Midterm Question

[Siddiq 1E]

Hi, I still don't understand why the correct answer for the graph on the midterm isn't just linear.

[Ariel Davydov 1C]

Hi! So on this graph, we were supposed to illustrate the number of electrons emitted once the photons reached a certain frequency. In order to approach this problem, you must remember that all the equations we are given (E=hv, E - work function = KE) is calculating the energy of ONE PHOTON or ONE ELECTRON, since the photoelectric effect occurs on a one-to-one basis. The question stated that all throughout this experiment, the photons projected were held at a constant intensity, meaning the number of photons stayed constant all throughout. Thus, the number of electrons (once ejected) must stay constant as well, meaning the graph would just be a straight line across, regardless of the frequency. Hope this helps!

[sarahforman_Dis2I]

Hi, I still don't understand why the correct answer for the graph on the midterm isn't just linear.

The reason that the graph is a horizontal is that the question states that the intensity of the light is kept constant. This is extremely important because a constant intensity means that there are the same number of photons being released. Increasing the frequency just means that each photon will have a higher amount of energy, not that there will be more photons ejected. This means that since the intensity is constant, once the frequency of each photon reaches the threshold energy of the metal, the amount of electrons emitted will not depend on the energy of the incoming light. As long as the frequency is above the threshold energy and the intensity is constant, the amount of electrons ejected will not change. What will change is the ke of the electrons themselves.

[Siddiq 1E]

Thank you all for the replies -- I get why it goes across now, but I still don't understand why it goes straight up?

[ramiro_romero]

Thank you all for the replies -- I get why it goes across now, but I still don't understand why it goes straight up?

When the threshold frequency is met, the electrons are emitted instantly. If it were to be linear it would assume that electrons are emitted as frequency increases which is not the case.