Question

The difference between threshold wavelengths for two metal surfaces \( A \) and \( B \) having work functions \( \phi_A = 9 \, \text{eV} \) and \( \phi_B = 4.5 \, \text{eV} \) is: \[ \text{(Given: } h c = 1242 \, \text{eV nm)} \]

• A. \( 264 \, \text{nm} \)
• B. \( 138 \, \text{nm} \)
• C. \( 276 \, \text{nm} \)
• D. \( 540 \, \text{nm} \)

Hint:

The threshold wavelength decreases as the work function increases. Use the formula \( \lambda = \frac{1242}{\phi} \) to find the relationship and ensure all units are consistent.