm
0.5nm
2.5nm
R=Lambda/Delta Lambda=N m, N is the number of slits. N =20mm x 1000 lines/mm=20000.
A) since 500nm/20000=0.025 nm 10

11. Q7.3
A 20 mm wide diffraction grating has 1,000 lines/mm. The first order diffraction is used to distinguish two wavelengths, λ1=500nm and λ2=500nm + Δλ . What is the minimum value of Δλ?
0.025nm
0.05nm
0.5nm
2.5nm
Δλ = 500nm/20,000
N = 20mm * 1000 lines/mm = 20,000
m = 1, λ ~500nm
R=Lambda/Delta Lambda=N m, N is the number of slits. N =20mm x 1000 lines/mm=20000.
A) since 500nm/20000=0.025 nm 11

12. Summary of Diffraction Limit (Rayleigh’s criterion)
Angular radius of the first dark ring in the circular diffraction pattern
Rayleigh criterion for the diffraction limit
3,4 barely “resolved”
3 and 4 fully resolved
Lord Rayleigh 1904 Nobel Prize in Physics
Idea: center of one diffraction pattern coincides with the first minimum of the other. (Note that D is the diameter of the aperture for a lens or telescope.) 12

13. Bigger telescope, better resolution
Because of diffraction, large-diameter telescopes, such as the VLA (Very Large Array) radio telescope in New Mexico below, give sharper images than small ones.
27 telescopes, 25m in diameter effective aperture 36 km !
What is the angular resolution?
What do you need to know?
20 GHz
Use c=f λ
Rayleigh criterion gives (λ=1.5cm, D=36 km)
5 x 10-7 rad
~0.1 arcseconds
About same as Hubble (optical) 13

14. Sites for the SKA (Square Kilometer Array)
The effective area will be 3000 km when completed (sites on every continent except South America) 14

15. Crystal Diffraction Basics
Can we observe crystal diffraction with visible or ultraviolet light ? (Hint: what is the typical spacing of the components of a crystal.)
Ans: No, for example the wavelength of visible light is nm, but the plane spacing in NaCl is 0.28nm.
UV is 100nm to 380nm so that won’t work either.
How can we observe crystal diffraction and understand the atomic structure of a crystal (or a protein) ?
Ans: use coherent x-rays 15

16. X-ray diffraction
When x rays pass through a crystal, the crystal behaves like a diffraction grating, causing x-ray diffraction. The figure below illustrates this phenomenon.
A version of this experiment is done at UH in PHYS481L. 16

17. A simple model of x-ray diffraction
The Bragg condition for constructive interference is 2d sinθ = mλ
The path difference is the due to the dimensions of the crystals (reflected x-rays have slightly different path lengths) 17

18. A simple model of x-ray diffraction
N.B. different from two slit interference
The Bragg condition for constructive interference is 2d sinθ = mλ 18

19. An example of holography
Photographs of a holographic image from two different angles, showing the changing perspective. 19

20. Fanciful holography What is the difference?
Still major technical problems
Can you identify the Star Wars Characters ? 20

21. Holography again
By using a beam splitter and mirrors, coherent laser light illuminates an object from different perspectives. Interference effects provide the depth that makes a three-dimensional image from two-dimensional views.
Invented by Dennis Gabor, 1971 Nobel Prize in Physics 21

22. Holography depends on interference and the wave nature of light
By using a beam splitter and mirrors, coherent laser light illuminates an object from different perspectives. Interference effects provide the depth that makes a three-dimensional image from two-dimensional views.
Invented by Dennis Gabor, 1971 Nobel Prize in Physics 22

23. Q7.4
The figures depict the situation of X-ray diffraction of crystals. What is the condition for constructive interference (i.e. to obtain a bright spot on the diffraction pattern)? D 23

24. Q7.4
The figures depict the situation of X-ray diffraction of crystals. What is the condition for constructive interference (i.e. to obtain a bright spot on the diffraction pattern)? D 24

25. Review Q7.4
The figures depict the situation of X-ray diffraction of crystals. What is the condition for constructive interference (i.e. to obtain a bright spot on the diffraction pattern)? D 25

26. Decrease D (the diameter of the hole) and increase the wavelength
Q7.5
Which of the following methods will decrease the angular spread of the central bright spot?
Decrease D (the diameter of the hole) and increase the wavelength
Increase D (the diameter of the hole) and decrease the wavelength
None of the above
B (sin\theta_1 = 1.22 Lambda/D) 26

27. Decrease D (the diameter of the hole) and increase the wavelength
Q7.5
Which of the following methods will decrease the angular spread of the central bright spot?
Decrease D (the diameter of the hole) and increase the wavelength
Increase D (the diameter of the hole) and decrease the wavelength
None of the above
B (sin\theta_1 = 1.22 Lambda/D) 27

28. Q7.6
Fig. a Fig. b
Fig. a & b are photographs of the same objects taken with different diameter apertures. Which photograph is taken with a larger aperture?
Fig. a
Fig. b
They are the same
B (recall Rayleigh criterion: sin\theta_1 =1.22 lambda/D) 28

29. Q7.6
Fig. a Fig. b
Fig. a & b are photographs of the same object taken with different diameter apertures. Which photograph is taken with a larger aperture?
Fig. a
Fig. b
The same
B (recall Rayleigh criterion: sin\theta_1 =1.22 lambda/D) 29

30. Michael Jackson “Hologram” at Billboard Music Awards
N.B. Does not work from all angles
This is Michael Jackson performing on stage after his death.
Star Wars
Not achieved 30

31. Goals for Chapter 36 (Diffraction)
To see how a sharp edge or an aperture affects light
To analyze single-slit diffraction and calculate the intensity of the light
To investigate the effect on light of many closely spaced slits
To learn how scientists use diffraction gratings (e.g. in astrophysics)
To see what x-ray diffraction tells us about crystals, proteins…
To learn how diffraction places limits on the resolution of a telescope
Holograms !
On Friday, start special relativity 31

32. Backup Slides Herring (“nishin” (鰊) in Japanese) 32
200 micron scale photo
Herring (“nishin” (鰊) in Japanese)
The color of butterfly wings is not from pigmentation (dull brown) but from interference in small structures on the wings 32