Establishement of the magnetic flux density standard in the range 100 µT to 1000 µT
The magnetic flux density standard in the range 100 µT to 1000 µT has been established using a standard Helmholtz coil. The ambient magnetic field including earth's magnetic field components inside the room and other noises has been compensated to a level of the order of 100 nT. A circular triaxial Helmholtz coil pair of size nearly 800 mm has been used for compensating the ambient magnetic field. The standard Helmholtz coil of size 300 mm has been placed in the geometrical centre of the triaxial Helmholtz coil pair. The magnetic flux density has been measured using triaxial and single axis fluxgate magnetometers. The coil constant of the standard Helmholtz coil has been found to be 850.6808 ± 0.0036804 µT/A, which is in good agreement with the manufacture's specification viz, 850 µT/A, with an uncertainty of < ± 0.5 %.
Traceable magnetic measurements.
Abstract The practical realization of traceability in magnetic measurements is reviewed with particular reference to magnetic sensors, instrument calibration and methods of measurement of soft magnetic materials under both ac and dc magnetization conditions.
Influence of electric fields on friction electrification between metals and borosilicate glass
Abstract In a cylindrical geometry, electric fields were applied through the entire contact area between the sliding metal and the glass surface. The maximum electric charges developed on the metal were measured and plotted against the applied voltage producing the field. The metals were high-purity nickel and gold. The borosilicate glass was Pyrex, brand 7740. The experiments with nickel, which has a work function greater than that of the glass, were performed in 10 −7 mm Hg vacuum. The experiments with gold, with a work function smaller than that of glass, were carried out in air at atmospheric pressure. The results show that: 1. 1) There is both asymmetry and a reversed slope portion in the charge vs. voltage plot. 2. 2) For a certain range of reversing fields, the electric charge developed on the nickel is always negative and the charge on gold is always positive.