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March 28, 2017

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Under the correct conditions, the element molybdenum emits X-rays with a characteristic wavelength of 0.711A (7.11*10^-11m). These X-rays are used in diffraction experiments to determine molecular structures. How fast does an electron need to be moving to have the same wavelength as these X-rays?

Wavelength=h/mv

7.11*10^-11m= (6.626*10^-34J*s) / mv

I'm stuck. How do I know what "m" is? Is it just the atomic mass of Molybdenum, 95.9amu?

  • Chemistry - ,

    No. Aren't you interested in the speed of the electron. So it's the mass of the electron (in kg I think).

  • Chemistry - ,

    Oh, yes that's right. Mass of electron= 9.11*10^-31kg.

    Therefore v=1.02*10^7m/s

  • Chemistry - ,

    That looks ok to me. I didn't check the arithmetic.

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