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The classical setup to observe the photoelectric effect includes a light source, a set of filters to monochromatize the light, a vacuum tube transparent to ultraviolet light, an emitting electrode (E) exposed to the light, and a collector (C) whose voltage V C can be externally controlled. [citation needed]
Because light can travel through a vacuum, it was assumed that even a vacuum must be filled with aether. Because the speed of light is so great, and because material bodies pass through the aether without obvious friction or drag, it was assumed to have a highly unusual combination of properties. Designing experiments to investigate these ...
In explaining the photoelectric effect, the hypothesis that energy consists of discrete packets, as Einstein illustrates, can be directly applied to black bodies, as well. The idea of light quanta contradicts the wave theory of light that follows naturally from James Clerk Maxwell 's equations for electromagnetic behavior and, more generally ...
[64]: 231–236 In 1905, Albert Einstein published the theory of the photoelectric effect. It appeared that the only possible explanation for the effect was the quantization of light itself. Later, Niels Bohr showed that atoms could only emit discrete amounts of energy.
The source of Einstein's proposal that light was composed of particles (or could act as particles in some circumstances) was an experimental anomaly not explained by the wave theory: the photoelectric effect, in which light striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage.
Photomagnetism (photomagnetic effect) is the effect in which a material acquires (and in some cases loses) its ferromagnetic properties in response to light. The current model for this phenomenon is a light-induced electron transfer , accompanied by the reversal of the spin direction of an electron .
The notions of light as a particle resurfaced in the 20th century with the photoelectric effect. In 1905, Albert Einstein explained this effect by introducing the concept of light quanta or photons. Quantum particles are considered to have wave–particle duality.
Moreover, in another paper published the same month in 1905, Einstein made several observations on a then-thorny problem, the photoelectric effect. In this work he demonstrated that light can be considered as particles that have a "wave-like nature". Particles obviously do not need a medium to travel, and thus, neither did light.