- #1
McQueen
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Suppose that you are an observer in a room equipped with only one window measuring 1 m sq. The window is glazed with a glass pane 1 cm. Thick. The only source of illumination is a green surface outside the window. Hence the only light entering the room is the green light from this surface. Taking the following:-
1) Speed of light through glass = 2.5 x [tex]10^{5}[/tex]km/sec
2) diameter of atom = [tex]10^{-10}[/tex]m
3) thickness of glass = 3 mm.
Then we find that the light passes through the glass in approx. 1.2 x [tex]10^{-11}[/tex] secs. and that the time taken for a single photon to be absorbed and re-emitted by an electron as it passes through the glass in the process known as photon conduction is an incredible 4 x [tex]10^{-19}[/tex]secs.
Having demonstrated the incredible speed with which a photon of light is absorbed and re-emitted by the electrons of the atoms belonging to the substance it is passing through , the glass pane in the window has served its purpose and can be removed. We turn next to the green surface outside the window whose reflected light illumines the interior of the room and examine the process by which this takes place. Making, for the moment , the assumption that the origin of the reflected light is an intense source of white light , we come to the following conclusions:- Some frequencies of the white light are absorbed by the atoms of the green surface , but are not re-emitted , their energies being absorbed instead by recoiling against the nucleus , this raises the energy of the atom resulting in the emission of heat , other frequencies of the white light find no corresponding energies in the electrons present in the atoms of the green surface and pass through the substance without any interactions taking place , lastly the energies and wave lengths corresponding to green light (i.e., those of 550Nm and an energy of 2.2 eV) are absorbed and re-emitted by the electrons of the atoms of the green surface at the rate of 5.4 x [tex]10^{14}[/tex]Hz/sec}. We now deal with the question of the manner in which the electrons emit these photons , do they emit these photons at random in the manner of a spinning Catherine wheel or do they emit the photons in a single line? The manner in which photons are absorbed and emitted as they pass through a substance like glass would seem to indicate that the latter is true , however we will not draw any conclusions from this at present but depend on further observations to inform our views. To do this we must re-enter the room and join the observer. Let us assume that the observer is equipped with a particularly sensitive densiometer with which he can measure the intensity of the light coming through the window. At first he stands at a distance of 1m. from the window and notes down the intensity. He then shifts back from the window to a distance of 2m and again measures the intensity of the light , he finds that the intensity of the light is now 1/4 that of the intensity he had recorded at a distance of 1m from the window. He keeps repeating the readings at varying distances until he comes to the conclusion that the intensity of the light varies inversely with the square of the distance from the window and also that the area over which the light spreads varies directly with the square of the distance from the window. ( In actual fact of course the window is large and diffraction would make such a measurement difficult , remember this is an experiment.) He repeats his readings under identical circumstances over the course of several days and always gets the same results. What conclusions does he draw from his observations ? Firstly he notes that the intensity of the light varies inversely with the square of the distance from the window and secondly he notes that the area over which the light spreads varies directly with the square of the distance from the window. He concludes that originally the light was more intense because more photons were being absorbed per atom (i.e a number of photons were giving up their energy in succession) and also that due to the interaction of the light with the air or with some medium in the air , the number of photons being absorbed by each individual atom has been reduced and that this reduction has taken place uniformly , in other words the photons which originally were arranged in a single line had spread out into a number of lines while at the same time maintaining a uniform intensity (i.e., each of the new lines has an equal number of photons.) Thus it would seem that the intensity of light is not due to the energy of the photon alone but to its energy x frequency and that the number of photons due to this frequency varies inversely with the square of the distance from the source.. Thus at the source the intensity would be 2.2 x 5.4 x [tex] 10^{14}[/tex] = 1.18 x [tex]10^ {14}[/tex]eV per sec. or roughly 1 x [tex]10^{-5}[/tex] watts per atom per sec. And so on. Notice that if the duration is reduced the intensity is also reduced , thus the amount of energy reaching an electron in the destination point in [tex] 10^{4}[/tex] secs would be 2.2eV . Further it must be assumed that as each electron absorbs a photon it immediately re-emits it at the same frequency.
Also light emitted by a photon bound to an atom will always obey the inverse square law because it is a point source while light from lasers also obey the inverse square law but since they are being emitted by a comparatively massive source of free electrons , travel longer in a coherent beam. At a distance of 1,609m , a helium-neon laser (which is a well collimated source ) will spread out over an area of 1.3m.
1) Speed of light through glass = 2.5 x [tex]10^{5}[/tex]km/sec
2) diameter of atom = [tex]10^{-10}[/tex]m
3) thickness of glass = 3 mm.
Then we find that the light passes through the glass in approx. 1.2 x [tex]10^{-11}[/tex] secs. and that the time taken for a single photon to be absorbed and re-emitted by an electron as it passes through the glass in the process known as photon conduction is an incredible 4 x [tex]10^{-19}[/tex]secs.
Having demonstrated the incredible speed with which a photon of light is absorbed and re-emitted by the electrons of the atoms belonging to the substance it is passing through , the glass pane in the window has served its purpose and can be removed. We turn next to the green surface outside the window whose reflected light illumines the interior of the room and examine the process by which this takes place. Making, for the moment , the assumption that the origin of the reflected light is an intense source of white light , we come to the following conclusions:- Some frequencies of the white light are absorbed by the atoms of the green surface , but are not re-emitted , their energies being absorbed instead by recoiling against the nucleus , this raises the energy of the atom resulting in the emission of heat , other frequencies of the white light find no corresponding energies in the electrons present in the atoms of the green surface and pass through the substance without any interactions taking place , lastly the energies and wave lengths corresponding to green light (i.e., those of 550Nm and an energy of 2.2 eV) are absorbed and re-emitted by the electrons of the atoms of the green surface at the rate of 5.4 x [tex]10^{14}[/tex]Hz/sec}. We now deal with the question of the manner in which the electrons emit these photons , do they emit these photons at random in the manner of a spinning Catherine wheel or do they emit the photons in a single line? The manner in which photons are absorbed and emitted as they pass through a substance like glass would seem to indicate that the latter is true , however we will not draw any conclusions from this at present but depend on further observations to inform our views. To do this we must re-enter the room and join the observer. Let us assume that the observer is equipped with a particularly sensitive densiometer with which he can measure the intensity of the light coming through the window. At first he stands at a distance of 1m. from the window and notes down the intensity. He then shifts back from the window to a distance of 2m and again measures the intensity of the light , he finds that the intensity of the light is now 1/4 that of the intensity he had recorded at a distance of 1m from the window. He keeps repeating the readings at varying distances until he comes to the conclusion that the intensity of the light varies inversely with the square of the distance from the window and also that the area over which the light spreads varies directly with the square of the distance from the window. ( In actual fact of course the window is large and diffraction would make such a measurement difficult , remember this is an experiment.) He repeats his readings under identical circumstances over the course of several days and always gets the same results. What conclusions does he draw from his observations ? Firstly he notes that the intensity of the light varies inversely with the square of the distance from the window and secondly he notes that the area over which the light spreads varies directly with the square of the distance from the window. He concludes that originally the light was more intense because more photons were being absorbed per atom (i.e a number of photons were giving up their energy in succession) and also that due to the interaction of the light with the air or with some medium in the air , the number of photons being absorbed by each individual atom has been reduced and that this reduction has taken place uniformly , in other words the photons which originally were arranged in a single line had spread out into a number of lines while at the same time maintaining a uniform intensity (i.e., each of the new lines has an equal number of photons.) Thus it would seem that the intensity of light is not due to the energy of the photon alone but to its energy x frequency and that the number of photons due to this frequency varies inversely with the square of the distance from the source.. Thus at the source the intensity would be 2.2 x 5.4 x [tex] 10^{14}[/tex] = 1.18 x [tex]10^ {14}[/tex]eV per sec. or roughly 1 x [tex]10^{-5}[/tex] watts per atom per sec. And so on. Notice that if the duration is reduced the intensity is also reduced , thus the amount of energy reaching an electron in the destination point in [tex] 10^{4}[/tex] secs would be 2.2eV . Further it must be assumed that as each electron absorbs a photon it immediately re-emits it at the same frequency.
Also light emitted by a photon bound to an atom will always obey the inverse square law because it is a point source while light from lasers also obey the inverse square law but since they are being emitted by a comparatively massive source of free electrons , travel longer in a coherent beam. At a distance of 1,609m , a helium-neon laser (which is a well collimated source ) will spread out over an area of 1.3m.
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