Midterm Question

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Siddiq 1E
Posts: 106
Joined: Fri Aug 09, 2019 12:15 am

Midterm Question

Postby Siddiq 1E » Mon Nov 25, 2019 11:17 am

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

Ariel Davydov 1C
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Joined: Thu Jul 11, 2019 12:16 am
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Re: Midterm Question

Postby Ariel Davydov 1C » Mon Nov 25, 2019 12:02 pm

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
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Joined: Sat Aug 17, 2019 12:18 am

Re: Midterm Question

Postby sarahforman_Dis2I » Mon Nov 25, 2019 12:38 pm

S 1C wrote: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
Posts: 106
Joined: Fri Aug 09, 2019 12:15 am

Re: Midterm Question

Postby Siddiq 1E » Tue Dec 03, 2019 9:50 pm

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
Posts: 90
Joined: Sat Sep 07, 2019 12:16 am

Re: Midterm Question

Postby ramiro_romero » Wed Dec 04, 2019 6:29 pm

S 1C wrote: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.


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