# Illustration A straight line in the energy-frequency diagram results in the photoelectric effect

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An energy-frequency graph that arises from the photoelectric effect. The maximum kinetic energy $$W_{\text{kin}}$$ of an electron is plotted on the vertical axis and the frequency $$f$$ of the light is plotted on the horizontal axis. The photons of the light are used to eject the electrons for example from a metal plate.

In the photoelectric effect, the kinetic energy depends linearly on the light frequency. This results in a straight line in the graph. From the straight line, we can determine the cutoff frequency $$f_0$$ (x-axis intercept) and the work function $$W$$ (y-axis intercept). These quantities tell us which material is irradiated with light.

From the slope of the straight line the physical constant $$h$$ (Planck's constant) can be calculated.