Follow by Email

Sunday, November 14, 2010

Graphs of photoelectric effect results



The formula quoted that intensity is proportional to frequency is correct but it is not reflected in the graph. It is also not the main feature of quantum physics to highlight this feature. Quantum is particulate so intensity is proportional to number of photons is the main story not frequency eventhough it is valid. Anyway the important graphs is featured to highlight the quantum aspect of light.
First graph: increasing the intensity increases the rate of photons but the freq remain the same hence photon energy is constant. Hence the photon releases the electron with the same KE thus indicating the same stopping potential . Increasing intensity here does not increase the freq( colour of the light is the same ) only brighter.
Second graph :The frequency is increasing so the intensity of the light increases but it is not related here. What is shown here is that the electron has greater KE as shown by stopping potential as the photon energy has increased. The emphasis here is not the overall intensity but the photon energy has increased.
Lets say for the first graph , you are told that intensity remain at I1 and the frequency increased , then you have to extend the stopping potential larger but the current is lower than before as the number of photons have reduced as a result of keeping intensity constant.