There is a threshold frequency below which no electrons are ejected, because the individual photon interacting with an individual electron has insufficient energy to break it away.
Einstein gave the first successful explanation of such data by proposing the idea of photons—quanta of EM radiation. It is a far more general concept than its explanation of the photoelectric effect might imply. All EM radiation can also be modeled in the form of photons, and the characteristics of EM radiation are entirely consistent with this fact. As we will see in the next section, many aspects of EM radiation, such as the hazards of ultraviolet UV radiation, can be explained only by photon properties.
More famous for modern relativity, Einstein planted an important seed for quantum mechanics in , the same year he published his first paper on special relativity. His explanation of the photoelectric effect was the basis for the Nobel Prize awarded to him in Although his other contributions to theoretical physics were also noted in that award, special and general relativity were not fully recognized in spite of having been partially verified by experiment by Although hero-worshipped, this great man never received Nobel recognition for his most famous work—relativity.
What is the maximum kinetic energy of electrons ejected from calcium by nm violet light, given that the binding energy or work function of electrons for calcium metal is 2. The energy of this nm photon of violet light is a tiny fraction of a joule, and so it is no wonder that a single photon would be difficult for us to sense directly—humans are more attuned to energies on the order of joules.
But looking at the energy in electron volts, we can see that this photon has enough energy to affect atoms and molecules. A DNA molecule can be broken with about 1 eV of energy, for example, and typical atomic and molecular energies are on the order of eV, so that the UV photon in this example could have biological effects. The ejected electron called a photoelectron has a rather low energy, and it would not travel far, except in a vacuum.
The electron would be stopped by a retarding potential of but 0. In fact, if the photon wavelength were longer and its energy less than 2. This simply means that the nm photons with their 2. You can show for yourself that the threshold wavelength is nm blue light. This means that if calcium metal is used in a light meter, the meter will be insensitive to wavelengths longer than those of blue light. Such a light meter would be completely insensitive to red light, for example.
See how light knocks electrons off a metal target, and recreate the experiment that spawned the field of quantum mechanics. Skip to main content. Introduction to Quantum Physics. Search for:. The Photoelectric Effect Learning Objectives By the end of this section, you will be able to: Describe a typical photoelectric-effect experiment.
Determine the maximum kinetic energy of photoelectrons ejected by photons of one energy or wavelength, when given the maximum kinetic energy of photoelectrons for a different photon energy or wavelength. Einstein's idea that light consists of bundles of energy, photons, makes sense for explaining the photoelectric effect. Here is what he concluded. The maximum energy of an emitted electron is equal to the energy of a photon for frequency f i.
This says that it takes only one photon to eject an electron, so the intensity of photons or the intensity of light is not the key factor if the energy of not one of the photons is great enough. For an electron to be ejected from the surface of a metal, sufficient energy must be applied to break its bond with the atom from which it originates You can get a good description of the photoelectric effect from the Colorado's Physics Website.
Planck's formula explained the thermal spectrum of solid objects. Bohr's picture of the atom explained the discrete energies colors seen when hydrogen gas is heated. It also explained in less exact detail, but in a qualitatively correct way the spectra observed for other atoms.
Bohr's picture of the atom begins with the Rutherford model of a minature planetary system obeying classical mechanics, where electrons are like planets executing circular orbits around the nucleus. Bohr adds three key postulates to the Rutherford model. The Bohr picture explains the emission and absorption spectra of hydrogen, and hydrogen-like atoms superbly well. In this case mass is not conserved and the mass of an object is not the sum of the masses of its parts.
Thus, the mass of a box of light is more than the mass of the box and the sum of the masses of the photons the latter being zero. Relativistic mass is equivalent to energy, which is why relativistic mass is not a commonly used term nowadays. In the modern view "mass" is not equivalent to energy; mass is just that part of the energy of a body which is not kinetic energy. Mass is independent of velocity whereas energy is not.
Let's try to phrase this another way. You can interpret it to mean that energy is the same thing as mass except for a conversion factor equal to the square of the speed of light. Then wherever there is mass there is energy and wherever there is energy there is mass. In that case photons have mass, but we call it relativistic mass. Another way to use Einstein's equation would be to keep mass and energy as separate and use it as an equation which applies when mass is converted to energy or energy is converted to mass--usually in nuclear reactions.
The mass is then independent of velocity and is closer to the old Newtonian concept. In that case, only the total of energy and mass would be conserved, but it seems better to try to keep the conservation of energy.
Is equal to HF? What are the units of E in E HF? Who proposed E HF? Can you use E HF for electrons? What does HF stand for in physics? What is E hv called? What is the definition of a photon?
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