FRANK HERTZ EXPERIMENT IONIZATION POTENTIAL Apparatus When V increases I increases When V is about Ionization Potential 13 6V for Hydrogen electrons have enough energy to free other electrons from hydrogen With more electrons More electrons to contribute to current Current increases sharply with voltage To obtain ionization energy for an atom put in apparatus and measure I vs V Where I increases more rapidly give Ionization Voltage and thus Ionization Energy FRANCK HERTZ EXPERIMENT Apparatus See Figure 4 20 in Thornton and Rex The collector is negative relative to Grid The electrons gain energy as they approach grid More and more have enough energy to overcome retarding potential so current increases But as voltage on grid increases electrons gain energy When electron has energy equal to energy difference between the ground state and first excited state it looses that energy These electrons can no longer overcome the retarding potential and the current drops See Figure 4 2 in Thornton and Rex Page 15
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