When light shines on some substances, the electrical properties of the substances change, that is, light energy is converted into electrical energy. This photoelectric change phenomenon is collectively called photoelectric effect. This phenomenon was accidentally discovered by Hertz in the experimental study of Maxwell's electromagnetic theory in 1887. 1888, German physicist Holva confirmed that this was due to the appearance of charged bodies in the discharge gap. 1899, J. J. Tang Musun confirmed through experiments that the charged body is an electron flow similar to cathode rays. During the period of1899 ——1902, Learnard made a systematic study of photoelectric effect, and named it photoelectric effect. 1905, Einstein explained the photoelectric effect comprehensively with the light quantum theory in his article "An enlightening viewpoint on the generation and transformation of light". 19 16 years, American scientist Millikan proved Einstein's theoretical explanation and optical quantum theory through accurate quantitative experiments.
photoeffect
1905, Einstein put forward the photon hypothesis and successfully explained the photoelectric effect, so he won the 192 1 year Nobel Prize in Physics. When light irradiates a metal, the electrical properties of this substance will change. This photochromic phenomenon is collectively called photoelectric effect. The photoelectric effect can be divided into photoelectron emission, photoconductive effect and photovoltaic effect. The former phenomenon occurs on the surface of an object, which is also called external photoelectric effect. The latter two phenomena occur inside the object, which is called internal photoelectric effect. Hertz discovered the photoelectric effect in 1887, and Einstein was the first to successfully explain the photoelectric effect (the effect that a metal surface emits electrons under the action of light irradiation, and the emitted electrons are called photoelectrons). Only when the wavelength of light is less than a certain critical value can electrons be emitted, that is, the limit wavelength, and the corresponding frequency of light is called the limit frequency. The critical value depends on the metal material, and the energy of emitted electrons depends on the wavelength of light, which has nothing to do with the intensity of light and cannot be explained by the fluctuation of light. And the fluctuation of light is also contradictory, that is, the instantaneity of photoelectric effect. According to the fluctuation theory, if the incident light is weak and the irradiation time is long, the electrons in the metal can accumulate enough energy and fly out of the metal surface. But the fact is that as long as the frequency of light is higher than the limit frequency of metal, no matter the brightness of light, the generation of photons is almost instantaneous, no more than ten MINUS nine seconds. The correct explanation is that light must be composed of strictly defined energy units (i.e. photons or optical quanta) related to wavelength. In the photoelectric effect, the emission direction of electrons is not completely directional, but most of them are emitted perpendicular to the metal surface, regardless of the irradiation direction. Light is electromagnetic wave, but light is an orthogonal electromagnetic field with high frequency oscillation, and its amplitude is very small, which will not affect the emission direction of electrons. brief introduction
The photoelectric effect can be divided into photoelectron emission, photoconductive effect and photovoltaic effect. The former phenomenon occurs on the surface of an object, which is also called external photoelectric effect. The latter two phenomena occur inside the object, which is called internal photoelectric effect.
Hertz discovered the photoelectric effect in 1887, and Einstein was the first to explain it successfully. The effect of electrons emitted by metal surface under the action of light irradiation is called photoelectron. Only when the wavelength of light is less than a certain critical value can electrons be emitted, that is, the limit wavelength, and the corresponding frequency of light is called the limit frequency. The critical value depends on the metal material, and the energy of emitted electrons depends on the frequency of light, which has nothing to do with the intensity of light and cannot be explained by the fluctuation of light. And the fluctuation of light is also contradictory, that is, the instantaneity of photoelectric effect. According to the fluctuation theory, if the incident light is weak and the irradiation time is long, the electrons in the metal can accumulate enough energy and fly out of the metal surface. But the fact is that as long as the frequency of light is higher than the limit frequency of metal, no matter the brightness of light, the generation of photons is almost instantaneous, no more than ten MINUS nine seconds. The correct explanation is that light must be composed of strictly defined energy units (i.e. photons or optical quanta) related to wavelength.
In the photoelectric effect, the emission direction of electrons is not completely directional, but most of them are emitted perpendicular to the metal surface, regardless of the irradiation direction. Light is electromagnetic wave, but light is an orthogonal electromagnetic field with high frequency oscillation, and its amplitude is very small, which will not affect the emission direction of electrons.
The photoelectric effect shows that light has particle property. Accordingly, the most typical examples of light fluctuation are light interference and diffraction.
As long as the frequency of light exceeds a certain limit frequency, photoelectrons will immediately escape from the metal surface irradiated by light, resulting in photoelectric effect. When a closed circuit is added outside the metal and a forward power supply is added, all these escaped photoelectrons reach the anode, forming a so-called photocurrent. When the incident light is constant, the photocurrent will increase by increasing the DC voltage at the two poles of the photovoltaic cell and improving the kinetic energy of photoelectrons. However, the photocurrent will not increase indefinitely. Limited by the number of photoelectrons, there is a maximum value, which is the saturation current. Therefore, when the incident light intensity increases, according to the photon hypothesis, the incident light intensity (that is, the light energy passing through the unit vertical area in unit time) depends on the number of photons passing through the unit vertical area in unit time, and the number of photons passing through the metal surface in unit time also increases, so the number of collisions between photons and electrons in the metal also increases, so the number of photoelectrons escaping from the metal surface in unit time also increases, and the saturation current also increases.