![]() We can now look back at the electromagnetic spectrum above and realize that it is also ordered by energy gamma photons each carry more energy than ultraviolet photons and so on down the line. The formula for luminous intensity (I v) is defined using the concept of radiant intensity (I e) and the luminous efficacy (K m) of the emitted light. During the light reactions, ATP and NADPH are generated by two electron-transport chains, water is used and oxygen is produced. However, this would mean, that two electromagnetic waves of the same amplitude but with different frequencies would have the same intensity, which shouldnt be the case as the higher frequency wave carries more energy. These particles, we call them photons, each carry a certain amount of energy, namely \ The energy of a photon, \(E\), is equal to Planck's constant, \(h\), (a number Max Planck found in his explanation of blackbody radiation, another of those minor issues physics was dealing with back then, and one we'll be seeing a lot of in this course) times the frequency, \(\nu\). Under the light-dependent reactions, the light energy is converted to ATP and NADPH, which are used in the second phase of photosynthesis. According to the formula given, the intensity of light is completely independent of the frequency. While the wave picture of light is good for many things, sometimes, like when trying to understand the photoelectric effect, it is more useful to think of light as being made of particles. Indeed there is a characteristic threshold frequency for each metal below which there are no electrons ejected regardless of the intensity of the incident light (well, until you throw in so much energy you turn the metal into a plasma, but that is cheating, that is not the photoelectric effect).Īlbert Einstein won the Nobel Prize in Physics (1921) in part for his explanation of the photoelectric effect. If the wavelength is too large (the frequency too low) for the particular metal, no electrons will be ejected at all. These two molecular properties determine the wavenumber at which a molecule will absorb infrared light. Here, the reduced mass refers to (M 1 M 2)/(M 1 +M 2) where M 1 and M 2 are the masses of the two atoms, respectively. Play around with the photoelectric effect simulation available at PhET you should find that while the number of electrons ejected depends on the intensity of the light, the energy of those electrons depends on the wavelength of the light. Only two variables in equation(4) are a chemical bonds force constant and reduced mass. One of those issues was the photoelectric effect, in which light striking a metal surface ejects electrons from the metal. While the above picture of light is all well and good, there were a few outstanding "issues" in physics at the end of the 19 th and beginning of the 20 th century. Light is made of particles called photons where c is the speed of light, 2.998 x 10 8 m/s. Rate laws or rate equations are mathematical expressions that describe the relationship between the rate of a chemical reaction and the concentration of its reactants. Because a hydrogen atom with its one electron in this orbit has the lowest possible energy, this is the ground state (the most stable arrangement of electrons for an element or a compound) for a hydrogen atom.\) The relation between the wavelength (Greek lambda) and frequency of a wave (Greek nu) is determined by the propagation velocity v, such that. As described in the previous module, the rate of a reaction is affected by the concentrations of reactants. at a lower potential energy) when they are near each other than when they are far apart. \) indicates that the electron-nucleus pair is more tightly bound (i.e.
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