演示实验在物理教学中有着非常重要的意义。它可以激发学生学习物理乃至其他自然科学的热情，培养学生的观察能力，加深对所学知识的理解。在电磁学教学中，常常需要演示某一电路中有无电流，电流方向如何。通常的做法是：在电路中接一电流计或白炽灯泡，观察电流计的指针是否 Demonstration experiment has very important significance in physics teaching. It can stimulate students’ enthusiasm for studying physics and even other natural sciences, develop students’ observation abilities, and deepen their understanding of what they have learned. In electromagnetism teaching, it is often necessary to demonstrate whether there is a current in a certain circuit and how the current direction is. The usual practice is: to connect a galvanometer or incandescent bulb in the circuit, observe whether the current meter pointer is