Question
The work function for tungsten and sodium are $4.5 eV$ and $2.3 eV$ respectively. If the threshold wavelength $\lambda $ for sodium is $5460{Å}$, the value of $\lambda $ for tungsten is ............ $\mathop {\rm{A}}\limits^o $
✓
Answer
(c) Since ${W_0} = \frac{{hc}}{{{\lambda _0}}}$;
$\therefore \;\frac{{{{({W_0})}_T}}}{{{{({W_0})}_{Na}}}} = \frac{{{\lambda _{Na}}}}{{{\lambda _T}}}$ or ${\lambda _T} = \frac{{{\lambda _{Na}} \times {{({W_0})}_{Na}}}}{{{{({W_0})}_T}}}$$ = \frac{{5460 \times 2.3}}{{4.5}} = 2791\;{Å}$
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