Question

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

• A. 5400$A^0$
• B. 4000$A^0$
• C. 3100$A^0$
• D. 2200$A^0$

Answer 1

The correct option is C 3100$A^0$

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

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

$=\frac{1240}{4}(hc=1240ev-nm)$

$=310nm$
$=3100A.$
So, the answer is (C).