Question
The difference between threshold wavelengths for two metal surfaces $A$ and $B$ having work function $\phi_A=9\,eV$ and $\phi_{ B }=4.5\,eV$ in $nm$ is:(Given, $hc =1242\,eV\,nm$)
✓
Answer
$\lambda_{ A }=\left(\frac{1242}{9}\right)=138\,nm$
$\lambda_{ B }=\left(\frac{1242}{4.5}\right)=276\,nm$
$\lambda_{ B }-\lambda_{ A }=138\,nm$
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