Briefly

photoelectric effect is the emission of electrons by a substance under the action of light (and, generally speaking, any electromagnetic radiation). In condensed substances (solid and liquid), external and internal photoelectric effects are distinguished.

Laws of the photoelectric effect:

1st law of photoelectric effect: the number of electrons ejected by light from the surface of a metal per unit time at a given frequency is directly proportional to the light flux illuminating the metal.

This hypothesis is known as the light beam model. In a collision, it loses some or all of its energy. This is done in the generator which has. Transmission of electromagnetic waves When connected to a transmitter. The passage of an atom from the excited state to the ground state is carried out. Spectra, radiation and energy Radiation is the propagation of energy by means of particles or waves in space. Radiation can be defined as: a conductive element of energy: electromagnetic radiation.

Nelson Luis Reyes Marquez Rainbow interference = refraction of soap bubble interference Superposition principle When two or more waves overlap. Biophysics Bachelor of Biology Imaging and optical instruments. The image above shows a schematic of an experiment setup showing the photoelectric effect. This effect occurs when one quantum of light is absorbed by a metal, and all of its energy is transferred to one electron. The basic mechanism is illustrated by the equation.

2nd law of photoelectric effect: maximum kinetic energy of electrons ejected by light increases linearly with the frequency of light and does not depend on its intensity.

3rd law of photoelectric effect: for each substance there is a red border of the photoelectric effect, that is, the minimum frequency of light ν 0 (or maximum wavelength λ 0 ), at which the photoelectric effect is still possible, and if ν < ν 0 , then the photoelectric effect no longer occurs.

Where γ is the incident photon. Increasing the intensity will increase the number of photons reaching the metal, and in doing so, the number of electrons being ejected. There will be more intense photovoltaic current, but the individual energy of each electron will be the same. If the energy of the photon is greater than the energy that holds the electron in the metal, then the electron is released, and the excess energy is released in the form of the kinetic energy of a free electron.

Provides energy conservation. Let's say that for a given potential difference between the plates, a certain intensity and frequency of the incident light has a photoelectric current. Note that the figure shows that there is a minimum light frequency for the photoelectric effect. A beam of light with this minimum frequency, called the cutoff frequency, contains photons with the minimum energy to expel electrons from the metal at an almost zero ejection velocity. And light is rarer than it can produce photoelectrons, no matter how intense the backlight is.

Electromagnetic radiation is a stream of individual quanta (photons) with energy hν each, where h is Planck's constant. With the photoelectric effect, part of the incident electromagnetic radiation is reflected from the metal surface, and part penetrates into the surface layer of the metal and is absorbed there. Having absorbed a photon, the electron receives energy from it and, doing the work function, leaves the metal: hν = A out + W e, where W e is the maximum kinetic energy that an electron can have when it leaves the metal.

Now can you calculate the Kingdom work function? Go back to the virtual experiment and check it out! Although intuition and experience have long supported the massless neutrino, it is important to ask if this hypothesis is correct. There are some methods for checking the neutrino mass.

According to the Standard Model, the absolute value of the helicity of a particle with zero mass is constant. Indeed, since the value of angular momentum is constant and it works with potentially relativistic particles, the only way to obtain constant helicity is to impose a constant velocity. Finally, the particle in question must have zero mass in order to constantly have a constant velocity.

From the law of conservation of energy, when light is represented in the form of particles (photons), Einstein's formula for the photoelectric effect follows:

hν = A out + E k

A out is the work function (the minimum energy required to remove an electron from a substance),

E k is the kinetic energy of the emitted electron (depending on the velocity, it can be calculated as the kinetic energy relativistic particle, and no),

Measure helicity ½ for the antineutrino product. Likewise, all neutrinos produced by the reaction. So if maximum energy emitted electrons is equal to this cutoff energy, the electron antineutrino mass is zero. On the other hand, if the antineutrino has a nonzero mass, then the last part of the decay energy is carried away by the last. Which corresponds to the reduction of the tail of the energy spectrum of the emitted electrons. On the other hand, one cannot say with certainty that neutrinos have zero mass by this method, because one can always assume that neutrinos have a mass that is too weak to be detected by instruments.

ν is the frequency of the incident photon with energy hν,

h is Planck's constant.

in detail

The photoelectric effect is the phenomenon of ejection of electrons from solid and liquid bodies under the influence of light.

Discovered the photoelectric effect Heinrich Hertz(1857 - 1894) in 1887 year. He noticed that the jumping of a spark between the balls of the spark gap is greatly facilitated if one of the balls is illuminated with ultraviolet rays.

Another way to determine if neutrinos are mass is to oscillate them. By analogy with a mixture of kaons. It can be assumed that the three neutrino flavors are linear combinations of mass eigenstates, i.e. If the hypothesis of mixtures of mass eigenstates is good, then neutrino flavor oscillations can occur.

It should be noted that these results refer to propagation in a vacuum. To make these results useful for experiment, it may be convenient to rewrite them in terms of spatial rather than temporal parameters. Which leads to the desired result.

Then in 1888-1890 1990s, he studied the photoelectric effect Alexander Grigorievich Stoletov(1839 – 1896).

He established that:

  • ultraviolet rays have the greatest effect;
  • with an increase in the luminous flux, the photocurrent increases;
  • the charge of particles emitted from solid and liquid bodies under the action of light is negative.

In parallel with Stoletov, the photoelectric effect was studied by a German scientist Philip Lenard(1862 – 1947).

Suppose we have a beam of neutrino electrons. So where the beam comes from, we have. One can then calculate what kind of neutrino flavor will be observed for any position. In the last equation, we took this term into account. Therefore, we have a phase change defined as follows.

With mass expressed in eV and energy in GeV. To simplify the problem, we can assume that the mixture has only two eigenstates. It is possible to experimentally measure the consequences of changing the taste of neutrinos. It should be noted that other models explain the fluctuation in taste without involving the neutrino mass. However, the one studied here remains the simplest and can be considered relatively fair.

They established the basic laws of the photoelectric effect.

Before formulating these laws, let us consider a modern scheme for observing and studying the photoelectric effect. She is simple. Two electrodes (cathode and anode) are soldered into the glass cylinder, to which voltage U is applied. In the absence of light, the ammeter indicates that there is no current in the circuit.

When the cathode is illuminated with light, even in the absence of voltage between the cathode and the anode, the ammeter shows the presence of a small current in the circuit - photocurrent. That is, the electrons that have flown out of the cathode have some kinetic energy and reach the anode "on their own".

This is a purely energetic elemental physique, rather than a further division, and supports other fundamental units of physics such as electrons, ions, and finally nuclei. When heated to enough high temperature it emits radiation whose spectral distribution no longer depends on its shape, on its nature, or on other specific properties of the body, but only on its absolute temperature. And that they represent the smallest amount of energy that an oscillator of a given frequency can exchange with environment that surrounds her.

As the voltage increases, the photocurrent increases.

The dependence of the photocurrent on the voltage between the cathode and the anode is called the current-voltage characteristic.

It has the following form. At the same intensity monochromatic light as the voltage increases, the current first increases, but then its growth stops. Starting from a certain value of the accelerating voltage, the photocurrent ceases to change, reaching its maximum (at a given light intensity) value. This photocurrent is called the saturation current.

Einstein found that it was impossible to explain the energy associated with blackbody radiation through quivers, but breaking them up became a fundamental concept generalized to any type of radiation in existence. In summary, we can say that when a metal surface hits due to high enough frequency radiation, it releases electrons.

The explanation for this phenomenon is that the energy of the incident radiation is converted into the kinetic energy of the struck electrons, which therefore move. However, they do not always separate from their orbits, since the kinetic energy must be greater than the force holding the electrons bound to the atom.

To "lock" the photocell, that is, reduce the photocurrent to zero, it is necessary to apply a "blocking voltage". In this case, the electrostatic field does work and slows down the emitted photoelectrons

This means that none of the electrons emitted from the metal reaches the anode if the anode potential is lower than the cathode potential by a value.

The photoelectric effect is a phenomenon that does not occur only in metals, but in them it is more obvious: it occurs whenever an elemental material system, an atom or a molecule or a crystal is embedded by electromagnetic radiation with a sufficiently high energy.

From the study of this phenomenon, we have obtained important results that can be schematized in three main points. There is photoelectric emission only if the frequency of the incident radiation is higher than the value of the photoelectric threshold. The kinetic energy of the emitted electrons depends on the frequency of the incident radiation, and not on its intensity.

The experiment showed that when the frequency of the incident light changes, the starting point of the graph shifts along the stress axis. It follows from this that the magnitude of the blocking voltage, and, consequently, the kinetic energy and maximum velocity of the emitted electrons, depend on the frequency of the incident light.

The first law of the photoelectric effect. The value of the maximum velocity of the emitted electrons depends on the frequency of the incident radiation (increases with increasing frequency) and does not depend on its intensity.

The number of electrons emitted per unit of time increases as the intensity of the incident electromagnetic radiation increases. He believed that the kinetic energy gained by the electrons had to be equivalent to the energy possessed by the photons.

To summarize the differences between classical and quantum theory, one can resort to a comparison between the quantities that are considered in each of the two categories, i.e. continuous in classical theory, and discrete in quantum. According to classical physics, some quantities, such as the emission or absorption of the radiation of a substance, belonged to the group of continuous ones, and according to Planck's new theories, these quantities are characterized by jumps to certain values, i.e. the multiplicity of how much elemental energy; so we can say that with the new theories we have gone from a world that is only interpreted in a continuous way to one that is interpreted even discretely.

If we compare the current-voltage characteristics obtained at different intensities (in Figures I 1 and I 2) of incident monochromatic (single-frequency) light, we can notice the following.

First, all current-voltage characteristics originate at the same point, that is, at any light intensity, the photocurrent vanishes at a specific (for each frequency value) retarding voltage. This is another confirmation of the fidelity of the first law of the photoelectric effect.

According to some researchers quantum mechanics, our own reality doubles every time a particle has the ability to behave differently, giving life to two parallel universes: in one particle behaves in one direction, and the other vice versa. Forming a double division of all options. In short, it seems that, having become accustomed to the idea that neither the Earth nor our galaxy is at the center of creation, we should soon come to terms with the fact that we do not belong to the only universe that exists.

If gravity were a little stronger, stars would burn their nuclear fuel in less than a year. If, instead, the force holding atoms together was weaker, stars would not even exist. In short, life on Earth is the result of such special circumstances and conditions that are so limited that they are considered an extremely unlikely event in themselves.

Secondly. With an increase in the intensity of the incident light, the nature of the dependence of the current on the voltage does not change, only the magnitude of the saturation current increases.

The second law of the photoelectric effect. The value of the saturation current is proportional to the value of the luminous flux.

When studying the photoelectric effect, it was found that not all radiation causes a photoelectric effect.

However, there is a way to explain such an astonishing series of coincidences: to recognize that entire universes are continually being formed, each of which has quite a random stats. This would increase the statistical probability that, among many, the universe could be born with the right conditions to generate man as he is.

According to his theory, when everyone else is born from the same universe, the physical laws are slightly modified, as they are for living beings. Thus, there are universes that are born with hostile laws and eventually extinguish. This original idea is based on the observation of quantum mechanics that there are microscopic phenomena in which a particle acts as if it interferes with an invisible but real "analogue". If these small particles have an analogue, then it follows from them that even the largest objects have an analogy of some kind.

The third law of the photoelectric effect. For each substance there is a minimum frequency (maximum wavelength) at which the photoelectric effect is still possible.

This wavelength is called the "red border of the photoelectric effect" (and the frequency - corresponding to the red border of the photoelectric effect).

5 years after the appearance of the work of Max Planck, Albert Einstein used the idea of ​​the discreteness of light emission to explain the patterns of the photoelectric effect. Einstein suggested that light is not only emitted in batches, but also propagated and absorbed in batches. This means that the discreteness of electromagnetic waves is a property of the radiation itself, and not the result of the interaction of radiation with matter. According to Einstein, a radiation quantum resembles a particle in many ways. A quantum is either completely absorbed or not absorbed at all. Einstein imagined the escape of a photoelectron as the result of a collision of a photon with an electron in a metal, in which all the energy of the photon is transferred to the electron. So Einstein created quantum theory light and, based on it, wrote an equation for the photoelectric effect:

And for the proponents of this theory, these two realities are not alternatives, but both occur. It is possible that there are many other universes, and between other worlds and ours there are exchanges, separations and intersections, which, perhaps, one day they will be able to reveal.

But for now, this is just a suggestive hypothesis. Therefore, this long-term limit photoelectric effect is a direct measure of the work function of an electron from a metal. Increasing the radiation intensity does not increase the energy of the emitted electrons, but only increases their number. In other words: for each type of radiation there is one value of the braking voltage, depending only on the color of the light, i.e. on its frequency, but not on its intensity. This fact can only be explained by the assumption that quantum nature electromagnetic wave.

This equation explained everything experimentally established laws photoelectric effect.

  1. Since the work function of an electron from a substance is constant, then, with increasing frequency, the speed of electrons also increases.
  2. Each photon knocks out one electron. Therefore, the number of ejected electrons cannot be more number photons. When all the ejected electrons reach the anode, the photocurrent stops growing. As the light intensity increases, so does the number of photons incident on the surface of matter. Consequently, the number of electrons that these photons knock out increases. In this case, the saturation photocurrent increases.
  3. If the energy of photons is only enough to perform the work function, then the speed of the emitted electrons will be equal to zero. This is the "red border" of the photoelectric effect.

The internal photoelectric effect is observed in crystalline semiconductors and dielectrics. It consists in the fact that under the action of irradiation, the electrical conductivity of these substances increases due to an increase in the number of free current carriers (electrons and holes) in them.



This phenomenon is sometimes called photoconductivity.

The maximum kinetic energy that a particle must have to carry out impact ionization of a gas atom will be the closer to LIONIS, the smaller the mass of the particle compared to the mass of the atom. For an electron, this energy is less than for any ion.
The maximum kinetic energy that an electron inside a metal can have is insufficient for this.
The maximum kinetic energy of photoelectrons does not depend on the intensity of the incident light, but is determined, other things being equal, only by the frequency of the incident monochromatic light and increases with increasing frequency. This experimental (qualitative) fact was theoretically substantiated by A.
The maximum kinetic energy of photoelectrons is directly proportional to the frequency of the absorbed light and does not depend on its intensity.
The maximum kinetic energy of photoelectrons increases linearly with increasing frequency of monochromatic radiation that causes the photoelectric effect.
The maximum kinetic energy of an oscillator is equal to its maximum potential energy. This is obvious, since the oscillator has the maximum potential energy when the oscillating point is displaced to the extreme position, when its velocity (and, consequently, the kinetic energy) is equal to zero. The oscillator has the maximum kinetic energy at the moment of passing the point of equilibrium position (x 0), when potential energy equals zero.
The maximum kinetic energy of an oscillator is equal to its maximum potential energy. This is obvious, since the oscillator has the maximum potential energy when the oscillating point is displaced to the extreme position, when its velocity (and, consequently, the kinetic energy) is equal to zero. The oscillator has the maximum kinetic energy at the moment of passing the point of equilibrium position (x 0), when the potential energy is equal to zero.
The maximum kinetic energy of photoelectrons increases linearly with increasing frequency of light waves and does not depend on the power of light radiation.
The maximum kinetic energy of photoelectrons is proportional to the frequency of the absorbed light and does not depend on its intensity.
The maximum kinetic energy of a photoelectron is equal to the energy of the photon absorbed by it.
The maximum kinetic energy of an oscillator is equal to its maximum potential energy. This is obvious, since the oscillator has the maximum potential energy when the oscillating point is displaced to the extreme position, when its velocity (and, consequently, the kinetic energy) is equal to zero. The oscillator has the maximum kinetic energy at the moment of passing the point of equilibrium position (n: 0), when the potential energy is equal to zero.
Accordingly, the maximum kinetic energy Гmax is determined by the highest speed t raax ap, which is achieved at the moments of the system passing through the equilibrium position.
The maximum kinetic energy WK of a photoelectron is determined from the Einstein equation: hv - А WK; WK Av - A.
Scheme of installation for observation of the photoelectric effect. But the maximum kinetic energy of each electron emitted from the metal does not depend on the intensity of illumination, but changes only when the frequency of the light incident on the metal changes. So, when illuminated with red or orange light, sodium does not show a photoelectric effect and begins to emit electrons only at a wavelength less than 590 nm (yellow light); in lithium, the photoelectric effect is found at even shorter wavelengths, starting from 516 nm (green light); and the ejection of electrons from platinum under the action of visible light does not occur at all and begins only when platinum is irradiated with ultraviolet rays.

But the maximum kinetic energy of each electron emitted from the metal does not depend on the intensity of illumination, but changes only when the frequency of the light incident on the metal changes.
Find the maximum kinetic energy of the a-particles resulting from the exothermic reaction Oie (d - a) N14, the energy of which is Q 3 1 MeV, if it is known that the energy of the bombarding deuterons is Ea 2 MeV.
Determine the maximum kinetic energy of neutrons Wmax arising in the reaction t d - n iHe under the action of tritium t, which itself is obtained by the absorption of slow neutrons in 6Li according to the reaction n 6Li - - t - f - oc.
Fermi is the maximum kinetic energy KOj that an electron can have at absolute zero.
Therefore, the maximum kinetic energy of a neutron emitted by beryllium is 7 8 106 electron volts, which corresponds to a velocity of about 3 9 109 cm sec. Since the mass of the neutron must be almost equal to the mass of the proton, it is natural to assume that the maximum velocities of both particles must be almost the same. The highest observed velocity for a proton is 3 3 109 cm sec., a similar value for a neutron is consistent with Chadwick's views on the origin of the neutron.
What is the maximum kinetic energy of free electrons at OK in copper.
What is the maximum kinetic energy of an individual nucleon if the nucleus of the atom is at the lowest energy level.
The atom has maximum kinetic energy at the position at the midpoint, which corresponds to top speed his movements. But since in this position the speed of the atom is maximum, the time it spends in this state is minimal. However, most of the collisions between molecules occur precisely in these phases of the vibration, and a much smaller part in the phase in which the conditions for the transfer of energy of the vibration are most favorable.
Here Gmais is the maximum kinetic energy.
The table shows the maximum kinetic energy that can be transferred to each atom by an electron with a threshold energy.
The second law of the photoelectric effect: the maximum kinetic energy of photoelectrons increases linearly with the frequency of light and does not depend on the intensity of light - J ta.
At a constant light intensity, the maximum kinetic energy of the ejected electrons is characterized by a simple linear dependence on the light frequency. Moreover, such a linear relationship has the same slope for all materials under study; thus, this slope is a characteristic of the photons themselves. Thus, we have found the connection that we were looking for: the connection between the wave characteristics of a beam of light and the only characteristic energy that the photons of this beam carry.
The retarding voltage U3 depends on the maximum kinetic energy that the electrons ejected by the light have.
The numerator of the logarithm argument 2m0V2 represents the maximum kinetic energy that a light particle can receive in a head-on collision with a - particle.
This relationship is shown in Fig. 4.62. The maximum kinetic energy of photoelectrons increases linearly with the frequency of the incident light and does not depend on its intensity. The measurements showed that for each metal there is a cutoff frequency or wavelength of the incident light at which the energy of the photoelectron is zero; at this and lower frequency (or greater wavelength) light of any intensity does not cause a photoelectric effect. This frequency (wavelength) is called the red border of the photoelectric effect.

On fig. 286 shows a graph of the dependence of the maximum kinetic energy E t of electrons emitted from the surface of barium during the photoelectric effect on the frequency v of the irradiating light.
On fig. 11.6 shows the results of measuring the maximum kinetic energy of photoelectrons as a function of the frequency of light irradiating the metal for aluminum, zinc and nickel.
filling quantum states electrons in a metal.| Plot of the distribution function for a degenerate gas of fermioids at an absolute value. From fig. 3.6 shows that the maximum kinetic energy will have an electron located at the Fermi level. This energy is measured from the bottom of the pit and is always positive.
But at large numbers electrons, their maximum kinetic energy is large, and, consequently, the de Broglie wavelength is small. Therefore, the condition for the applicability of the proposed method is that the number of electrons in an atom be large enough compared to unity.
Lukirsky and S. S. Prilezhaev experimentally confirmed linear dependence the maximum kinetic energy of photoelectrons on the frequency of the incident light.
By measuring the blocking potential pr, one can determine the maximum kinetic energy (and velocity) of the electrons leaving the cathode.
By measuring the blocking potential fg, one can determine the maximum kinetic energy (and velocity) of the electrons leaving the cathode.
Of all compared devices, the conoidal nozzle is characterized by the maximum kinetic energy of the jet.
Installation diagram for study.| The dependence of the photocurrent on the voltage. These measurements made it possible to establish the second external photoelectric law: the maximum kinetic energy of electrons knocked out by radiation does not depend on the intensity of radiation, but is determined only by its frequency (or wavelength X) and the material of the electrode.
Show that, with the strength of the flywheel material unchanged, the maximum kinetic energy depends only on the volume, but not on the mass of the flywheel.