scholarly journals Some Photo-electric Properties of the Alkali Metals. III. The Dependence of Photo-Electric Current on the Wave-Length of the Incident Light

1910 ◽  
Vol 30 (3) ◽  
pp. 385-393
Author(s):  
F. K. Richtmyer
Keyword(s):  
Electric Current ◽  
Alkali Metals ◽  
Incident Light ◽  
Wave Length ◽  
Electric Properties

The continuous absorption of light in alkali-metal vapours

1953 ◽  
Vol 219 (1136) ◽  
pp. 89-101 ◽  
Keyword(s):  
Cross Section ◽  
Alkali Metals ◽  
Theoretical Calculations ◽  
Wave Length ◽  
Energy Difference ◽  
Continuous Absorption ◽  
Absorption Of Light ◽  
Sodium Vapour ◽  
Good Agreement ◽  
Dipole Length

The first section of this paper is an account of some experiments on the absorption of light in sodium vapour from the series limit at 2412 Å to about 1600 Å (an energy difference of 2·6 eV). The absorption cross-section at the limit is 11·6 ± 1·2 x 10 -20 cm 2 . The cross-section decreases giving a minimum of 1·3 ± 0·6 x 10 -20 cm 2 at 1900 Å and then increases to 1600 Å. A theoretical calculation by Seaton based on the dipole-length formula gives good agreement with the experiments at the series limit and also correctly predicts the wave-length for the minimum, but it predicts a significantly lower absorption at the minimum. The experiments described in the first section of the paper conclude a series on the absorption of light in the alkali metals. The second section consists of a general discussion of the results of these experiments and of their relation to theoretical calculations. There is good agreement between theory and experiment except in regard to the magnitude of the absorption at the minimum.

scholarly journals The molecular scattering of light in vapours and in liquids and its relation to the opalescence observed in the critical state

1922 ◽  
Vol 102 (715) ◽  
pp. 151-161 ◽  
Keyword(s):  
Critical Point ◽  
Critical State ◽  
Incident Light ◽  
Wave Length ◽  
Molecular Scattering ◽  
Avogadro’S Number ◽  
Quantitative Manner ◽  
The Mean ◽  
Good Agreement ◽  
Molecular Scattering Of Light

It has long been known that in the immediate vicinity of the critical state, many substances exhibit a strong and characteristic opalescence. In recent years, the phenomenon has been studied by Travers and Usher in the case of carefully purified CS 2 , SO 2 , and ether, by S. Young, by F. B. Young in the case of ether, and in a quantitative manner by Kammerlingh Onnes and Keesom in the case of ethylene. An explanation of the phenomenon on thermodynamic principles as due to the accidental deviations of density arising in the substance was put forward by Smoluchowski. He obtained an expression for the mean fluctuation of density in terms of the compressibility of the substance, and later, Einstein applied Maxwell’s equations of the electromagnetic field to obtain an expression for the intensity of the light scattered in consequence of such deviations of density. He showed that the fraction α of the incident energy scattered in the substance per unit volume is 8 π 3 /27 RT β ( μ 2 – 1) 2 ( μ 2 + 2) 2 /N λ 4 (1) In this, R and N are the gas constant and Avogadro’s number per grammolecule, β is the isothermal compressibility of the substance, μ is the refractive index and λ is the wave-length of the incident light. Keesom tested this formula over a range of 2·35° above the critical point of ethylene and found good agreement except very close to the critical point.

scholarly journals The photoelectric effect for γ-rays

1931 ◽  
Vol 133 (822) ◽  
pp. 381-406 ◽  
Keyword(s):  
Atomic Number ◽  
Incident Light ◽  
Wave Length ◽  
Incident Radiation ◽  
Photoelectric Effect ◽  
Short Wave ◽  
Matrix Elements ◽  
Rest Energy ◽  
Large Wave ◽  
Heavy Atoms

1. Introduction .—A discussion of the photoelectric effect for hydrogen­ like atoms has been given by many authors. In the simplest case it is assumed that the wave-length of the incident radiation is large compared with the “ radius of the atom.” If z be a co-ordinate measured from the centre of the atom, the axes may be chosen so that the perturbing vector potential involves the factor exp. (±2π i z /λ), where λ is the wave-length of the radiation. For very large wave-lengths we put this equal to unity, or we may use the first two terms of the expansion. For very short wave-lengths, however, the expansion is illusory, and we must use some other method. For γ-ravs the “radius of the atom” is large compared with the wave-length of the rays. A knowledge of the wave-function near the nucleus is therefore necessary. Further, the photo-electrons emitted have velocities comparable to that of light. In view of these two circumstances it is necessary to use a relativistic theory of the atom, and in the following we shall endeavour to apply the theory of the Dirac electron. In 2 we develop a normalised solution of the equations for the hydrogen­like atom, when the total energy, E, is greater than mc 2 , the rest energy of an electron. Next we consider the perturbation theory, which gives the total number of electrons emitted and their resultant forward momentum, in terms of the matrix elements representing transitions from the ground state to states where the electron is free. The chief difficulty is the evaluation of these matrix elements, which is only carried through when the atomic number Z is small, and the wave-length of the incident light is such that the energy of one quantum is comparable to mc 2 , corresponding to wave-lengths of the order 10 -10 cm. The first restriction is very unsatisfactory, since the photoelectric effect is best observed in heavy atoms. The results obtained are, however, in qualita­tive agreement with the experimental results for heavy atoms, if we exclude the variation with atomic number.

Determination of microvascular oxyhemoglobin saturations using cryospectrophotometry

1990 ◽  
Vol 259 (6) ◽  
pp. H1912-H1920 ◽  
Author(s):  
B. M. Fenton ◽  
T. E. Gayeski
Keyword(s):  
Optical Density ◽  
Incident Light ◽  
Wave Length ◽  
Empirical Relationship ◽  
Complex Function ◽  
Vessel Diameter ◽  
Experimental Measurements ◽  
Independent Calibration ◽  
Hb Concentration

Although a four-wavelength method for cryospectrophotometric measurement of intravascular oxyhemoglobin (HbO2) saturations has previously been described, the relationship between experimental measurements and theory has not been clearly detailed. The current work utilizes an empirical relationship between HbO2 saturation measurements and reflected light oximetry, which is consistent with the two-flux theory of Kubelka and Munk (Z. Tech. Phys. 11a: 593-603, 1931). To obtain linear, concentration-independent calibration curves, the theoretical results require that 1) the complex function relating optical density, scattering, and absorption can be linearly approximated over the range of scattering and absorption coefficients used; and 2) the scattering coefficient is independent of wavelength. Incident light cannot easily be measured using reflection spectroscopy, which precludes the determination of isosbestic points. Therefore, equibestic wave-length pairs were used at which optical density differences were invariant with saturation. This allows numerous wavelength sets over the range 540-600 nm to be selected, rather than the limited choices of isosbestic wavelengths. Finally, the effects of freeze rate, freeze depth, Hb concentration, and vessel diameter are each discussed in terms of their influence on experimental measurements.

scholarly journals VII. On the emission velocities of photo-electrons

1913 ◽  
Vol 212 (484-496) ◽  
pp. 205-226 ◽  
Keyword(s):  
Experimental Evidence ◽  
Incident Light ◽  
Wave Length ◽  
Ultra Violet ◽  
Metallic Surfaces ◽  
Quantitative Evidence ◽  
Maximum Emission ◽  
Violet Light ◽  
Decisive Test ◽  
Electric Effect

Since the discovery of the photo-electric effect by Hertz, many experiments have been made on the emission of negative electricity from metallic surfaces when illuminated by light. Yet with regard to many important points the results are often indefinite and contradictory. Most theories of the photo-electric effect indicate definite relations between the velocity of emission of the electrons and ( a ) the nature of the metal from which they are emitted, and ( b ) the wave-length of the incident light. Up to the present, however, the experimental evidence as to these two relations must be regarded as quite inadequate to afford any decisive test between rival theories. This research was undertaken to obtain, among other things, quantitative evidence on these two relations. 2. Previous Work .— Ladenburg made some valuable experiments on the velocity with which electrons are emitted from metals when illuminated by ultra-violet light. He concluded that the maximum emission velocity was inversely proportional to the wave-length. The velocity varied from metal to metal; thus, for light of wave­ length λ 2010, the maximum emission velocity (measured in volts) for platinum was 1·86 volts, and for zinc 1·12 volts. The source of light used by Ladenburg was a mercury arc. His metals were polished with emery and oil, and were exposed to the atmosphere for some time before the apparatus for measuring the velocity could be exhausted.

scholarly journals XI. Double refraction and dispersion in Iceland Spar: an experimental investigation, with a comparison with Huyghen’s construction for the extraordinary wave

1880 ◽  
Vol 171 ◽  
pp. 421-449
Keyword(s):  
Royal Society ◽  
Theoretical Calculations ◽  
Incident Light ◽  
Wave Length ◽  
Extraordinary Wave ◽  
British Association ◽  
Angle Of Incidence ◽  
Double Refraction ◽  
Light Passing ◽  
Iceland Spar

In a paper read before the Royal Society, June 20, 1878, the results of an investigation into the truth of Fresnel’s theory of double refraction in a biaxal crystal were stated. The comparison between theory and experiment was made by a method suggested by Professor Stokes (British Association Report, 1862), according to which the reciprocal of the velocity of wave propagation was determined by experiment and also on Fresnel’s theory. The greatest difference between the two amounted to ·0009, and there appeared to be some connexion between the differences and the wave length of the light used. In the endeavour to follow up this connexion I undertook a series of similar experiments with light of different wave lengths, using three lines of the hydrogen spectrum and the sodium line. The extreme smallness of the arragonite prisms I had previously worked with led me to use, at first at least, Iceland spar, which could be obtained in large pieces with ease, and for which the theoretical calculations were greatly more simple. Professor Stokes had already made a series of experiments by the same method with this substance (Proceedings of the Royal Society, vol. 20, p. 443) and arrived at results confirming Huyghen’s construction. The details of his experiments are as yet unpublished, and I venture to think it might be useful to have arranged in tabular form a series of results, to serve in the future as a test of any theory of double refraction which might be proposed. The method of the experiments, as suggested by Professor Stokes (British Association Report, 1862), is as follows: A prism is cut from a piece of spar, and the position of its faces with reference to the cleavage faces carefully determined. The prism is mounted on a spectrometer, and the collimator adjusted so that the rays of a definite wave length falling on the prism are parallel, the edge of the prism being parallel to the axis of revolution of the reading telescope. The deviation of the light passing through the prism in any position is observed, also the position of the image of the slit formed by reflexion at the face of incidence. From this and the known direction of the incident light we can calculate the angle of incidence. Let this be Ф . Let the deviation be D and the angle of the prism i . Let V be velocity of the light in air, v in the crystal. Let ψ be the angle of emergence, Ф′ ψ′ the angles which the wave normal in the crystal makes with the faces of the prism.

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