4) In the photoelectric effect experiment, the graph of current versus battery v

Question

4) In the photoelectric effect experiment, the graph of current versus battery voltage for a metal with light of a particular frequency and intensity shining on it looks like the curve below. This graph represents current vs voltage for 200nm light shining onto Cadmium (Cd) which has a work function of4.07 eV. In the following questions you will be explaining why this curve has the shape that it does. a) Why is current level for V > 0? b) Why does current go to zero at some negative voltage and what determines that voltage? c) Why does current start decreasing steadily at V

Explanation / Answer

a) precisely for a voltage>0 the electrons will be "helped" by the electric field to reach the electrode, and there will be a current.

b) It goes to zero when the kinetic energy of the ejected electrons is not enough to "defeat" the electric field who's opposing their movement.

c) Because if the voltage is less than zero, the only thing which causes a current is the kinetic energy of the electrons.

d) i) Increasing the intensity does not change the graph.

ii) If you increase the frequency, the graph will be displaced to the left, because you will "defeat" with more kinetic energy sooner the electric field of the negative voltage.

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