) A light source with intensity 1Wm2 shines on a piece of potassium. The binding

Question

) A light source with intensity 1Wm2 shines on a piece of potassium. The binding energy of the electrons in potassium is 1.8eV. The “Bohr radius” of an atom is 5.3×1011m is roughly the radius of a single atom. Assuming an atom perfectly absorbs all the radiation in it’s Bohr radius, how long will it take to collect enough energy to eject an electron? (6) b) In experiments, no matter how weak the radiation, if there is electron emission it always seems to start instantly. How is the calculation in part (a) wrong? (4)

Explanation / Answer

long will it take to collect enough energy to eject an electron = (1.8 * 1.6 * 10-19)/(1 * 4 * 3.14 * (5.3×1011)2)

                                                                                             = 8.163 sec

=>   the calculation in part (a) wrong due to weaker electron nucleus interaction .

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