Demo 20-28 Hysteresis Curve

When an unmagnetized ferromagnetic material is magnetized by an external magnetic field the magnetic domains do not respond immediately and uniformly to the external field. The lag of the magnetic domains in responding to the external field is known as hysteresis. When the primary coil is activated by a 60-hertz source, the hysteresis curve of the transformer core can be demonstrated using an oscilloscope to plot a graph of the magnetic induction B of the core as a function of the impressed magnetic field H of the primary coil. Two effects can be seen, as shown in the video and in Figure 1. As H increases, B lags behind, due to hysteresis, causing the initial straight line to open up into a narrow ellipse. As the core becomes saturated, the slope of the curve decreases, as can be seen at the ends of the hysteresis curve of the Figure