# Lorentz, Hendrik Anton

### electrons physics theory theoretical

[loh rents] (1853–1928) Dutch theoretical physicist: contributed greatly to the theory of the electron and of electromagnetism.

Lorentz completed his studies early at Arnhem and Leiden; a thesis on light reflection and refraction won him the first chair of theoretical physics in Holland at Leiden when he was 24. In 1912 he became director of the Teyler Institute, Haarlem. He did a great deal to found theoretical physics as an academic discipline in Europe.

Lorentz’s thesis showed how to solve equation when an interface between two materials is present. He was then able to predict the formula for the behaviour of light in a moving medium. In 1892 his ‘electron theory’ was published; it regarded electrons as embedded in the ether, which transmitted Maxwell’s electromagnetic fields and obeyed an additional relation for the force of the field on the electron (1895), now known as the Lorentz force. The Lorentz force was proposed independently by (1889). Lorentz showed, by averaging microscopic forces on electrons to give macroscopic forces on materials, how Maxwell’s ‘displacement current’ arises and why an additional term is needed. These results were later confirmed by experiment. Lorentz adopted the word ‘electron’ in 1899, and identified electrons with cathode rays. He showed how vibrating electrons give rise to Maxwell’s electromagnetic waves, and with explained the Zeeman effect whereby atomic spectral lines are split in the presence of magnetic fields (1896). For this work Lorentz and Zeeman were awarded the 1902 Nobel Prize for physics. So successful was the ‘electron theory’ that its failure to explain the photoelectric effect was a major clue to the need for quantum theory.

Lorentz studied the result of the experiment, which gave no indication that the Earth was moving through the hypothetical ether. He showed that if moving bodies contracted very slightly in the direction of motion, the observed results could occur. Derived independently by , this is known as the Lorentz–FitzGerald contraction. In 1904 Lorentz developed a firm mathematical description of this, the Lorentz transformation, and this was later shown by Einstein to emerge naturally out of his special relativity theory (1905).

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