Question

An isolated metal body is illuminated with monochromatic light and is observed to becomes charged to a steady positive potential 1.0 V with respects to the surrounding. the work function of the metal is 3.0 eV. The frequency of the incident light is______

Answer 1

By Einstein's Photoelectric equation

$eV=h\nu -\varphi$

where $V=1V=$ cutoff voltage

$⟹\nu =\frac{eV+\varphi }{h}=\frac{4eV}{h}=\frac{4\times 1.6\times {10}^{-19}}{6.63\times {10}^{-34}}$

$⟹\nu =9.6\times {10}^{14}Hz$