Work function

[Sophia Henry]

In order to study for the 14A final exam I am going back through my old notes and I came across confusion surrounding this concept: The photoelectric effect is a concept put forth by Planck and it basically describes how photons are ejected from metals when electron excitement takes place. The plancks equation says that E=hv or energy of individual photon is the planck constant times the frequency of the photon. Something I came across though is the equation for the kinetic energy of an ejected electron which is 1/2(m of e-)(v^2)=hv-work function. This equation made me feel very confused because it made me feel less confident about Planck's photelectric effect equation. But these concepts are written down right next to each other in my notes so I am wondering how they are related. Because I know that the work function is the energy needed to remove the electron and then that relates to the photoelectric effect because a removed electron is how a photon gets released. But here's my question: is that even right? I'm worried I'm correlating unrelated things and confusing two separate concepts. Can someone explain how those two equations interact or correlate? Are they the same thing and are they describing the same thing in just different ways? If yes, why are they different. I don't understand why we have these two equations because the second equation seems like a redundant more complicated version of the first equation..

[306060519]

They are incredibly related and target the same principals, but you need to look at them as if you would look at the same piece of art from two different perspectives. They are related to each other, but cover different variable aspects of the same situation. Good luck studying.

[Levy Shaked]

By first looking at this qualitatively in terms of energy transfer, we can say that the KINETIC energy of an emitted electron is equal to the ELECTROMAGNETIC energy of the photon that frees it, minus the work done on the electron by its parent atom in binding it. In other words, light energy is converted to energy of motion if the light energy is capable of overwhelming the work function, or the energy with which the atom's nucleus binds its electron.

By this relationship, K(electron) = E(light) - W(atom); that is, an electron's kinetic energy is equal to the difference between the energy of the photon that freed it and the energy with which it was bound.

The kinetic energy of a particle is equal to 0.5mV^2, and the energy of light is equal to hv (the v in this equation represents the FREQUENCY of the light wave, not to be confused with the VELOCITY that is a component of the kinetic energy equation). Thus, the relationship above is equivalent to:

0.5mV(electron)^2 = hv(light) - W(atom)