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Photoelectric Effect
In 1905, Albert Einstein put forward the hypothesis of photon, successfully explained the photoelectric effect, and therefore won the Nobel Prize in Physics in 1921. Light shining on a metal causes a change in the electrical properties of the substance. This kind of light change electrification phenomenon is collectively known as the photoelectric effect.
The photoelectric effect is divided into photoelectron emission, photoconductive effect and photovoltaic effect. The former phenomenon occurs on the surface of the object, also known as the external photoelectric effect.
The latter two phenomena occur inside the object, known as the internal photoelectric effect. Hertz discovered the photoelectric effect in 1887, Einstein was the first to successfully explain the photoelectric effect metal surface under the action of light irradiation emission of electrons, the emission of electrons called photoelectrons.
The wavelength of light is less than a certain critical value can be emitted electrons, that is, the limiting wavelength, the corresponding frequency of light is called the limiting frequency. The critical value depends on the material of the metal, and the energy of the emitted electrons depends on the wavelength of the light and is independent of the intensity of the light, which cannot be explained by the volatility of light.
There is also a contradiction with the volatility of light, that is, the photoelectric effect of the transient, according to the theory of volatility, if the incident light is weaker, the irradiation time to be a little longer, the electrons in the metal in order to accumulate enough energy to fly out of the metal surface. But the fact is, as long as the frequency of light is higher than the limiting frequency of the metal, the brightness of the light, no matter how strong or weak, the production of photons is almost instantaneous, no more than ten minus nine times the square second.
The correct interpretation is that light must consist of strictly defined units of energy related to wavelength, i.e., photons or light quanta. In the photoelectric effect, the electrons are not shot in a perfectly directional direction, but mostly perpendicular to the surface of the metal, independent of the direction of the light.