Science project, Physical/mechanical learning, teacher's Demo props on the class, birthday for friends, families, parents etc. Demonstrate the structure and working principle of the electric bell, which can be observed directly or through optical projection. The electric bell model is made of metal and wood base, precisely casted, the parts are all polished by professional abrasives. During the experiment, if the vibrating piece works abnormally, the distance between the screw and the point of the vibrating piece can be adjusted. Use a wire to connect the two terminal posts to a 4-6v DC power supply, and install a