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

Answer 1

Answer: (C)

The minimum energy of incident radiations, required to eject the electrons from metallic surface is defined as work function of that surface.
$W_0=h{v}_0=\frac{hc}{{\lambda }_0}$
where ${\lambda }_0=$ threshold wavelength.
Work function in electron volt $W_0(eV)$
$W_0=\frac{12400}{{\lambda }_0(\mathring{A})}eV$
$\therefore 4.0=\frac{12400}{{\lambda }_0}$
$\Rightarrow {\lambda }_0=310nm$