### JEE Mains Previous Years Questions with Solutions

4.5
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### AIEEE 2002

Sodium and copper have work functions $2.3$ $eV$ and $4.5$ $eV$ respectively. Then the ratio of the wavelengths is nearest to
A
$1:2$
B
$4:1$
C
$2:1$
D
$1:4$

## Explanation

We know that work function is the energy required and energy $E = h\upsilon$

$\therefore$ ${{{E_{NA}}} \over {{E_{Cu}}}} = {{h{\upsilon _{Na}}} \over {h{\upsilon _{cu}}}} = {{{\lambda _{cu}}} \over {{\lambda _{Na}}}}$

$\left[ {\,\,} \right.$ as ${\,\,\,\upsilon \propto {1 \over \lambda }}$ for light $\left. {\,\,} \right]$

$\therefore$ ${{{\lambda _{Na}}} \over {{\lambda _{Cu}}}} = {{{E_{Cu}}} \over {{E_{Na}}}} = {{4.5} \over {2.3}} \approx {2 \over 1}$