Question
Threshold wavelength for photoelectric effect on sodium is $5000\;\mathring A$. Its work function is
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Answer
(c) ${W_0} = \frac{{hc}}{{{\lambda _0}}} = \frac{{6.625 \times {{10}^{ - 34}} \times 3 \times {{10}^8}}}{{5000 \times {{10}^{ - 10}}}}J = 4 \times {10^{ - 19}}J$
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