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Notes to the presenter

Notes to the presenter. This is an interactive presentation best done for a small group (15-20 maximum) Practice setting up the interferometer first, so you know how to do it. With practice, you can set it up in 5-10 minutes Total talk & demo can be done in 30-50 minutes

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Notes to the presenter

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  1. Notes to the presenter This is an interactive presentation best done for a small group (15-20 maximum) Practice setting up the interferometer first, so you know how to do it. With practice, you can set it up in 5-10 minutes Total talk & demo can be done in 30-50 minutes Participants should be encouraged to interact with the interferometer (which is why small groups work better) Don’t forget to turn in an ambassador outreach form! NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  2. www.MetrologyCareers.com NCSLI Michelson Interferometer in a Pizza Box! PRESENTING the

  3. Objectives You will learn about The roots of the metric system The definition of the meter Albert Michelson’s contribution to optics Principles of interferometry The geometry of the Michelson interferometer And you will interact with a working interferometer NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  4. Origins of the metric system • Prior to the French revolution, each region in France had its own standards • Different “yard” units for textiles (toise) • Different “bushel” units for grain • Different “pint” measures for beer • Idea of rationalizing units from 1670: Abbé Mouton proposes 1 minute of arc of the circumference of the earth as the primary standard of length; decimal divisions NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  5. More on the history of the meter • Other proposals (including Thomas Jefferson) based on the period of a pendulum; also proposals to use base 12 divisions • During the revolution (1780s-1790s), the French Academy of Sciences is commissioned to reform units • Meter: 1 part in 10,000,000 of the meridian (longitude line) from the North Pole to the Equator, passing through Paris NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  6. The early metric system 1 meter (1×10-7 of the earth quadrant) Area and volume derived from the meter Mass derived from volume: 1 gram = mass of water (at 0°C) in a volume of 1 cm3 Metric system not in widespread use until 1875 (May 20, 1875—signing of the Convention of the Meter) meter is based on the Platinum-Iridium meter at BIPM in Paris; kilogram based on the international prototype in Paris; each signing nation has copies NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  7. The meter in the US 1875: US signs the Convention of the Meter 1890: US receives K-4 and K-20 (kilogram standards) and meter 21 and 27 1893: T. C. Mendenhall, Superintendent of Weights & Measures in the US orders the adoption of the international prototype meter and kilogram as US standards. NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  8. Albert A. Michelson 1852-1931 Grew up in Northern California & West Nevada Appointed to US Naval Academy; returned as an instructor, then, to Case School of Applied Science, Clark University, and finally University of Chicago Did experiments to measure the speed of light, and also the Michelson-Morley experiment to determine the speed of travel of earth in the “aether” (1887) Visited BIPM to set up interferometers for measuring the meter bars! NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  9. The 1907 Nobel Prize in Physics The Royal Academy of Sciences has decided to award this year's Nobel Prize for Physics to Professor Albert A. Michelson of Chicago, for his optical precision instruments and the research which he has carried out with their help in the fields of precision metrology and spectroscopy. NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  10. Interference and light Incoming light Reflected light Dark Band Bright Band Dark Band Light exhibits constructive and destructive interference NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  11. Michelson’s interferometer NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  12. The LASER NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  13. Laser interferometer • Laser light is: • Monochromatic (all the same wavelength) • Coherent (all the “peaks” and “valleys” are in phase with each other) DETECTOR Beamsplitter Mirror (moving) LASER SOURCE beamsplitter Mirror (fixed) NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  14. Michelson interferometer with laser NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  15. Demo time! • In 1960, the meter was redefined to Krypton light wavelength • In 1983, the meter was redefined to be the distance traveled by light (in a vacuum) in 1/299 792 458 second • c ≡ 299 792 458 m/s NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

  16. For more information www.metrologycareers.com www.ncsli.org www.bipm.org NBS SP447 (from www.nist.gov) American Institute of Physics (www.aip.org) NCSL INTERNATIONAL SERVING THE WORLD OF MEASUREMENT SINCE 1961

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