Mainly used to demonstrate the phenomena that occur when the inductor is powered on and off in the circuit. The phenomenon of induced electromotive force in the coil due to changes in its own current is called selfs induction. The direction of the selfs-induced electromotive force is: when the current increases, its direction is opposite to the current; when the current decreases, its direction is the same as the current direction. The demonstrator uses two inductors, a small 3.8V light bulb and a high-brightness light-emitting diode to display changes in selfs-induction phenomena. It has the characteristics of good reliability, intuitive and obvious experimental results, and easy operations. Wonderful ,sweet warm for friend family and yourself.