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Jimbo
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Hello,
I am trying to understand an equation stated in the book 'Principles of Protein X-Ray Crystallography' by Jan Drenth (The exact page I am reffering to can be found here: http://books.google.co.uk/books?id=...y crystallography&pg=PA24#v=onepage&q&f=true")
The page discusses electrons being accelerated between a cathode and an anode, and the x-rays emitted as part of the process. It mentions a cut off wavelength where "photons obtain their full energy from the electrons when they reach the anode", and states that electron energy = electron charge * accelerating voltage and that photon energy is planks constant * (speed of light / wavelength) and that the minimum wavelength is therefore 12.4 / V where V is in kilovolts.
My working is as follows:
When the photons obtain their full energy from the electrons, eV = hc / λ
So, λ = hc / eV (as stated in the book)
hc = 1.24 * 10-6 eVm
So just looking at the units I get:
eVm / eV which makes sense as I am left with m for the wavelength.
But my question is where does the V come from in the books equation? (They state that λ = 12.4 / V)
Also why is this necessarily the minimum wavelength? (it is stated as λmin) Why not just wavelength?
Sorry for the long introduction but I wanted to give my question a bit of context.
Thanks very much for any guidance,
Jimbo
I am trying to understand an equation stated in the book 'Principles of Protein X-Ray Crystallography' by Jan Drenth (The exact page I am reffering to can be found here: http://books.google.co.uk/books?id=...y crystallography&pg=PA24#v=onepage&q&f=true")
The page discusses electrons being accelerated between a cathode and an anode, and the x-rays emitted as part of the process. It mentions a cut off wavelength where "photons obtain their full energy from the electrons when they reach the anode", and states that electron energy = electron charge * accelerating voltage and that photon energy is planks constant * (speed of light / wavelength) and that the minimum wavelength is therefore 12.4 / V where V is in kilovolts.
My working is as follows:
When the photons obtain their full energy from the electrons, eV = hc / λ
So, λ = hc / eV (as stated in the book)
hc = 1.24 * 10-6 eVm
So just looking at the units I get:
eVm / eV which makes sense as I am left with m for the wavelength.
But my question is where does the V come from in the books equation? (They state that λ = 12.4 / V)
Also why is this necessarily the minimum wavelength? (it is stated as λmin) Why not just wavelength?
Sorry for the long introduction but I wanted to give my question a bit of context.
Thanks very much for any guidance,
Jimbo
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