How does the Franck-Hertz experiment demonstrate energy quantization in atoms?

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The Franck-Hertz experiment demonstrates energy quantization in atoms by showing that electrons can only lose specific amounts of kinetic energy, specifically 4.9 electron volts, when colliding with mercury atoms. This energy loss corresponds to the excitation potential energy of the atom, leading to periodic minima in the anode current. The observed periodicity is linked to resonance, where the kinetic energy of electrons near multiples of 4.9 eV results in increased absorption and energy loss. This experiment provides clear evidence of quantized energy levels within atoms.

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In the experiment, it is observed that the minimum value of anode current occurs periodically and its period multiplied with e is known as excitation potential energy.

I don't see the link between this periodicity and quantisation of energy levels of atom.
Could anyone please make this clear?
 

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Pushoam said:
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In the experiment, it is observed that the minimum value of anode current occurs periodically and its period multiplied with e is known as excitation potential energy.

I don't see the link between this periodicity and quantisation of energy levels of atom.
Could anyone please make this clear?
From the wiki article.
It seems the periodicity is a resonance.When the KE is near a multiple of the 4.9eV energy then absorption is more likely.

They discovered that, when an electron collided with a mercury atom, it could lose only a specific quantity (4.9 electron volts) of its kinetic energy before flying away.[4] This energy loss corresponds to decelerating the electron from a speed of about 1.3 million meters per second to zero.[5] A faster electron does not decelerate completely after a collision, but loses precisely the same amount of its kinetic energy. Slower electrons merely bounce off mercury atoms without losing any significant speed or kinetic energy.
 

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