Photoelectric Effect
Quantum and Nuclear

A Nobel winner’s descent

Stories from Physics for 11-14 14-16 16-19 IOP RESOURCES

Philipp Lenard had been an assistant of Hertz and built on his work on the photoelectric effect. He discovered that the total charge of electrons emitted, but not their velocity, depended on the intensity of light shone on to the metallic surface. He went on to be awarded the Nobel Prize in 1905 for his work on cathode rays.

Lenard’s 1903 paper on the photoelectric effect was an important source for Einstein and the two physicists corresponded. Early in their communication, Einstein addressed Lenard as “Esteemed Professor!” and wrote “I thank you very much for the work you have sent me, which I have studied with the same feeling of admiration as your earlier works”. Lenard responded by addressing Einstein as his “highly esteemed colleague” and commented: “What could be more exciting for me than when a profound comprehensive thinker finds favour with some points from my work”. However, just a few years later, in a letter to a friend Einstein commented that Lenard’s ideas were “infantile” and bordered on the absurd.

In 1920, Einstein and Lenard had a public confrontation about general relativity at a meeting of the Association of German Scientists and Physicians. Lenard felt slighted by the awarding of the 1921 physics Nobel Prize for the photoelectric effect to Einstein alone, as he felt he had made a significant contribution to the research.

It is reported that Lenard had a tendency to jealousy and insecurity - he kept his laboratory locked out of fear of colleagues stealing his ideas and he required students to make obsequious comments about him in seminars.

He became caught up in the rising wave of German nationalism and anti-Semitism and was appointed ‘chief of Aryan science’ in the Nazi regime. He referred to relativity as “the Jewish fraud” and made other claims about the inferiority of “Jewish science”. When the US army occupied Heidelberg, the 83-year-old physicist attempted to flee but was captured. Though it was proposed that he be put on trial at Nuremberg, it was felt a greater punishment would be to ignore him and Lenard died two years later.


Photoelectric Effect
exhibits Quantisation
can be analysed using the quantity Photon Energy
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