通电螺线管在中学物理教学中经常用到 ,学生总是把它和条形磁铁相类比。即 :螺线管通入直流电后 ,一端是Ｎ极、另一端就是Ｓ极 ;若通入交流电 ,则螺线管两端Ｎ、Ｓ极交替变化。笔者曾问过学生 ,若把小钢珠放置在通电螺线管端口 ,钢珠运动情况将如何 ?多数学生回答说钢珠停在螺 Powered solenoids are often used in middle school physics teaching, and students always compare it with bar magnets. That is, after the solenoid is connected to direct current, one end is the N pole and the other end is the S pole; if the alternating current is passed, the N and S poles of the two ends of the solenoid alternate. The author once asked the students, if the small steel ball placed in the power solenoid port, how will the ball movement? Most students replied that the ball stopped at the screw