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Experiment to estimate the value of Planck's Constant using the Photo-Electric Effect

1. Preparation: a) Revise the basic ideas of quantum theory, especially Einstein's photo-electric equation.
b) See below.

In this method, light is allowed to reach a photo-emissive surface (inside a "photo-cell"). This causes electrons to be emitted with a range of kinetic energies. A "stopping voltage" is then used to stop even the most energetic of the emitted electrons before they reach the cathode of the photo-cell. A simplified diagram of the apparatus is shown below.

Find the voltage, Vs, needed to reduce the reading of the galvanometer to zero with a range of different frequencies of light, f, reaching the photo-cell (different coloured filters).
Einstein’s photo-electric equation can be stated as

eVs = hf – W

Use this to find a value of Planck’s constant, h.


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