Question

The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photo electron emission from this substance is approximately :

• A. 540 nm
• B. 440 nm
• C. 310 nm
• D. 220 nm

Answer 1

The correct option is C 310 nm

$W_0=h{v}_0=\frac{hc}{{\lambda }_0}$

Work function in electron volt is $4eV$

$W_0=\frac{12400}{{\lambda }_0}=eV$

$40=\frac{12400}{{\lambda }_0}$ ${\lambda }_0=310nm$