Generally speaking, photoelectric effect means that when a light beam irradiates a metal surface, it will emit electrons. This phenomenon is very strange. At first, electrons were bound by atoms on the metal surface. Strangely, once irradiated by some light, these electrons begin to be restless and want to escape from the bondage of atoms. Because the protagonist of this phenomenon is the "second boss" of light and electronics, everyone calls it photoelectric effect.
More interestingly, this photoelectric effect is still very naughty. It does not mean that as long as there is light irradiation on the metal surface, electrons will definitely be generated. In order to realize it, it is necessary to put forward requirements for the irradiated light.
It is found that for the same metal, under the same conditions, light energy can't knock electrons out of the metal surface, which depends on the frequency of light (in visible light, from purple to blue to green to yellow to red, the frequency decreases gradually, with the highest frequency of purple light and the lowest frequency of red light). Even more amazing is that light with higher frequency can produce electrons with higher energy, while light with lower frequency can't produce electrons at all.
So some people think, what if we play with very strong low-frequency light (red) or very weak high-frequency light (purple)? It turns out that electrons only recognize frequency but not intensity. Even the strongest low-frequency light cannot beat out half an electron, and the weakest high-frequency light can beat out electrons, but in the case of high-frequency light, changing the intensity of light can change the number of electrons.
Summary: When some light strikes the metal surface, the metal surface can emit electrons, which is the photoelectric effect. Whether light can hit electrons on the same metal surface depends on the frequency of light rather than the intensity of light.
Heinrich hertz is a talented German physicist. His teachers are the famous Kirchhoff and Helmholtz. Hertz has made great contributions in the field of electromagnetism, so the unit of frequency Hertz is named after him. The unexpected encounter between Hertz and photoelectric effect began with Maxwell equations and electromagnetic waves.
/kloc-in the 9th century, the great Maxwell summed up the four equations of electric field gauss law, magnetic field gauss law, Faraday electromagnetic induction law and Maxwell-Ampere law into Maxwell group, expounded that changing magnetic field produces electric field and changing electric field produces magnetic field, and predicted the existence of electromagnetic wave in theory, which unified electricity and magnetism as never before.
But Maxwell only proved the existence of electromagnetic waves perfectly in theory, but did not really prove the existence of electromagnetic waves. Next, it is Mr. Hertz's turn to appear as one of the protagonists of this article. Confirm that the existence of electromagnetic waves is none other than hertz. Hertz confirmed the existence of electromagnetic waves in his laboratory, which capped the establishment of electromagnetism, but it was in the experiment of proving the existence of electromagnetic waves that Hertz unexpectedly opened the door of quantum mechanics and discovered the existence of photoelectric effect.
In Hertz's experiment to prove the existence of electromagnetic waves, Hertz found that when there is light on the metal receiver, electric sparks are more likely to appear, which is the original version of photoelectric effect. However, this phenomenon did not attract enough attention from Hertz, who mentioned it in his paper, but he did not study it carefully. Unfortunately, Hertz didn't have enough opportunities to study it. Hertz died at the age of 36. What Hertz didn't know was that his discovery actually kicked the door of quantum mechanics. People often think that if God can make Hertz live longer, maybe the development of quantum mechanics can be advanced.
When it comes to Einstein, people may hear the special relativity and general relativity most, but the explanation of photoelectric effect is actually Einstein's classic, which won Einstein the Nobel Prize in physics.
As mentioned earlier, in the photoelectric effect, electrons only recognize the frequency of light, but not the intensity of light. In the cognition at that time, light was a wave, and the intensity of the wave represented energy. It can be said that because electrons are bound to the orbit by atoms, the higher the intensity and energy, the easier it should be to type out. But in fact, if the frequency of light is low, no matter how strong the intensity is, electrons can't be typed, that is to say, the frequency of light determines whether electrons can be typed, and the intensity of light determines the number of electrons typed. This made scientists at that time very puzzled and puzzled until the genius Einstein was born.
Einstein's way of solving this problem is a little different from others. He borrowed Mr. Planck's quantum hypothesis (Planck's hypothesis is that when a black body absorbs or emits energy, it is not continuous, but divided into several parts of energy, the size of which is equal to Planck's constant multiplied by frequency, and this part of energy is called quantum).
Photoelectric effect, the higher the frequency, the easier it is to hit electrons; The energy of a single quantum is equal to Planck constant h multiplied by frequency v, and the higher the frequency, the higher the energy of a single quantum.
Between the crackles, Einstein suddenly saw something. The higher the frequency, the higher the energy of a single quantum. So, what if light is not distributed continuously, but a quantum? All problems are solved instantly, and the frequency is increased. The higher the energy of a single photon, the easier it is to hit an electron. The energy of a single photon is greater than the binding energy of metal atoms to electrons, and electrons can be hit. This just explains why frequency determines whether electrons can be typed. Increasing the intensity of light corresponds to increasing the number of light quanta. The more photons there are, the more electrons are produced, and the intensity determines the number of electrons produced. Well, gentlemen, the photoelectric effect is now perfectly explained.
Then Einstein wrote an equation according to this idea. On the left side of the equal sign is the kinetic energy of knocking out electrons, and on the right side of the equal sign is the energy of a single photon minus the minimum energy required to knock out electrons.
We should note that although Einstein successfully explained the photoelectric effect, there is a premise, and this premise is Planck's quantum hypothesis. Einstein quantized light here, thinking that light is a kind of light quantum. At that time, light was regarded as a wave, which was continuous, while quantum was discontinuous. Einstein's move is undoubtedly a challenge to the original classical physical system, a genius idea, and a seemingly deviant idea.
In fact, after Planck put forward the quantum hypothesis, Planck himself didn't quite believe what quantum was and whether it existed. Planck himself is not sure. Einstein explained the photoelectric effect with quantum theory, which is a pioneering work. There is no doubt that Einstein successfully explained the photoelectric effect by using quantum theory, which is undoubtedly a great affirmation of the correctness of quantum mechanics.
The successful explanation of photoelectric effect by quantum theory has injected great impetus into the development of quantum mechanics, which is the further development of quantum theory and a milestone in the establishment of quantum theory. This makes people formally put quantum theory on the table for crazy discussion. After that, quantum theory entered a period of rapid development, and Schrodinger, De Broglie, Heisenberg and Bonn opened the golden age of quantum mechanics.
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4 Zeng Jinyan. Quantum mechanics [M]. 1990.