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Dec 1957

Volume 25, Issue 9, pp. 591-651

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Conversion of Solar to Electrical Energy

G. L. Pearson

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 591

Online Publication Date: Jul 2005

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A photovoltaic device has been developed which converts solar radiation directly into electrical energy with an over-all efficiency of 11%. This consists of a p-n junction formed by gaseous diffusion near the front surface of a silicon plate. In full sunlight a single cell furnishes approximately 30 ma of short circuit current per square centimeter of surface, 0.6 v of open circuit voltage, and 12 mw of power into a matched load per square centimeter of surface. Like other electric batteries, individual cells may be connected in series or parallel to obtain an increase in terminal voltage or current. The spectral response is a maximum near 0.7 µ, and the long wavelength cutoff is at approximately 1.1 µ. The efficiency of this new silicon p-n junction photovoltaic cell is greater by a factor of 20 than that previously reported for other types of photocells and makes the conversion of the sun's energy directly into electricity possible for a number of interesting applications. A Bell System field trial at Americus, Georgia, in which solar batteries are used to power a rural carrier telephone communication system, is described. A number of other possible applications for this new solar energy converter are discussed.

Theory for Simple Machines

Harald C. Jensen

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 599

Online Publication Date: Jul 2005

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A theory is presented for a simple machine that gives a relationship between the efficiency and the load lifted by the machine. The theory is shown to be valid for data taken from a pulley system.

Analysis of the Social Consequences of Scientific Discovery

Richard L. Meier

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 602

Online Publication Date: Jul 2005

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Present formulations of the responsibility of scientists for the social consequences of their efforts are not very helpful for the stabilization of society. More accurate estimates of the impact of a set of new developments can be generated if administrative scientists assigned a small group of specialists to the task while the ground-breaking research was still under way. An efficient procedure for such a group would be to (1) achieve an understanding of the scientific foundations of the impending innovation, (2) select those “futures” for the society for consideration which offer interesting changes in structure, and (3) develop ad hoc models for these futures into which the innovation may be introduced and exert changes. By such means a first approximation of the effects can be deduced. A more refined picture can be obtained by considering the relevant public decisions which have to be made, the convergence of the path of this innovation with others, and hypothetically “looking back” from some point in the future and describing the successive stages of the impact. These techniques are aimed at minimizing the surprise afforded at decision-making levels by developments in science.

Notes on Jumping

Paul Kirkpatrick

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 614

Online Publication Date: Jul 2005

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Sutton's conclusion about the forces on the human tibia is shown to be invalid but correct. There is no rational basis for the fairly common impression that broad jumpers should take off at 45°. Subject to simplifying assumptions about the mechanism of the broad jumper it is shown that athletes in this event should take off at less than full speed. The leg motions of broad jumpers in air serve a useful purpose. The application of physics and other sciences to the techniques of sport is a neglected but promising enterprise.

Galvanometer Resistance and Linearity

Bernard L. Miller

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 617

Online Publication Date: Jul 2005

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The values of galvanometer resistance which are obtained by the two half-deflection methods (constant-voltage versus constant-current sources) are often found to differ because of nonlinearity in the galvanometer response. It is shown that the correct value is the geometric mean of the results of the two methods, if the initial deflections are the same in the two cases; also, the galvanometer resistance equals that value of the variable resistance in the two methods which gives the same second deflection. A new method which resembles the Kelvin method of obtaining the resistance of a galvanometer is reported. The source of the nonlinearity is apparently in the torsional response of the galvanometer coil suspension and not in a lack of uniformity in the magnetic field through which the coil turns.

Determination of the Velocity of Light from Electromagnetic Measurements According to W. Weber and R. Kohlrausch

F. Kirchner

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 623

Online Publication Date: Jul 2005

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In 1856 a paper by W. Weber and R. Kohlrausch was published in Poggendorf's Annalen (Vol. 99, p. 10) under the title: “The Quantity of Electricity which flows in Galvanic Currents through the Cross-Section of a Conductor.” This paper represents a short abstract of a detailed paper by the same authors which appeared in the same year 1856 in the Abhandlungen der Koeniglich Saechsischen Gesellschaft der Wissenschaften, in Leipzig as “Electrodynamic Measurements Particularly Basing Current Intensity Measurements on Mechanical Measurements.” The results of these measurements, which the two authors report in these papers, became of such fundamental importance for the further development of physics that a commemoration of this pioneering work, which in the last decades has been given little attention, seems desirable.

David Alter on the Light of the Electric Spark

E. C. Watson

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 630

Online Publication Date: Jul 2005

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The one hundred and fiftieth anniversary of the birth of the American physician and physicist, David Alter, occurs this year. It is proposed to celebrate this anniversary by reproducing his two pioneer papers in spectrum analysis published in 1854 and 1855 in the American Journal of Science.

Experiment on the Reflection and Absorption of Neutrons

R. J. Stephenson and T. F. Samsel

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 632

Online Publication Date: Jul 2005

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Fast neutrons from a radium-beryllium source were slowed down in paraffin and detected by a boron-trifluoride proportional counter. The absorption of the neutrons in aluminum and their reflection by paraffin blocks were measured using electronic amplifying and counting equipment.

Pinhole-Camera Experiment for the Introductory Physics Course

Albert V. Baez

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 636

Online Publication Date: Jul 2005

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The pinhole-camera experiment serves as an introduction to geometrical and physical optics as well as the theory and practice of photographic processing. Factors affecting exposure, density, and resolution may be studied experimentally with this inexpensive piece of equipment.

Demonstration of Gravitational Attraction with the Cavendish Balance

Hans Meissner

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 639

Online Publication Date: Jul 2005

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A Cavendish balance is described, which has a period of 3.5 min and gives a deflection of the light beam of 3 mm at a distance of 1 m when the position of the outer spheres is changed. This deflection is read with a pair of phototubes which, driving a cathode follower, give a current of 44 µa or more depending on the tube used for the cathode follower. The current can be read with a projection meter. The damping of the balance can be adjusted between critical damping and almost zero.

Two-Nucleon Forces and Nuclear Saturation

Robert Karplus and Kenneth M. Watson

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 641

Online Publication Date: Jul 2005

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Brueckner has adduced considerable evidence that the observed proton-proton, proton-neutron, and neutron-neutron forces lead to stable atomic nuclei whose density is independent of their size. The experimental information and the theoretical arguments that lead to this conclusion are reviewed.
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Automatic Constant Pressure Regulator for Gas Viscosity and Other Measurements

N. Fuschillo

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 648

Online Publication Date: Jul 2005

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Abstract Unavailable

Newton's Law of Cooling

G. F. Landegren

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 648

Online Publication Date: Jul 2005

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Abstract Unavailable
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Coupled Torsion Pendulums

Julius Sumner Miller

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 649

Online Publication Date: Jul 2005

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Abstract Unavailable

Empirical Gravitational Equation

Roy Weinstein

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 650

Online Publication Date: Jul 2005

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Abstract Unavailable
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Franklin and Newton—An Inquiry into Speculative Newtonian Experimental Science and Franklin's Work in Electricity as an Example Thereof. I.

Bernard Cohen, Author and Duane Roller, Reviewer

American Journal of Physics -- December 1957 -- Volume 25, Issue 9, pp. 650

Online Publication Date: Jul 2005

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Abstract Unavailable
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