摘要:

We calculate the magnetic induction from the integral form of the Biot-Savart law,B = μ0/4π∫(J+Ḋ) × rdV/r3. In the quasistatic case, using only the scalar electric potential, we transform the volume integral ofḊinto an inner and an outer surface integral, both of which vanish except for a contribution from the polarization current in dielectric materials. Hence the induction is calculable from the sum of the conduction- and polarization-current densities alone. This result has no bearing on the calculation of the induction from Ampere's law, where we must use the entire displacement-current density. In the converse problem of an induced electric field there is no magnetic conduction current, and the quasistatic magnetic displacement current arises from a changing electric current in a closed circuit. We expressHthrough the scalar magnetic potential, which is discontinuous on a surface bounded by the electric circuit. We obtain the induced electric field from a volume integral like the Biot-Savart integral above, and as before we transform it into surface integrals. There are two nonvanishing contributions. One is over both sides of the surface which is bounded by the electric circuit; it gives an expression for the electric field which we commonly compute from the vector potential. The second contribution reappears as a volume integral of magnetization currents in magnetic material.

ISSN:0002-9505    

DOI:10.1119/1.1971712

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

摘要:

A wave-packet formalism is presented for obtaining the differential cross section for the elastic scattering of a single particle by a potential. The method avoids difficulties inherent in the more common formulations such as interference between incident and scattered waves, box normalization, and density of final states. The time sequence of events in the scattering process is pictured in an intuitively appealing manner. The initial form of the wave packet is specified explicitly, and the time development of the wave packet is determined from the time-translation operator. The asymptotic form of the wave packet is investigated after a sufficiently long time lapse, and the cross section is obtained from a calculation of particle flux densities.

ISSN:0002-9505    

DOI:10.1119/1.1971718

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

摘要:

Several demonstrations or experiments illustrating the coherence properties of laser light are described. In addition, a summary is given of demonstrations in interference and diffraction which make use of the high intensity of a laser source. These are discussed specifically within the capabilities of a 0.1-mW laser, the size that is most likely to be available for teaching in an average physics department.

ISSN:0002-9505    

DOI:10.1119/1.1971721

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

摘要:

A simple experiment to measure the reverberation time of a room is described. The relevant theory is outlined, and typical results are given. The experiment is designed for inclusion in a course of practical work for first-year university students in physics.

ISSN:0002-9505    

DOI:10.1119/1.1971726

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

摘要:

A student experiment is outlined using a multichannel pulse-height analyzer, in multiscaler mode of operation, to make repeated observations of statistically distributed events. Experiments on the distribution of repeated counting observations, the distribution of intervals between (successive and scaled) events, and binomial distributions are described. In this way, hundreds of observations can be made and recorded in a short time; and the student may devote his laboratory period to the analysis of his own experimental data. One laboratory session provides time enough to investigate several sets of real experimental data, and thus experiments become practical which might not otherwise be considered.

ISSN:0002-9505    

DOI:10.1119/1.1971731

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

摘要:

A simple apparatus using microwaves for demonstrating the Doppler frequency shift resulting from reflection of a wave train from a moving mirror is described.

ISSN:0002-9505    

DOI:10.1119/1.1971736

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

摘要:

The motion of spheres under the combined effect of gravity and aV2drag force is considered. It is shown that for conditions such as are described by Galileo inDialogues Concerning Two New Sciences, one should expect a difference upon reaching the ground of several feet in height between a 1-lb sphere and a 100-lb sphere.

ISSN:0002-9505    

DOI:10.1119/1.1971740

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.1971745

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.1971750

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.1971761

出版商:American Association of Physics Teachers    

年代:1965

数据来源: AIP