摘要:

A simple experiment employing low cost apparatus is presented which demonstrates the falloff of intensity with distance and the transition from the near field to the far field of a line source filament incandescent light bulb. A derivation of the Poynting vector as a function of the distance away from the filament is presented which shows an exact correspondence to the derivation for the electric field from a finite line charge source in electrostatics. The experimental data of power vs distance from the filament show an inverse first power of the distance falloff in the near field, with a smooth transition to an inverse square law behavior in the far field, in good agreement with the theoretical expression when corrections for the measured angular response of the detector are included. The experiment provides an illustration of the inverse square law falloff of intensity at large distances from the source, experience with simple concepts and techniques of optical radiometry and incoherent light sources, and the analogy between incoherent light sources and electrostatics in an undergraduate laboratory. An additional short experiment provides an illustration of electrical‐to‐optical power conversion efficiency and temperature dependent resistance associated with electron–phonon scattering in metals. A derivation of isotropic, unpolarized elementary radiators from anisotropic dipole radiation is presented in the Appendix.

ISSN:0002-9505    

DOI:10.1119/1.17768

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

A good quality transmission grating in conjunction with a fixed or adjustable slit can be used to demonstrate the significant features of the intensity distribution of a grating having a variable number of slits. With this technique, the study and demonstration can be extended to a large number of slits and can also show the transition from one integral number of slits to the next.

ISSN:0002-9505    

DOI:10.1119/1.17769

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Since the arrival of high temperature superconductivity in 1987, the measurement of ac susceptibility has gradually become more popular as a large number of laboratories around the world have either already acquired an ac susceptometer or are in the process of doing so. Its advantage over other techniques is that it is an inductive, noncontact measurement that screens an entire volume of the sample. Here it is explained why this seemingly simple technique is very useful and the principle of measurement is explained in full detail. It is shown how to design and construct a low‐cost susceptometer and how to interpret the data when applied to high temperature bulk superconductors.

ISSN:0002-9505    

DOI:10.1119/1.17770

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Single crystals of CdS possess a translucent yellow color but when indium is diffused into the crystal from the vapor in an evacuated silica capsule it becomes opaque. This type of diffusion is linearly dependent on the indium concentration and produces a sharp interface between the diffused and undiffused regions of the crystal. The process of diffusion doping can be demonstrated by studying the variation of the depth of the interface with anneal time and temperature, using an optical microscope. In addition, as CdS possesses a hexagonal crystal structure of the ‘‘wurtzite’’ type, this is a sensitive method for studying diffusion anisotropy along the two principal crystal directions, and the sharpness of the interface can be demonstrated by the dispersion produced by a narrow beam of white light. This article describes how these properties can be incorporated into an undergraduate student experiment, or an open ended project for demonstrating Fick’s laws and the process of diffusion doping.

ISSN:0002-9505    

DOI:10.1119/1.18076

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

Experiments for introducing data analysis techniques in the undergraduate nuclear laboratory are presented. In particular, data from gamma spectroscopy using NaI detectors are ideal for teaching curve fitting and chi‐square analysis. An experiment well suited for error analysis is the measurement of the half‐life of a radioisotope, since the uncertainties are primarily statistical and can be determined by a well‐defined procedure. All software used in our experiments was written by students as special projects.

ISSN:0002-9505    

DOI:10.1119/1.17771

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

摘要:

A simple and inexpensive analog of the cyclotron, ideal for demonstrating the concept of the cyclotron to large classes, is presented. A metal ball, constrained by a centrally directed spring force to follow a circular path over a plane surface, is accelerated by an alternating gravitational force provided manually. A simple method of recording the orbital radius of the ball in the analog provides a sensitive method of measuring the velocity dependent rolling friction force,F=a+bv. Values ofaandbfor rough and smooth wood surfaces are found and the mechanism by which the losses associated with rolling friction arise is discussed.

ISSN:0002-9505    

DOI:10.1119/1.17772

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17773

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17774

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17775

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.17776

出版商:American Association of Physics Teachers    

年代:1995

数据来源: AIP