摘要:

An electronic wave analyzer designed primarily for classroom teaching in electronics is described in detail. The analyzer is essentially a two-stage audio amplifier which contains series resonance loads tunable to frequencies between 300 and 2000 c/sec. Its purpose is to demonstrate Fourier's theorem visibly; namely, to show that any periodic voltage or current wave can be resolved into sinusoidal waves of various amplitudes and phases, whose frequencies are integral multiples of the lowest frequency present. Other electronic principles are demonstrated and a method for producing amplitude-modulated waves is shown.

ISSN:0002-9505    

DOI:10.1119/1.1933871

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

A brief survey of the need for additional physics in present-day premedical curricula is given. Since the routine courses in physics and biology usually follow the standard classical approach it is suggested that appropriate border field illustrations of the basic principles of physics in biology and medicine be introduced as a separate undergraduate course in biophysics. An outline of a successful course for junior and senior premedical students is presented.

ISSN:0002-9505    

DOI:10.1119/1.1933872

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

This small and compact power supply is set up to furnish the voltages and currents usually required in elementary experiments with electronic circuits. It is stabilized with the aid of two voltage regulator tubes. Input fuses and an output indicator lamp are installed. Wire-wound three-terminal rheostats of ample overload capacity are used to adjust output voltages. The direct-current output from any one tap is limited to about 20 milliamperes, but two or more separate currents of this magnitude may be taken simultaneously from different taps. All parts of the circuit are insulated from the chassis and cabinet; therefore any one point in the circuit may safely be grounded. Also included is an unstabilized filament supply.

ISSN:0002-9505    

DOI:10.1119/1.1933873

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

A thin-walled hollow cylinder is suspended by a fine torsion wire so that it penetrates a horizontal soap film stretched across the top of a cup. The cup is rotated at a steady speed. The film drags the cylinder around until further deflection is stopped by the torsion reaction of the wire. From the known dimensions of the cylinder and the torsion constant of the wire the drag is shown to be of the order of 0.04 dyne per cm. The measurement of the tangential drag of a soap film is suggested as an advanced undergraduate laboratory project.

ISSN:0002-9505    

DOI:10.1119/1.1933874

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

(1) Two equal thin circular rings are firmly jointed together at one point so that their planes are inclined to each other. The combination is placed on a rough horizontal plane and made to rock to-and-fro. The period is calculated and confirmed by experiment. Repetition is made with jointed disks.(2a) A right solid cone is suspended by the vertex from a fixed point on a rough vertical plane. It is made to rock through small oscillations. The period is calculated and confirmed by experiment. (2b) A right solid cone results in equilibrium on a rough plane inclined to the horizontal. It is set rocking and the period calculated and confirmed by experiment. Repetition is performed with a thin conical shell.(3) A thin circular ring is placed standing on a rough horizontal plane and leaning against a rough vertical wall. It is set rocking to-and-fro and the period calculated and confirmed by experiment. Repetition is made with leaning disks and wide bands. Variants of (3) are also performed.

ISSN:0002-9505    

DOI:10.1119/1.1933875

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

A firsthand survey was made of elementary laboratory instruction at a number of universities in Great Britain. The British type of experiments, laboratory examinations, and teaching techniques are discussed. English undergraduate laboratory education is compared with the American system. English students do many more experiments and spend in the laboratory well over twice as much time as students in America spend. The British put a great deal more emphasis on the details of technique, and carry out more experiments on viscosity, surface tension, and thermal properties than is customary in America. Certain generalizations are drawn from this study which can guide the planning of elementary courses in this country.

ISSN:0002-9505    

DOI:10.1119/1.1933876

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

Various types of composite resonators and their uses are summarized. The general equations are given for the transducer for plane ultrasonic waves, consisting of a crystal assembly with back and front plates. Applications are made to several simple cases, and expressions are tabulated for the amplitude of vibration for various combinations of half- and quarter-wave components. Consideration is given to the effect of the acoustic load on the frequency for maximal amplitude. Theoretical formulas are compared with experimental results for rods of aluminum and fused quartz excited in vibration by piezoelectric crystals.

ISSN:0002-9505    

DOI:10.1119/1.1933877

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

An experiment is described which enables the student to measure the permittivity of space and the speed of light by means of the Maxwell commutator bridge. The part of the apparatus which had to be specially constructed consists of a 1000-cps electrically driven tuning fork switch and a parallel plate capacitor without guard rings but arranged so that the edge correction could be calculated. The rest of the essential apparatus is generally on hand in the laboratory or else can be purchased at reasonable cost. The accuracy of the experiment is limited chiefly by the accuracy of the construction of the capacitor. The results obtained have given the speed of light to within 0.5 percent.

ISSN:0002-9505    

DOI:10.1119/1.1933878

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

Standard formulas for fluctuations in a grand ensemble are used (i) to obtain a new reciprocal relation between density and pressure fluctuations at critical points, including the transition temperature in a Bose-Einstein gas, (ii) to discuss the fluctuations in population of the superfluid in the Bose-Einstein theory of liquid helium, and (iii) the energy fluctuations in liquid helium and in Debye crystals. Except for a Fermi-Dirac electron gas, all relative fluctuations become infinite asT→0°K. The paper discusses briefly the significance of these results with regard to (a) the interpretation of second sound in liquid helium, and (b) the state of equilibrium near absolute zero.

ISSN:0002-9505    

DOI:10.1119/1.1933880

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP

摘要:

An account of some little-known phases of Doppler's struggling life is given at the occasion of his recent birthday anniversary. A brief analysis of Doppler's major work and its fundamental bearing upon modern astrophysics are also provided. Whether Doppler ever visited an astronomical observatory is not known. Spectroscopy and photography, which alone could prove Doppler's principle in astronomy, were still in their embryonic state during his productive years.

ISSN:0002-9505    

DOI:10.1119/1.1933881

出版商:American Association of Physics Teachers    

年代:1955

数据来源: AIP