Question

Work function of a metal is 2.1 eV. Which of the waves of the following wavelengths will be able to emit photoelectrons from its surface

• A. 4000 Å, 7500 Å
• B. 5500 Å, 6000 Å
• C. 4000 Å, 6000 Å
• D. None of these

Answer 1

The correct option is D None of these

Threshold wavelength ${\lambda }_0=\frac{12375}{2.1}=5892.8\AA$
So you need waves with wavelength lesser than threshold wavelength.