1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Effect of resistance on photoelectric current

  1. Oct 2, 2013 #1
    1. The problem statement, all variables and given/known data
    Mmmm... Me and my classmate came across with this problem when studying photoelectric effect...

    Given a photocell connected to a circuit with a variable resistor (with resistance R) and an ideal ammeter. When a monochromatic light with frequency (f) (f>f0) and intensity (I) was shone on the photocell, would the photoelectric current (i) be affected by R? If yes, how could I find the photoelectric current?

    2. Relevant equations

    er... i=ne/t; E=nhf; etc. etc.

    3. The attempt at a solution

    At first we thought that the photoelectric current would be independent from R because the photoelectric current is proportional to number of photoelectrons reaching the anode end of the photocell and that in turn is only dependent on the number of photons shone on the cathode end of the photocell. But then if this is true then the photocell would be something like a 'constant-current' power source... As power input is limited by incident light intensity, if we just keep increasing R, wouldn't we reach a point where power output (i2R) would be larger than the power input (IA)?

    Then we considered the possibility of an effect on photoelectric current by R. But if yes, through what mechanism this is done? One attempt I made was that the increase in R would raise pd drop in the external circuit, which in turn would affect the number of photoelectrons reaching the anode end. But then this idea was a bit absurd in itself coz it involves a bit of a circular logic...

    I read a few related problems about photoelectric cell in this forum and thought this problem would have something to do with capacitance, which we have little knowledge on (as it is not covered by our syllabus)... Can someone shed some light on use? Many thanks~~
  2. jcsd
  3. Oct 7, 2013 #2
    If electrons accumulate at the cathode, the current in the photocell may not be equal to that through the resistor.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted