Question

The work function of a substance is $4.0eV$. The longest wavelength of light that can cause photo-electric emission from this substance is approximately

• A. $220nm$
• B. $310nm$
• C. $540nm$
• D. $400nm$

Answer 1

The correct option is B $310nm$

$\varphi =\frac{hc}{{\lambda }_M}$

$4eV=\frac{1240}{{\lambda }_M}(hc=1240eV-nm)$

${\lambda }_M=\frac{1240}{4}$
$=310nm$
So, the answer is option (B).