Einstein is a great scientist who is most familiar to everyone, and his popularity is only increasing, because all the predictions left by Einstein were verified in recent years with the development of science and the progress of observation methods. The publication of the first photo of human black holes on April 1th once again proved Einstein to be correct. Many friends are most familiar with Einstein's achievements in space-time and gravity, but Einstein's achievements in quantum mechanics are also enormous. His? Light quantum theory? It not only explains the photoelectric effect, but also lays the foundation for quantum mechanics. Light quantum also directly leads scientists to discuss the nature of light? The wave-particle duality of light turned the whole scientific community upside down in the 2th century.
Hertz discovers photoelectric effect
In p>1887, during a series of experiments to show the existence of electromagnetic waves, German physicist Heinrich? The photoelectric effect was first observed by Heinrich Hertz. He inadvertently noticed that between two metal balls, if one of them is irradiated by ultraviolet light, the spark between the two metal balls will become brighter. What does he think of this? A brand-new and very puzzling phenomenon? After months of research, I couldn't come up with any explanation, but I thought, of course, wrongly, that this phenomenon was limited to the use of ultraviolet light. It is a pity that Hertz died young at the age of 36 in 1894 without waiting for this phenomenon to be explained.
Later, Hertz's former assistant Philip? In 192, Philipp Lenard took the mystery surrounding the photoelectric effect a step further. When he put two pieces of metal into a glass tube and exhausted the air, he found that this phenomenon would also happen in a vacuum. Leonard found that when the wires on each metal sheet are connected to a battery, if a metal sheet is irradiated by ultraviolet light, a current will flow. This photoelectric effect is explained by the release of electrons from the irradiated metal surface. When ultraviolet light is irradiated on a metal sheet, some electrons gain enough energy to escape from the metal sheet and pass through the space to another metal sheet, thus completing an energy generation. Photocurrent The circuit. However, Leonard also found some phenomena that contradict the existing physics. It's Einstein's turn and his quantum of light.
Einstein and his quantum of light
The intensity of light determines the number of electrons kicked out. It is expected that the number of electrons released from the metal surface will remain unchanged and the energy of each electron will increase when the intensity of the beam is increased to make it brighter. But Leonard found the opposite: more electrons were released, but the energy carried by each electron did not increase. Einstein's answer to quantum theory is concise and neat: if light is made up of quanta, then strengthening the intensity of the beam means more quanta in the beam. When a more powerful beam hits the metal plate, the increase in the number of light quantum leads to a corresponding increase in the number of electrons released.
the energy of the released electrons is related to the frequency of light. Leonard's second peculiar discovery is that the released electrons are not limited by the intensity of the beam, but by the frequency of the beam. Einstein has a ready-made answer to this. Since the quantum energy of light is proportional to the frequency of light, the quantum energy of red light (low frequency) is lower than that of blue light (high frequency). Changing the color (frequency) of light will not change the number of quanta in the same intensity beam. Therefore, no matter what color the light beam is, the same number of quanta will release the same number of electrons when they hit the metal plate. However, because light with different frequencies is composed of quanta with different energies, the energy of the released electrons will be larger or smaller, depending on the light used. When ultraviolet light is used, the maximum kinetic energy of electrons is greater than that released by red quantum.
work function of electrons? There is another puzzling phenomenon in the work equation. Any particular metal has a lowest or? Critical frequency? Below this frequency, no electrons will be released at all, no matter how long or how strong the metal is irradiated. However, once this critical point is crossed, electrons will be released, no matter how weak the beam is. Because Einstein introduced a new name? Work function? That is, the concept of work function, so his theory of light quantum gives the answer again.
Einstein regarded photoelectric effect as a result, that is, electrons need to get enough energy from light quantum to overcome the force that leaves it on the metal surface before they can escape, and photoelectric effect is the result. What Einstein called it? Work function? , is the minimum energy required for electrons to escape from the metal surface, which varies with different metals. If the frequency of light is too low, there is not enough energy for electrons to break through the binding force that fixes it in metal.
Einstein compiled all this into a simple equation: the maximum kinetic energy of an electron released from a metal surface is equal to the energy of the light quantum it absorbs minus the work function. Using this equation, Einstein predicted that if the corresponding relationship between the maximum kinetic energy of electrons and the frequency of light used was drawn as a graph, the graph would be a straight line, starting from the critical frequency of metals. The inclination of this line, no matter what kind of metal is used, will always be exactly equal to Planck's constant H. This is Einstein's explanation of photoelectric effect, but the theory needs experimental verification, so some experimental physicists specialize in verifying the amazing theory of theoretical physicists.
the photoelectric effect equation is verified
American experimental physicist Robert? Millikan spent 1 years of his life testing Einstein's photoelectric effect equation in 195. It turned out that Ince was right and absolutely correct. About Einstein? He's right? I have heard this sentence many times now. The release of the black hole photos on April 1th once again proves that Einstein is right. This great man has gone further and further on the right road.
In a word, it can be said that there are a lot of problems in modern physics, and among some important problems, there is hardly any Einstein who has not played a remarkable role. In 1921, Einstein was awarded the belated Nobel Prize in Physics, which made it clear that it was the law of photoelectric effect described in the formula awarded to him, rather than his explanation based on the quantum theory of light. After all, his quantum theory of light was too subversive to be accepted by physicists. However, this has directly triggered the debate among scientists on the nature of light, and the door of quantum mechanics will gradually open.