Question

The work function of a substance is $4eV$. The longest wavelength of light that can cause photoelectron emission from this substance is approximately.

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

Answer 1

The correct option is B 310 nm

Photoelectric emission will happen from the material as long as the incident light's energy is greater than the work function.
$\frac{hc}{\lambda }>4.0eV$
$\Rightarrow \lambda <\frac{hc}{4eV}$

$\Rightarrow \lambda <\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{4\times 1.6\times {10}^{19}}$

$\Rightarrow \lambda <310nm$