Question

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

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

Answer 1

The correct option is B 310 nm

Work function of metallic substance $\varphi =4.0eV$
For photoelectric effect to take place, minimum energy of the incident photon must be equal to the work function of metal surface i.e. $E_{min}=\varphi$
$\therefore$ $\frac{hc}{{\lambda }_{max}}=\varphi$
Or ${\lambda }_{max}=\frac{hc}{\varphi }$
Or ${\lambda }_{max}=\frac{1240}{\varphi \left(ineV\right)}nm$
$⟹{\lambda }_{max}=\frac{1240}{4}=310nm$