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. Rings with even 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 deg 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.
The construction and use of a simple apparatus to measure the magnetization density and magnetic susceptibility of ferromagnetic, paramagnetic, and the diamagnetic solids and liquids are described. The apparatus is valuable in demonstrations, student laboratories, and undergraduate research.
The transformations between the normal and metastable state of EL2 in GaAs are investigated. We apply the internal friction technique as a probe for very small conductivities and discuss the changes in conductivity by the formation and recovery of EL2*. At 40 K both shallow acceptors and EL2 are photoquenched into neutral metastable states. The acceptors are likely to be associated with EL2* forming an electrically inactive state. We identify two damping peaks at 60 and 95 K with the regeneration of the acceptors and EL2 respectively. The latter indicates a regeneration via the charged defect (EL2)+
The internal friction technique is applied to investigate the transformations between the normal and metastable states of EL2‐like defects in undeformed and deformed GaAs. By deformation EL2‐like defects are introduced, which are quenchable by light. A spatial distribution of the transformation rate is found which is discussed in terms of stress variations throughout the sample. The recovery of metastable EL2* and a metastable EL2*‐acceptor complex can be observed in undeformed material by the emission of carriers but not in deformed material. The latter result is attributed to dislocation levels, which act as traps for the released carriers.
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