Teaching Physics with the Physics Suite
Edward F. Redish
Modern theories of atoms describe them not just as little particles but also say they should have wave properties. If this is so, then passing a beam of atoms through a double slit should produce an interference pattern. The figure at the right, taken from an article in Physical Review Letters,* shows the result of passing a beam of Helium atoms through a double slit.
The slits are 8 μm apart and the screen collecting the atoms is 64 cm away from the slits. If the peaks that are seen in the figure are two-slit interference peaks, what would be the wavelength of the atoms? Explain your reasoning. (Note: This was the first experiment demonstrating interference with whole atoms. The data is a bit ragged since it was difficult to get a sharp wavelength – which is determined by the velocity of the atoms in the beam. The agreement of this measured value with the predicted theoretical wavelength was a convincing argument that the experimenters had actually seen the phenomenon.)
* O. Carnal and J. Mlynek, “Young’s double slit experiment with atoms,” Phys. Rev. Lett. 66 2689 (1991)
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