Question

The work function of a sunstance is 4eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately.
[AIEEE-2004]

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

Answer 1

The correct option is C 310 nm

Photoelectric emission will happen from the material as long as the incident light's energy is greater than the work function.
$\frac{hc}{\lambda }>4.0eV$
$\Rightarrow \lambda <\frac{hc}{4eV}$
$\Rightarrow \lambda <\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{4\times 1.6\times {10}^{19}}$
$\Rightarrow \lambda <310nm$