Question

The work function of a substance is 4.0 eV. 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)

310 nm

Minimum energy required for photoelectron emission is the work potential= $4eV$

Energy of photon=$\frac{hc}{\lambda }$

$⟹\frac{hc}{{\lambda }_{max}}=4eV$

${\lambda }_{max}=\frac{(6.626\times {10}^{-34})\times (3\times {10}^8)}{4\times 1.6\times {10}^{-19}}\approx 310nm$