Diffraction+Lesson

__ LIGHT AND MATTER LESSON  __ __X-ray and optical diffraction crystalography__

Page by Adrian Boyarsky and Russell Bray
= = Materials NOTE: ALL PICTURES REFERENCED ON THIS PAGE CAN BE FOUND ON THIS WEBSITE __ Teacher Notes: __ __ Order of Activities: __ __ Background/Pre-requisites __ A previous diffraction unit should be completed in the use of interference (constructive and destructive) and a basic idea of unit cell structure.
 * Red Lasers
 * Green Lasers (if available)
 * Blue Laser (if available)
 * Powerpoint presentation from University of Wisconsin-Madison: []
 * ICE slides or transparency copies
 * CD, DVD, and Bluray
 * Prep time – 15minutes
 * Classtime- 2-3 hours
 * This lesson should coincide with a modeling unit in diffraction. It can be used as a paradigm activity to introduce the Fraunhover equation or used as an application of this knowledge. The order presented here will serve both purposes.
 * 1) Students will use the discovery slide to introduce basic diffraction patterns and how to interpret them.
 * 2) The Fraunhover equation (variation) will be introduced using observations from activity
 * 3) Students will compare the memory capacity of CD’s, DVD’s, and Blue-Rays. After students are able to derive the storage capabilities, the powerpoint can be used to show the physical diffrances between the media using high magnification.
 * 4) Students will use the unit cell slides and diffraction patterns to deduce the structure of different cells
 * 5) The optical diffraction should be compared to X-ray diffraction by showing a comparison of the technology used in each

 LIGHT AND MATTER: DIFFRACTION LESSON Student Notes Part 1 1. Setup the laser on a level surface. Have one group member hold the ICE discovery slide so that the ICE label is to the right as shown. Setup a whiteboard 1 to 2 meters away from the slide.  2. Shine the laser through the upper left array (A). Observe and sketch the pattern you observe. Move the beam to (C) and sketch the new pattern. (A) (C) What is the difference between pattern (A) and pattern (C) on the slide?

What is the difference between pattern (A) and pattern (C) on the whiteboard?

3. Do the same for pattern (B) and (D). Sketch the patterns below: (B) (D)

How do these patterns differ from those in step 2?

How are these patterns similar to the patterns in step 2?

4. Create a whiteboard showing your results and answers. Also look at the patterns for E – H. Based on what you have observed, make predictions on what we should observe on the whiteboard when we shine the light through each and put your predictions on a second whiteboard and be ready to discuss your predictions. (E)  (F) (G)   (H) 5. Observe the diffraction patterns for E – H. Sketch your observations below: (E)  (F)     (G)    (H)

Part 1 Review Questions: What is the diffraction pattern made by a set of horizontal slits?

What is the diffraction pattern made by a set of vertical slits?

How does the spacing of the slits affect the spacing of spots on the whiteboard?

What is the diffraction pattern of a square array of dots?

Record your conclusions in the space below and prepare a whiteboard to share your ideas.  Part 2 What is the spacing of tracks within a CD, DVD, or Blu-Ray? Using your group’s media and laser, devise a way to find the distance between tracks in the media. Record the wavelength of the laser: nm (1nm=1x10-9m) Make notes on your group’s procedure as you go. Include a sketch of your diffraction pattern and your measurements. You should end with a final answer in meters.
 * What is the general relationship between the spacing of dots on the slide and the spacing of dots in the square pattern on the board? **
 * What other variables in this experiment would affect this relationship? **

Prepare a whiteboard and share your method and results with the results.  Part 3 Diffraction can be used to determine the molecular structure of materials. In this activity, you will be able to see diffraction patterns of some common molecular structures. 1. Start by looking at slides (B) and (D). These both represent basic cubic structure. Sketch the diffraction patterns you see below: (B) (D)

What differences do you see in the diffraction pattern between (B) and (D)?

What must be different about the substances that would yield this result? What is the spacing of the atoms in the unit cell?

2. Look at slides (A) and (C). Sketch the diffraction patterns you see below: (A) (C)

How are these patterns different from (B) and (D)?

What type of unit cell structure yields these results?

How does the unit cell structure of (D) differ from (B)?

Name one material that would yield a diffraction pattern like (D)? Explain

Name one material that would yield a diffraction pattern like (B)? Explain

3. Finally, take the mystery material and shine the laser through it. What diffraction pattern do you see? What does this diffraction pattern tell about the structure of the molecule? Explain

 LIGHT AND MATTER: DIFFRACTION LESSON Teacher Notes Part 1 Student stations should be set up with a laser of some color, discovery slide, whiteboard with markers, and meter stick. 1. Setup the laser on a level surface. Have one group member hold the ICE discovery slide so that the ICE label is to the right as shown. Setup a whiteboard 1 to 2 meters away from the slide.

2. Shine the laser through the upper left array (A). Observe and sketch the pattern you observe. Move the beam to (C) and sketch the new pattern. Teacher should make sure students orient the discovery slide correctly. They should analyze a light beam moving through slits before moving to the dot patterns. A C     What is the difference between pattern (A) and pattern (C) on the slide? The spacing between the slits. Students should recognize that slits have a smaller opening in (C) What is the difference between pattern (A) and pattern (C) on the whiteboard? The spacing between diffracted dots is wider in (C) 3. Do the same for pattern (B) and (D). Sketch the patterns below: B D    How do these patterns differ from those in step 2? Students should realize that the slits being rotated also rotates the diffraction pattern. Horizontal slits lead to a vertical progression of dots. How are these patterns similar to the patterns in step 2? The spacing between the slits on the slides are the same and the spacing in the diffraction patterns is the same 4. Create a whiteboard showing your results and answers. Also look at the patterns for E – H. Based on what you have observed, make predictions on what we should observe on the whiteboard when we shine the light through each and put your predictions on a second whiteboard and be ready to discuss your predictions. Students should see the relationship between space between dots and how spread diffraction pattern should be. The powerpoint can be used to demonstrate this relationship. If groups are given different color lasers, the difference in the relationship should be explored; if not the powerpoint includes observations under blue and red laser light. Students should recognize that color is related to the wavelength of light and that smaller wavelengths yield smaller slit to dot spread ratios. 5. Observe the diffraction patterns for E – H. Sketch your observations below: E F    G  H

Part 1 Review Questions: What is the diffraction pattern made by a set of horizontal slits?

What is the diffraction pattern made by a set of vertical slits?

How does the spacing of the slits affect the spacing of spots on the whiteboard? As spacing of slits decreases, diffraction dot pattern spacing increases What is the diffraction pattern of a square array of dots?

Record your conclusions in the space below and prepare a whiteboard to share your ideas.  Part 2 What is the spacing of tracks within a CD, DVD, or Blu-Ray? Using your group’s media and laser, devise a way to find the distance between tracks in the media. Record the wavelength of the laser: nm (1nm=1x10-9m) Make notes on your group’s procedure as you go. Include a sketch of your diffraction pattern and your measurements. You should end with a final answer in meters. Photos courtesy of Philips Research. //Philips Research Password //, 2, January, 2000. [] Prepare a whiteboard and share your method and results with the results. Students should list measurements taken, calculations made, and a final answer with correct units along with any explanation  Part 3 Diffraction can be used to determine the molecular structure of materials. In this activity, you will be able to see diffraction patterns of some common molecular structures. 1. Start by looking at slides (B) and (D). These both represent basic cubic structure. Sketch the diffraction patterns you see below: B D
 * What is the general relationship between the spacing of dots on the slide and the spacing of dots in the square pattern on the board? As dots on slide get closer together, diffracted dots get wider. **
 * What other variables in this experiment would affect this relationship? Wavelengh, length from slide to board **

What differences do you see in the diffraction pattern between (B) and (D)? Spacing between interference patterns is larger in B than in D  What must be different about the substances that would yield this result? Atoms must be packed closer together in B.  What is the spacing of the atoms in each unit cell? Approximate Results: RED BEAM = GREEN BEAM= BLUE BEAM= 2. Look at slides (A) and (C). Sketch the diffraction patterns you see below: A C

How are these patterns different from (B) and (D)? The high intensity dots change from a + shape to a X shape. What type of unit cell structure yields these results? Body Centered Cubic How does the unit cell structure of (C) differ from (A)? The atom in the body of C is larger than in A, causing more space between the atoms on the adges of the cube Name one material that would yield a diffraction pattern like (A)? Explain

Name one material that would yield a diffraction pattern like (C)? Explain

3. Finally, take the mystery material and shine the laser through it. What diffraction pattern do you see?

What does this diffraction pattern tell about the structure of the molecule? Explain Answers here might vary. This is the pattern produced that led Watson and Crick to discover the structure of DNA. The X shape is the signature diffraction image of a helical structure. By calculating the distance between lines, the number of nucleotides per unit cell can be determined, which allowed them to determine the angle of incline in the helix. A closer examination of the slide shows the double helix structure like the one found in DNA. By measuring the angles between the arms of the cross in the diffraction pattern, one can calculate the period-to-amplitude ratio in the sine wave, or in the case of DNA, the helix. HLKJ: This group of arrays helps illustrate several of the more subtle features of the DNA diffraction pattern. In DNA the phosphorus atoms are part of the sugar-phosphate backbone of the DNA polymer, and, as the heaviest atoms, are the strongest scatterers of X-rays in the experiment. In the diffraction pattern of array K, a pattern of four diamonds is visible. The fact that the north and south diamonds are empty of diffraction intensity, and the east and west diamonds contain diffraction intensity, indicated that the sugar-phosphate backbone was on the outside of the DNA double helix, and the base pairs lie on the inside of the DNA molecule. Lastly, in array J, along with the sine waves of dots, as in array K, ten short horizontal lines have been added to the inside of the double sine waves. These ten horizontal lines represent the ten base pairs per period THAT lie on the inside of the DNA double helix. In the diffraction pattern of J, there are "blobs" (or groups of spots), of diffraction intensity at the top and bottom of the diffraction pattern. These "blobs" can also been seen in Franklin's original DNA diffraction image, and indicate the spacing of the base pairs within the DNA double helix. There are exactly ten base pairs per period of the DNA double helix. This can be confirmed by noting that the "blobs" of diffraction occur at the 10th layer line of the X-shaped cross.