How much kinetic energy will photoelectrons produced possess? (b) Suppose this metal is illuminated with light having a wavelength λ = 225 nm. That leads to production of a current upon illumination of the metal due to ejected electronsĬalculate the energy per photon associated with light of this frequency. That was obtained in the first example above.įor a certain metal, the threshold frequency ν 0, or minimum frequency of EM radiation The conversion to kJ/mol involves using Avogadro's number and converting J to kJ:Įxercise: Calculate these same quantities using the value of ν for 535 nm radiation Thus the energy carried by a single photon of 535 nm light is Using the relation E = hc/λ (and converting nm to m), we obtain E = (6.626 × 10 −34 J (which will be sufficiently precise for the number of significant figures of the calculation input): Solution: We'll use truncated values of the following constants Useful for converting between EM wavelength and energy.Įxample: How much energy (J) is carried by one photon ofĪfter finding the energy of one photon of each wavelength,Įxpress the energy of a mole of these photons in kJ/mol. Wavelength, and wave speed with the Planck-Einstein relation above, we obtainĪn alternate form of the Planck-Einstein relation, If we combine the equation relating frequency, The factor h is known as Planck's constantĪn important fundamental constant of nature. Of EM radiation of a given frequency ν is given by the following key equation (often called the In other words, EM radiation has aįurthermore, Einstein showed that the energy E, of each of these small bundles, or quanta, (in the nano- and picoscale realms of atoms and subatomic particles)Įlectromagnetic radiation and the quantum nature of energy and matterĪlthough classical physics had explained most of its behavior as a result of its waveīehaves as if its energy is carried at the atomic scale in small bundles of energy Ultimately, we learn that EM radiation manifests both wave and particle properties, while matter To account for certain observations such as black body radiation and theĪ quite different model is provided quantum theory, which postulates a Thus we also discuss the nature of light and theĬuriously, although light and other forms of EM radiation can be well described as energyĪs shown by the phenomenon of interference, the wave description fails in its ability The most revealing phenomena concern the interplay between light and atoms, We continue our investigation of the nature of atoms by first considering someįundamental aspects of energy and energy changes. Since most of the secrets of modern atomic theory have been revealed throughĬareful investigation of the interactions between matter and
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