Brownian Motion: Measuring Avogadro’s Constant (Within a Few Percent) For \$70 Beth Parks

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# Brownian Motion: Measuring Avogadro’s Constant (Within a Few Percent) For \$70 Beth Parks - PowerPoint PPT Presentation

Brownian Motion: Measuring Avogadro’s Constant (Within a Few Percent) For \$70 Beth Parks Rebecca Metzler Colgate University. Why Brownian Motion? Historically important: Einstein’s 1905 paper Important in practice: led to accurate measurement of Avogadro’s number

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Brownian Motion:

Measuring Avogadro’s Constant (Within a Few Percent)

For \$70

Beth Parks

Rebecca Metzler

Colgate University

Why Brownian Motion?

• Historically important: Einstein’s 1905 paper
• Important in practice: led to accurate measurement of Avogadro’s number
• Connect microscopic and macroscopic: PV = nMRT to

Force equation:

Solution: (assume a random force; yields a random walk)

Γ = 6πηa where η = viscosity = 1.02 × 10-3 Pa-s and a = radius of sphere

“Einstein, Perrin, and the reality of atoms: 1905 revisited”

Ronald Newburgh, Joseph Peidle, Wolfgang Rueckner

American Journal of Physics 74 6, June 2006

Equipment:

Celestron LCD Digital Microscope

(need 40x zoom, or about 0.25 μm/pixel)

Polysciences polystyrene microspheres 1 μm diameter (\$115—concentrated solution)

Saline solution for contact lenses (dilution)

Dimpled slides (Fisher Scientific, \$8.40/box of 12)

Coverslips

Coverslip placement

Calibration:

Borrow a calibrated slide from biology, or photograph a diffraction grating.

120 mm

Click on a sphere to follow it between successive images.

Positions are automatically collected in a table.

Calculate the squared displacement between photographs.

(or every other photograph, or every third, . . . )

Implementation summary:

Equipment:

Celestron LCD Digital Microscope

(need 40x zoom, or about 0.25 μm/pixel)

Polysciences polystyrene microspheres 1 μm diameter (\$115—concentrated solution)

Saline solution for contact lenses (dilution)

Dimpled slides (Fisher Scientific, \$8.40/box of 12)

Slide covers

ImageJ, available from NIH

“Einstein, Perrin, and the reality of atoms: 1905 revisited”

Ronald Newburgh, Joseph Peidle, Wolfgang Rueckner

American Journal of Physics 74 6, June 2006

Beth Parks, Colgate University, meparks@colgate.edu