Download Gustav Robert Kirchhoff

Gustav Robert Kirchhoff
A Brief Digest of His
Life and Work
by Mike Rasmussen
Vital Statistics
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Born: 12 March 1824, Königsberg, Prussia
Christened: 11 April 1824
Father: Friedrich Kirchhoff (lawyer)
Mother: Johanna Henriette Wittke
Married: 1847, to Clara Richelot (his math professor’s daughter
– good reason to study math!)
Died: 17 October 1887, Berlin
Temple work: Done several times, 1929-2001. (Often just
sealed to Mr. and Mrs. Kirchhoff – good reason to study
physics!)
Scientific contributions in brief
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Kirchhoff’s Law (Thermodynamics)
Kirchhoff’s Circuit Laws
Spectroscopy (with Bunsen)
Fresnel-Kirchhoff diffraction formula.
Kirchhoff’s Law (Thermodynamics)
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At thermal equilibrium, light emitted equals
light absorbed.
(Otherwise it wouldn’t be at equilibrium.)
So, black bodies are great emitters.
And “Space Blankets” are good at not
emitting.
Kirchhoff’s Circuit Laws
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The Sum of voltage rises and drops around a loop
equals zero.
(Energy is conserved.)
Currents entering a junction are equal to currents
leaving a junction.
(Charge is conserved, similar to thermodynamic law.
Remember, a lot of people thought charge was like
heat, and might accumulate at a junction.)
So, we can do circuit analysis.
Obvious, but useful – maybe we can all get laws
named after us someday!
Kirchhoff and Bunsen
Spectroscopy
“Two old telescopes, a prism, and a cigar box”
A Great Spectroscopy Experiment
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Burned highly purified sodium, observed two
strong yellow lines
Lit a Drummond light, which is a stick of lime
heated by a flame to white hot – it radiates
nearly as a black body, with no dark lines
Lit a sodium flame in between the “limelight”
and the spectroscope, and observed two
dark lines – the sodium absorbed more
energy than it emitted
Spectroscopy results
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Identified Fraunhofer’s yellow lines in several
lamp spectra as sodium emission
Identified Fraunhofer’s dark lines in the solar
spectrum as absorption
Identified the chemical content of the sun
Identified Cesium and Rubidium
Fresnel-Kirchhoff diffraction formula.
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Fresnel derived a formula for diffraction by
applying Newton’s calculus to Huygen’s
wavelets.
In 1887, Kirchhoff used Maxwell’s Equations
to justify Fresnel’s formula.
Hence, it was named after both Fresnel and
Kirchhoff.
Apparently, it killed him, as he died that year.
References
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http://en.wikipedia.org/wiki/Gustav_Kirchhoff
www.familysearch.org
http://dbhs.wvusd.k12.ca.us/webdocs/ChemHistory/Kirchhoff-Bunsen-1860.html
http://www.neatherd.org/astronomy/Fingerpri
nts%20of%20light.htm
http://optics.byu.edu/Textbook.htm