Q.The stopping potential for photoelectrons emitted from a metal surface under a certain illumination is measured to be $1.5\ \text{V}$. Calculate the maximum kinetic energy of the emitted photoelectrons, in both electron-volts and joules.

Saturation current counts the total number of photoelectrons emitted per second, which is set by how many photons strike the metal per second — i.e. the intensity of light, not its frequency.

In the photoelectric effect, when the collector plate is made sufficiently positive, ALL photoelectrons ejected from the metal surface are collected, and the photocurrent reaches a maximum, constant value called the saturation current — increasing the collector voltage further does not increase it any more.

…

Einstein's photoelectric equation rearranged in terms of stopping potential is linear in frequency with slope h/e.

Einstein's photoelectric equation is $h\nu = \phi_0 + eV_0$, where $V_0$ is the stopping potential and $\phi_0$ the work function. Rearranging for $V_0$:

$V_0 = \dfrac{h}{e}\nu - \dfrac{\phi_0}{e}$

…

The stopping potential is the potential that just stops the fastest photoelectrons, found by equating eV0 to their maximum kinetic energy.

The stopping potential V0 is defined by the condition that the retarding field decelerates even the most energetic photoelectrons (of maximum speed v) to rest just before they reach …