Hallwachss electroscope

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Hallwachss electroscope

Hallwachss electroscope. This device was used in an 1888 experiment by the German physicist Wilhelm Hallwachs (1859-1922), the results of which were explained by J. J. Thomson. Light passing through the square hole in the black plate illuminates a round copper plate. Below this is an electroscope (cylinder) that is negatively charged (as seen by the thread attracted to one side). If the light is of sufficient energy, the electroscope will lose its charge (the thread falls). Thomson explained this as light causing electrons to be emitted from the copper plate, to be replaced by charge from the electroscope. Einstein, in 1905, used quantum theory to explain this photoelectric effect, and this won him the 1921 Nobel Prize for Physics

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Media ID 6410646

© VOLKER STEGER/SCIENCE PHOTO LIBRARY

Device Einstein Electric Charge Ether Experiment Experimenting Instrument Photoelectric Effect Quantum Physics Relativity Speed Of Light Electroscope Laboratory Physical Special Relativity

EDITORS COMMENTS
This print showcases Hallwachss electroscope, an instrumental device utilized in a groundbreaking experiment conducted by German physicist Wilhelm Hallwachs in 1888. The results of this experiment were later elucidated by the renowned J. J. Thomson. In the image, we observe light passing through a square aperture on a black plate, brilliantly illuminating a circular copper plate beneath it. Positioned below is an electrified cylinder-shaped electroscope, clearly indicated by the thread being attracted to one side. The crux of this experiment lies in understanding how light energy affects the electroscope's charge. If the light possesses sufficient energy, the electroscope will gradually lose its charge until finally discharging completely (indicated by the falling thread). J. J. Thomson attributed this phenomenon to electrons being emitted from the copper plate due to exposure to light and subsequently replaced with charge from the electroscope. Remarkably, it was Albert Einstein who further explained this intriguing photoelectric effect using quantum theory in 1905—an achievement that ultimately earned him the prestigious Nobel Prize for Physics in 1921. This photograph serves as a testament to both Hallwachs' pioneering research and Einstein's revolutionary contributions to physics. Displayed against a laboratory backdrop filled with scientific equipment and apparatuses, this image encapsulates key concepts such as electric charge, relativity theories like special relativity, quantum physics principles, and even references to ether—a concept once believed to be responsible for propagating light waves through space but later debunked by Einstein's work.

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