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: Photoelectric effect

  1. Mar 15, 2010 #1
    Hi there,

    Im having a problem with the results im getting for an experiment Im doing in relation to the photoelectric effect. My graph is very similar to that in the attachment, except for the fact that the line at A and again after the drop is sloping at a very steep angle to begin with.

    To me this means that the current is varying with the portential before the saturation voltage is reached...does this make any sense? Should i be grounding something other then the obvious maby?

    My setup is a zinc cathode within a copper tube under vacume. Im directing uv light from a mercury vaper lamp through a quartz window at the cathode.

    Any thoughts would be some help, im getting the correct work functions but im curious to know why its different?


    Attached Files:

  2. jcsd
  3. Mar 16, 2010 #2
    As with many experimental issues, such a short description of methods and procedures will not be very useful to determine the exact cause. For instance, what is a copper tube exactly, and how is it oriented relative the zinc cathode, and what is the geometry of the cathode and anode, what is their spacing, etc. It will be very difficult to say without some real information!

    Nevertheless, if it is linear it is consistent with ohmic behavior. If there is a leak in the vacuum tube or the gas is ionized, or if there is a buildup of material on the cathode/anode gap etc to provide a conductive path in addition to the photocurrent then you may see a sum of the two currents which would give something like the result you are getting. However, this may not be consistent with the voltages you are applying, again information would help. Good luck!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook