Photoelectric Effect Post-Assessment Module #18

[juleschang16]

Which is the correct answer and can you explain why?

In the photoelectric effect what condition must occur for an electron to be emitted from a metal surface?

A. E (photon) > 0

B. E (photon) < E (remove e-)

C. E (photon) = E (remove e-)

D. E (photon) > E (remove e-)

E. C and D

[Cody Do 2F]

Hi Jules!

The correct answer is E: both C and D are correct!

During Dr. Lavelle's lecture for the Photoelectric Effect, one of the key concepts he highlighted was that unless Energy of a Photon is greater than or equal to the Energy used to remove an electron, then no electron is emitted. In essence, he's saying that an electron requires x amount of energy to be removed. If a photon has exactly x energy or more than x energy, then the electron will be emitted. If the photon has less than x energy, then no photon is emitted.

Hope that helps!

[Hai-Lin Yeh 1J]

The answer is E) both C and D because the work function (also called your threshold energy) indicates how much energy is needed to eject an electron. (Think of it like a threshold, you need to reach a certain level for something to occur). Therefore, if you have more than enough, that is E(photon) > E (remove e-), then electrons will definitely be ejected. You will just end up with excess kinetic energy. If you have just the right amount [that is E (photon) = E (remove e-)], your kinetic energy will be 0, but there still is enough because you have reached the threshold. Only when E(photon) < E (remove e-) [in this case, the energy of the photon is not enough] will an electron NOT be emitted from the metal surface.

Essentially, think of it like this: there are 2 conditions in which an electron is ejected from the metal surface:
E(photon) > E (remove e-) OR E (photon) = E (remove e-). The energy of the photon can never be less than your work function (threshold energy).