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1986年我在给学生讲授《交流电》时,考虑到交流电的大小和方向随时间而变化,其图像是正弦曲线这一点比较抽象,学生不好理解和记忆。就设计了这样一个实验:将大号(没有大号的小号也可以)马蹄形磁铁靠近发光的白炽电灯泡,这时可以明显看到灯丝强烈振动。磁铁移开,灯丝振动消失。这个实验强烈地激发了学生的好奇心,引起了他们的思考。灯丝发生振动的原因是:1.通电导线在磁场中受安培力的作用;2.磁铁周围的磁场恒定,若灯丝中通过的是稳恒电流,则灯丝所受安培力恒定;3.由于灯丝中通过的是大小和方向都随时间而变化的交流电,则其所受安培力亦随时间而变(包括大小和方向)。4.故灯丝发生振动,而且是一种周期性的受迫振动。所以交流电的大小和方向的随时间而变化也是周期性的。
When I was teaching students “AC Power” in 1986, taking into account that the size and direction of AC power changed over time, the image was sinusoidal, which was more abstract, and students did not understand and remember it. An experiment was designed to place a large (without large trumpet) fine horseshoe-shaped magnet close to a glowing incandescent bulb, where the filaments can be seen to vibrate strongly. As the magnet moves away, the filament disappears. This experiment strongly inspired students’ curiosity and caused them to think. The reasons for the vibration of the filament are as follows: 1. The energized wire is affected by the amperage force in the magnetic field; 2. The magnetic field around the magnet is constant; if the filament passes a steady current, the amperometric force of the filament is constant; 3. Since the filament In the case of alternating currents that change in size and direction over time, the amperage they experience also changes over time (including size and direction). 4. The filament is vibrated and it is a periodic forced vibration. Therefore, changes in the size and direction of AC power over time are also cyclical.