# What is the effect on charge of a metal when light frequency continues to increase above photoelectric work function?

For a given metal, light below a certain frequency will not eject an electron. Once the threshold or minimum energy is met to eject an electron, what happens as light frequency increases past the photoelectric work function? Do more and more electrons eject from the metal and thus the metal becomes increasingly positively charged? Or is there little difference in the number of electrons ejected (and hence charge of the metal) after the threshold frequency is met?

• Does this answer your question? What happens to a metal plate in the photoelectric effect? Jul 8, 2020 at 2:51
• I'm pretty clear on what happens to a metal plate in the photoelectric effect but less clear on what happens as light frequency continues to increase above the threshold frequency. Jul 8, 2020 at 2:57
• You are mixing the term intensity and frequency , be specific. Jul 8, 2020 at 2:59
• see this for frequency dependence hyperphysics.phy-astr.gsu.edu/hbase/mod2.html effects Jul 8, 2020 at 3:38

## 1 Answer

Do more and more electrons eject from the metal and thus the metal becomes increasingly positively charged?

Yes , more and more electrons will get ejected when you increase the frequency of the light.However, the rate of emission is still the same. Moreover in the experiment the metal is earthed to maintain electrical neutrality so that minimum energy required to eject an electron remains same i.e $$h \nu_0$$ remains same.

The only difference you will observe by increasing $$\nu$$ that electrons that are ejected (photo electrons) are ejected with higher kinetic energy.Number of photo electrons ejected per second remain same as intensity of light remains same.

The reverse happens when you change the intensity of light but $$\nu$$ of light is unchanged.

• "Yes , more and more electrons will get ejected " contradicts the later , and correct, "Number of photo electrons ejected per second remain same as intensity of light remains same." Jul 8, 2020 at 4:23
• @annav more and more electrons had nothing to do with photo emissions per second , It meant that total number of electrons ejected will increase . Jul 8, 2020 at 4:48
• Note the title "when light frequency continues to increase above photoelectric work function", frequency , not intensity. Jul 8, 2020 at 5:20
• @annav more and more electrons as in over a period of time (I meant the number of electrons ) will get ejected with same kinetic energy, In simple term if in one second 1 electron was ejected then i one minute 60 electrons will get ejected with i.e 59 more electrons. Jul 8, 2020 at 5:29