From: Associate Professor John P. Ertel, Physics Department

To:     Academic Dean and Provost

Via:    (1) Director, Division of Math & Science
          (2) Chairman, Physics Department

Subj:   SABBATICAL LEAVE REPORT

The following Sabbatical Leave Information is submitted:

1. Academic rank - Associate Professor
2. Location - Code 804, DTRC
3. Dates - Fall Term, 1997
4. Work performed - See excerpts below from the preliminary FACACREC-1998 showing a list of presentations and publications resulting from this sabbatical.

1. A Classroom Jumping Ring.

Researchers: Prof. Carl S. Schneider and Assoc.Prof. John P. Ertel, Physics Department, USNA, Annapolis, MD.

Understanding the classroom jumping ring, C. S. Schneider and J. P. Ertel, Fall Meeting of the Chesapeake Section of the American Association of Physics Teachers, at the U. S. Naval Academy, Annapolis, MD, 8‚NOV‚97.

This paper focuses on the pedagogical applications of a compact but powerful apparatus to propel a conducting ring from a magnetic coil activated by household voltage. The apparatus is roughly 6x6x15 inches, containing a magnetic core and several rings which can be fired internally or externally over twenty feet at the push of a button. Physics concepts demonstrated with the apparatus include Ampere's law, Faraday's law, impedance, phase shift, magnetic pole, skin depth, temperature dependence of conductivity, Lorentz force and magnetic, kinetic and acoustic energy.

A classroom jumping ring, C. S. Schneider and J. P. Ertel, Joint Spring Meeting of the American Physics Society and the American Association of Physics Teachers, in Columbus, OH, 18‚APR‚98.

We present the design of an optimized compact alternating current jumping ring apparatus which can electromagnetically launch conducting rings across a classroom. Jump energy and height are calculated for core and thin ring length, radius, thickness and material. The effects of core saturation, permeability, hysteresis and demagnetizing field, ring shielding and convective derivative are described. Even rings with small phase lag can pass by the magnetic pole of the primary in one quarter of a cycle. Large ring size relative to skin depth delays the ring current close to the 180 degree phase lag of Lenz's law. Contactless jump height measurement enables ring resistivity determination. Demonstrating the effects of voltage, frequency, conductivity, permeability and geometry contributes to understanding electromagnetism in the classroom.

A classroom jumping ring, C. S. Schneider and J. P. Ertel, accepted for publication in the American Journal of Physics, May to July, 1998 (see attached notice).

We present the design of a compact alternating current jumping ring apparatus which can electromagnetically launch conducting rings across a classroom. Jump energy and height are calculated for core and thin ring length, radius, thickness and material. The effects of core saturation, permeability, hysteresis and demagnetizing field, ring shielding and convective derivative are described. Even rings with small phase lag can pass by the magnetic pole of the primary in one quarter of a cycle. Large ring size relative to skin depth delays the ring current close to the 180 degrees of Lenz's law. Contactless jump height measurement enables ring resistivity determination. Demonstrating the effects of voltage, frequency, conductivity, permeability and geometry contributes to understanding electromagnetism in the classroom.

Invited presentation:
Due to numerous requests from the membership and upon invitation of the Chairman of the Chesapeake Section of the American Association of Physics Teachers , we will be giving an updated presentation of last fall's basic theory and demonstrations of the Jumping Ring.

Understanding the classroom jumping ring with extensions, C. S. Schneider and J. P. Ertel, Spring Meeting of the Chesapeake Section of the American Association of Physics Teachers, at UMBC, Baltimore, MD, 2‚MAY‚98.

In this presentation, we focus on conveying an understanding of the electromagnetic jumping ring of Elihu Thomson (circa 1887). A large number of the pedagogical applications of a compact but powerful apparatus used to propel a conducting ring from a magnetic coil activated by household voltage are demonstrated. The apparatus is roughly 6x6x10 inches, including a magnetic core and several rings which can be fired over twenty feet at the push of a button. Physics concepts demonstrated with the apparatus include Ampere's law, Faraday's law, impedance, phase shift, magnetic pole, skin depth, temperature dependence of conductivity, Lorentz force and magnetic, kinetic and acoustic energy.

2. Scattering of Acoustical Power from unribbed and regularly ribbed panels.

Researchers: Assoc.Prof. John P. Ertel, Physics Department, USNA, Annapolis, MD, Joseph W. Dickey, David Taylor Research Center, Annapolis, MD, and Gideon Maidanik, David Taylor Research Center, Cardarock, MD

Mechanical and radiated power and radiation efficiency of point driven panels, J. Ertel, J. Dickey, and G. Maidanik, accepted for presentation and publication in the proceedings of the 130th Winter Meeting of the Acoustical Society of America , San Diego, CA, 1‚DEC‚97, 1aSA10.

The radiation and partial radiation efficiencies from point and line driven panels were previously defined and investigated by the authors [J. Acoust. Soc. Am. 98, 2888(A) (1995) and J. Sound Vib. 144, 71--86 (1991)]. In this paper, the mechanical power dissipated in a point driven fluid loaded panel is studied and compared to the radiated power. The interdependence of the mechanical and radiated powers is investigated, and they are related as fractions of the total input power. The dependencies of the mechanical and radiated power on frequency, fluid loading, and mechanical loss are further studied. In the present paper, the mechanical power as well as the radiation efficiency is shown to increase with increased damping in a panel while the radiated power decreases, as it must. These results again show the fallibility of the conclusion that "a higher radiation efficiency necessarily implies more radiated power.'' The results of computer experiments are cited in numerical examples.

Mechanical and radiated power and radiation efficiency of point driven unribbed and regularly ribbed panels, J. Ertel, G. Maidanik, and J. Dickey, paper targeted for late June submission in the Journal of the Acoustical Society of America.

jpe@nadn.navy.mil

Physics Department Homepage
United States Naval Academy Homepage