Chapter 36

1. Chapter 36 Diffraction (cont.)

2. A diffraction grating is an array of a large number of slits having the same width and equal spacing. (See Figure 36.16 at the right.) The diffraction grating

3. A diffraction grating can be used to disperse light into a spectrum. • The greater the number of slits, the better the resolution. • Figure 36.18(a) below shows our sun in visible light, and in (b) dispersed into a spectrum by a diffraction grating. Grating spectrographs

4. Q36.5 Consider two diffraction gratings. One grating has 100 lines/mm, and the other one has 200 lines/mm. Both gratings are illuminated with a beam of the same monochromatic light. Which grating produces the greater dispersion? • The dispersion cannot be determined without additional information • The grating with 100 lines/mm produces the greater dispersion. • C. Both gratings produce the same dispersion. • D. The grating with 200 lines/mm produces the greater dispersion.

5. A36.5 Consider two diffraction gratings. One grating has 100 lines/mm, and the other one has 200 lines/mm. Both gratings are illuminated with a beam of the same monochromatic light. Which grating produces the greater dispersion? • The dispersion cannot be determined without additional information • The grating with 100 lines/mm produces the greater dispersion. • C. Both gratings produce the same dispersion. • D. The grating with 200 lines/mm produces the greater dispersion.

6. When x rays pass through a crystal, the crystal behaves like a diffraction grating, causing x-ray diffraction. Figure 36.20 below illustrates this phenomenon. X-ray diffraction

7. Constructive interference is essentially the reason the angle of reflection equals the angle of incidence. • The Bragg condition for constructive interference is 2d sin = m. A simple model of x-ray diffraction

8. An aperture of any shape forms a diffraction pattern. • Figures 36.25 and 36.26 below illustrate diffraction by a circular aperture. The airy disk is the central bright spot. • The first dark ring occurs at an angle given by sin1 = 1.22 /D. Circular apertures

9. Diffraction limits the resolution of optical equipment, such as telescopes. • The larger the aperture, the better the resolution. Figure 36.27 (right) illustrates this effect. Diffraction and image formation

10. Because of diffraction, large-diameter telescopes, such as the VLA radio telescope below, give sharper images than small ones. Bigger telescope, better resolution

11. Q36.6 You use a telescope lens to form an image of two closely spaced, distant stars. Which of the following will increase the resolving power? A. Use a filter so that only the blue light from the stars enters the lens. B. Use a filter so that only the red light from the stars enters the lens. C. Use a lens of smaller diameter. D. more than one of the above

12. A36.6 You use a telescope lens to form an image of two closely spaced, distant stars. Which of the following will increase the resolving power? A. Use a filter so that only the blue light from the stars enters the lens. B. Use a filter so that only the red light from the stars enters the lens. C. Use a lens of smaller diameter. D. more than one of the above

13. 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. Figure 36.28 below illustrates this process. What is holography?

14. Initially an interference pattern is created in film, when light shines from behind on that film, it recreates the original image. How does holography work?

15. Figure 36.32 below shows photographs of a holographic image from two different angles, showing the changing perspective. An example of holography