Question

A photoelectric emission apparatus with an unknown metal is irradiated with 200 nm light. The photocurrent becomes zero at the collector plate potential of –0.80 V. 

Determine the work function of the unknown metal. 

Take h = 4.13 × 10^-15 eV-s. 

Answer 1

Maximum KE of the emitted photoelectrons: 

KE_max = e ΔV = e x 0.8 = 0.8 eV

Work function = hν - KE_max 

= (h c/λ) - KE_max

_{\( = \frac{(4.13\times10^{-15}\times3\times10^8)}{\lambda} - KE_{max}\)} 

_{\(= \frac{(12.40\times10^{-7}\ eV - m} {\lambda} - 0.8\ eV\)}  

_{\(\frac{1240\ eV - nm}{200\ nm} - 0.8\ eV = 5.4\ eV\)}