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Photoelectric Effect Experiment: Intensity vs Current Curve

I did an experiment to test the effect of intensity on current using a photoelectric instrument that allows the control of light intensity, stopping voltage and frequency of light. The meter can read the current and stopping voltage.

The graph of the results I obtained showed that as intensity increased, the current increased linearly at first but the rate of change decreased past a certain intensity. Basically, the graph looks like a straight line that eventually starts to flatten out.

i'm not required to explain why this happens exactly, but I would like to know anyway. Can someone give a possible explanation for this? I think it's because after a certain intensity, some of the photons aren't hitting any electrons because they're all already illuminated.

Reply 1

piguy

The straight line part is standard (as you increase the intensity, the number of photons increase, so the number of electron's liberated per second increase, so the current increases proportionally). Though it's quite interesting that the line flattens out as you get to very high intensities. I'm thinking that if the intensity of the light is high enough (like Dr. Evil's laser), the metal plate will start to heat up quite a bit which will increase the resistance in the circuit. V=IR, so a higher resistance means the current would decrease if the voltage is staying the same.

(edited 10 years ago)

Reply 2

Rayexar

I haven't thought about the temperature increasing resistant because the light didn't seem to get really hot. it wasn't too bright either, much less bright than a regular light used in homes.

How much do you think the heat would affect the resistance? Does my guess in the first post sound reasonable, or is there something wrong with it?