The first three energy levels of the fictitious element X were shown in FIGURE P38.56. An electron with a speed of 1.4 × 10⁶m/s collides with an atom of element X. Shortly afterward, the atom emits a photon with a wavelength of 1240 nm. What was the electron??s speed after the collision? Assume that, because the atom is much more massive than the electron, the recoil of the atom is negligible.

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E (eV) 0.00 n= 3 – --2.00 n= 2 -3.00 FIGURE P38.56 n=1- -6.50