Question

The work function of a substance is 3.0 eV. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately:

• A. 215 nm
• B. 400 nm
• C. 414 nm
• D. 200 nm

Answer 1

Answer: (C)

414 nm

Answer 2

For photoelectric emission, the energy of the photon must be equal to or greater than the work function $W_e$:

$\lambda = \frac{hc}{W_e}$

Using $h = 1240 \, \text{nm} \times \text{eV}$ and $W_e = 3.0 \, \text{eV}$:

$\lambda \leq \frac{1240 \, \text{nm} \times \text{eV}}{3.0 \, \text{eV}} = 413.33 \, \text{nm}$

Thus, $\lambda_{\text{max}} \approx 414 \, \text{nm}$.