Question

The work function of potassium metal is 2.30 eV. Monochromatic light is shined on its surface, and photoelectrons with a maximum speed of 7.50E5 m/s are ejected. What is the wavelength of the light?

Group of answer choices

539 nm

657 nm

393 nm

319 nm

1443 nm

Answer 1

K.E (max) = (hc / $\lambda$ ) - $\phi$

where

K.E (max) = 1/2 * 9.1e-31 * 7.5e5² = 2.56e-19 J or 1.598 eV

so,

1.598 eV = (1240 eV . nm / $\lambda$ ) - 2.30

$\lambda$ = 319 nm