Transcript Conference Management

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
www.MetrologyCareers.com
PRESENTING
the
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
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
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
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
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
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
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
Interference and light
Light exhibits constructive and destructive interference
Incoming light
Dark
Band
Bright
Band
Dark
Band
NCSL INTERNATIONAL
SERVING THE WORLD OF
MEASUREMENT SINCE 1961
Reflected light
Michelson’s interferometer
NCSL INTERNATIONAL
SERVING THE WORLD OF
MEASUREMENT SINCE 1961
The LASER
NCSL INTERNATIONAL
SERVING THE WORLD OF
MEASUREMENT SINCE 1961
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
Mirror
(fixed)
NCSL INTERNATIONAL
SERVING THE WORLD OF
Michelson interferometer with laser
NCSL INTERNATIONAL
SERVING THE WORLD OF
MEASUREMENT SINCE 1961
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
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