Photoelectric Effect Homework: Current & Frequency

[wany]

Homework Statement

This has to do with a simple photoelectric effect setup:
If there is no current, would increasing the frequency of the light result in at least some current?
If there is some current, would increasing the frequency result in a maximum current?

Homework Equations

The Attempt at a Solution

So I was thinking that I know that changing the frequency results in a change of the stopping voltage. A higher frequency means a greater stopping voltage and a smaller frequency means a smaller stopping voltage. So if there is no current, wouldn't increasing the frequency give at least some current from this reasoning.

Secondly, if there is some current, then increasing the frequency will not result in a maximum current.

Is this correct?

 

[vela]

Homework Statement

This has to do with a simple photoelectric effect setup:
If there is no current, would increasing the frequency of the light result in at least some current?
If there is some current, would increasing the frequency result in a maximum current?

Homework Equations

The Attempt at a Solution

So I was thinking that I know that changing the frequency results in a change of the stopping voltage. A higher frequency means a greater stopping voltage and a smaller frequency means a smaller stopping voltage. So if there is no current, wouldn't increasing the frequency give at least some current from this reasoning.

I don't see how it follows that a change in stopping voltage corresponds to current. Also, the question is a bit vague.

Secondly, if there is some current, then increasing the frequency will not result in a maximum current.

Is this correct?

Why or why not? It sounds like you're just guessing here. Under what conditions do you get the maximum current?

 

[wany]

well I based this off of a graph such as the one in this link (the first graph)
http://www.cobalt.chem.ucalgary.ca/ziegler/educmat/chm386/rudiment/tourexp/photelec.htm

So let us say there is no current. But if you increase the frequency, wouldn't that mean you can get some current to show since you would "jump" onto a higher curve?

And for the second part, I am not sure but again using the graph you would not get a max.

 

[vela]

well I based this off of a graph such as the one in this link (the first graph)
http://www.cobalt.chem.ucalgary.ca/ziegler/educmat/chm386/rudiment/tourexp/photelec.htm

So let us say there is no current. But if you increase the frequency, wouldn't that mean you can get some current to show since you would "jump" onto a higher curve?

Not necessarily. Can you explain how the photoelectric effect works?

And for the second part, I am not sure but again using the graph you would not get a max.

 

[wany]

Yes. So basically, a light source hits a metal, and if the energy of each photon is higher than the work function then electrons will be emitted from the metal. Then you have a battery attached to the two wires in order for a positive charge to be built up on the other side so the electrons are attracted to it thus "finishing" the loop in order to produce a current.

 

[vela]

Good. So if there's no current, why would that be? How would increasing the frequency of the light affect this?

 

[wany]

I see your point were frequency does not have anything to do with current, I mean I understand that, frequency just has to do with the amount of energy each photon has, whereas current has to do with the intensity of the light source.

But what if say the work function of the metal is like 4 eV, and each photon right now has 3eV. So obviously electrons won't be emitted. Now you raise the frequency of the light so each photon has say 5eV. So now electrons are emitted. So now wouldn't there be a current?

 

[vela]

Yes, and your question gets to why I said the original question was vague. Suppose you increased the energy to 3.5 eV. It's still below the work function, so you'd still get no current. On the other hand, suppose you're already at 5 eV and increase to 6 eV. This increases the kinetic energy with which the electrons are ejected. Do you get more current? Under some conditions you will; under others you won't.

 

[wany]

Ya, that is what I was thinking. Ill ask the teacher about it, because this question could be answered in several ways.

Thank you for your help.