Question

what change would you make to a sodium system to increase the kinetic energy of the ejected electrons, but not change the number of electrons ejected?
$w_{na} = 3.68 \times 10^{-19}$ j
increase the frequency of the light.
increase both the intensity and wavelength of the light.
increase the wavelength of the light.
increase the intensity of the light.

Explanation:

The kinetic energy of ejected electrons in the photoelectric effect follows the equation $KE = h
u - W$, where $h
u$ is the photon energy, and $W$ is the work function of sodium. Increasing light frequency ($
u$) raises photon energy, increasing electron kinetic energy. The number of ejected electrons depends on light intensity (number of photons), so keeping intensity constant ensures the number of electrons does not change. Increasing wavelength decreases frequency, reducing kinetic energy. Increasing intensity only changes the number of electrons, not their kinetic energy. Changing both intensity and wavelength alters both electron count and kinetic energy.

Answer:

Increase the frequency of the light.