Question

The work function of a substance is 4 eV. What is the approximate longest wavelength of light that can cause photo-emission?

• A. 309 nm
• B. 209 nm
• C. 109 nm
• D. 9 nm

Answer 1

Answer: (A)

309 nm

Answer 2

λ_th = $\frac { \mathrm { hc } } { \phi }$= $\frac { 12400 } { 4 } \AA$= 3100 Å = 310 nm

λ ≤ λ_th

⇒ λ ≤  310 nm