Philipp Eduard Anton von Lénárd discovered the important law of photoelectric effect through experiments.
Albert Einstein put forward the correct theoretical mechanism.
1839, Alexandre Becquerel, who was only 19 years old, discovered the photovoltaic effect while helping his father to study the effect of light wave irradiation on electrolytic cells.
Although this is not an optical effect, it plays a great role in revealing the close relationship between the electrical properties of substances and light waves.
Willoughby Smith tested the high-resistance characteristics of the selenium drum in an underwater cable-related task of 1873, and found that it has photoconductivity, that is, the light beam irradiated on the selenium drum will increase its conductance.
Heinrich hertz
During the period of 1887, German physicist heinrich hertz observed the photoelectric effect and the emission and reception of electromagnetic waves in the experiment.
There is a spark gap in the Hertz transmitter, which can generate and emit electromagnetic waves by generating sparks.
There is a coil and a spark gap in the receiver. Whenever the coil detects electromagnetic waves, sparks will appear in the spark gap.
Because the spark is not very bright, in order to observe the spark more easily, he put the whole receiver in an opaque box.
He noticed that the maximum spark length was thus reduced.
In order to find out the reason, he removed a part of the box and found that the opaque plate between the receiver spark and the transmitter spark caused this shielding phenomenon.
If glass is used as a partition, this shielding phenomenon will also occur, but it will not happen in time.
He used a timely prism to decompose light waves by wavelength, and after carefully analyzing the shielding behavior of light waves of each wavelength, he found that ultraviolet light caused photoelectric effect.
Hertz published these experimental results in the Yearbook of Physics, and he didn't do any further research on this effect.
The discovery that ultraviolet light incident on the spark gap helps to generate sparks immediately aroused the curiosity of physicists, including William Harva, Augusto Righi, Alexander Storey, and so on.
They made a series of investigations on the influence of light waves on charged objects, especially ultraviolet rays.
These investigations have confirmed that if the zinc metal surface that has just been cleaned is negatively charged, it will quickly lose this negative charge under ultraviolet irradiation, no matter how much it is; If neutral zinc metal is irradiated by ultraviolet rays, it will be positively charged quickly, and electrons will escape into the gas around the metal. If strong winds blow on metals, the number of metals with positive charges will increase greatly.
Johann elster and Hans Geitel first developed the first practical photoelectric vacuum tube, which can be used to measure irradiance.
Astor and Geitel used it to study the effect of light waves on charged objects, and achieved great results.
They arranged various metals according to the discharge capacity of photoelectric effect from large to small: rubidium, potassium, sodium-potassium alloy, sodium, lithium, magnesium, thallium and zinc.
For copper, platinum, lead, iron, cadmium, carbon and mercury, the photoelectric effect caused by ordinary light waves is very small and no effect can be measured.
The arrangement order of the above metals is the same as that of Alessandro Volta, and the more positively charged the metal, the greater the photoelectric effect.
Experimental device of photoelectric effect for measuring charge-mass ratio of particles.
At that time, all kinds of experiments to study Hertz effect were accompanied by the phenomenon of "photoelectric fatigue", which made the research more complicated.
Photoelectric fatigue refers to the gradual attenuation of photoelectric effect observed from clean metal surface.
According to the research results of Holvax, ozone plays a very important role in this phenomenon.
However, other factors, such as oxidation, humidity, polishing methods, etc. , must be taken into account.
During the period from 1888 to 189 1, Stoletov completed many experiments and analysis on photoelectric effect.
He designed an experimental device, which is especially suitable for quantitative analysis of photoelectric effect.
With the help of this experimental device, he found the direct ratio between irradiance and induced photocurrent.
In addition, Stoletov and Rigi also studied the relationship between photocurrent and air pressure. They found that the lower the air pressure, the greater the photocurrent until the optimal air pressure is reached. Below this optimum air pressure, the lower the air pressure, the smaller the photocurrent becomes.
Joseph Tang Musun 1897 said in a speech at the Royal Society on April 30th, 1997 that he found that the transmission ability of cathode ray in air was far more than that of ordinary atomic particles by observing the fluorescence irradiance caused by cathode ray in Crookes tube.
Therefore, he argued that cathode rays were composed of negatively charged particles, which were later called electrons.
Shortly thereafter, he measured the charge-mass ratio of cathode ray particles by observing the deflection of cathode ray under the action of electric field and magnetic field.
1899, he irradiated zinc metal with ultraviolet rays, and the charge-to-mass ratio of emitted particles was 7.3× 10emu/g, which was roughly consistent with the cathode ray particle value of 7.8× 10emu/g measured in previous experiments.
He therefore correctly concluded that these two kinds of particles are the same kind of particles, that is, electrons.
He also measured the negative charge contained in the particles.
From these two data, he successfully calculated the mass of electrons: about one thousandth of the mass of hydrogen ions.
Electrons were the smallest particles known at that time.
Hungarian physicist Philipp Eduard Anton von Lénárd
1900, Philipp Eduard Anton von Lénárd discovered that ultraviolet rays can cause gas ionization.
Because this effect widely occurs in air several centimeters wide, it produces many large positive ions and small negative ions. This phenomenon is naturally interpreted as the photoelectric effect of solid particles or liquid particles in gas, which is Tom Musun's interpretation of this phenomenon.
1902, Leonard released several important experimental results about photoelectric effect.
First, by changing the distance between the ultraviolet light source and the cathode, he found that the number of photoelectrons emitted by the cathode is directly proportional to the incident irradiance per unit time.
Secondly, using different substances as cathode materials, we can see that the photoelectrons emitted by each substance have their specific maximum kinetic energy (maximum velocity), in other words, the maximum kinetic energy of photoelectrons is related to the spectral composition of light waves.
Thirdly, by adjusting the voltage difference between cathode and anode, he observed that the maximum kinetic energy of photoelectrons is proportional to the cut-off voltage and has nothing to do with irradiance.
Since the maximum velocity of photoelectrons has nothing to do with irradiance, Leonard believes that light waves have not given these electrons any energy, and these electrons already have this energy. Light wave acts as a trigger, which is Leonard's famous "trigger hypothesis".
At that time, the trigger hypothesis was generally accepted as the mechanism of photoelectric effect in academic circles.
However, this assumption has encountered some serious problems. For example, if an electron has kinetic energy after escaping from the bond and emitting in an atom, heating the cathode should give it more kinetic energy, but physicists have not measured any different results in the experiment.
The heroic Einstein published six epoch-making papers in 1905 (the year of Einstein's miracle).
1905, Einstein published a paper "Preliminary Views on the Generation and Transformation of Light", which gave another explanation to the photoelectric effect.
He described the light beam as a set of discrete quanta, now called photons, rather than continuous fluctuations.
Einstein gave another explanation to Max Planck's Planck relation discovered in his previous research on blackbody radiation: the photon energy with a frequency of 0 is 0; Where the factor is Planck constant.
Einstein thought that the energy of each quantum that makes up a light beam is equal to the frequency multiplied by Planck constant.
If the photon frequency is greater than a certain limit frequency, the photon has enough energy to make an electron escape, resulting in photoelectric effect.
Einstein's exposition explains why the energy of photoelectrons is only related to frequency, but not to irradiance.
Although the irradiance of the beam is very weak, as long as the frequency is high enough, some high-energy photons will be generated, which will promote the bound electrons to escape.
Although the irradiance of the beam is very strong, if the frequency is lower than the limit frequency, no high-energy photons can be given to promote the escape of bound electrons.
Einstein's argument is imaginative and persuasive, but it is strongly resisted by academic circles because it contradicts james maxwell's light wave theory, which has been proved by rigorous theoretical tests and accurate experiments. It can't explain the refraction and coherence of light waves, and more generally, it contradicts the "infinite separability hypothesis" of energy in physical systems.
Even after the experiment proved that Einstein's photoelectric effect equation was correct, the strong resistance continued for many years.
Einstein's discovery opened the door to quantum physics. Einstein won the 192 1 Nobel Prize in Physics for his "achievements in theoretical physics, especially the discovery of the law of photoelectric effect".
The picture shows the relationship between the maximum energy and frequency obtained from Millikan photoelectric effect experiment.
The vertical axis is the cut-off voltage that can prevent the maximum energy photoelectron from reaching the anode, P is the work function, and PD is the potential difference.
Einstein's paper quickly attracted the attention of American physicist robert millikan, but he also disagreed with Einstein's theory.
In the next ten years, he spent a lot of time doing experiments to study the photoelectric effect.
He found that the maximum photoelectron energy would not increase with the increase of cathode temperature.
He also confirmed that photoelectric fatigue is caused by impurities produced by oxidation. If the clean cathode can be kept in a high vacuum, this phenomenon will not happen.
19 16 years, he confirmed the correctness of Einstein's theory and directly calculated Planck's constant by photoelectric effect.
Millikan was awarded the 1923 Nobel Prize in Physics for his work on elementary charge and photoelectric effect.
According to the wave-particle duality, the photoelectric effect can also be analyzed by the concept of wave, without the concept of photon at all.
Willis lamb and Marlan Scully proved this theory in 1969.