50Hz是我们中国交流电的频率，其含义是：一秒钟之内，交流电按照正弦波变化了50次，T1~T3是一个完整的周期，时长为：1秒除以50等于0.02秒，T1~T2，T2~T3都是0.01秒，这表示一个周期内电流有两次瞬间为零，但灯泡为什么没有出现闪烁呢？主要原因有两个：其一，闪烁速度太快，人眼难以察觉；其二，灯泡靠加热灯丝发光，电流瞬间过零时灯丝无法完全冷却，光会减弱但看上去依然是连贯的。

How to understand 50Hz alternating current?

50Hz is the frequency of alternating current in China, and its meaning is: within one second, the alternating current changes 50 times according to the sine wave. T1 to T3 constitutes one complete cycle with a duration of 1 second divided by 50, equaling 0.02 seconds. Both T1 to T2 and T2 to T3 are 0.01 seconds. This means that the current is instantaneously zero twice in one cycle, but why doesn't the light bulb flicker? There are two main reasons:first, the flickering speed is too fast for the human eye to detect; second, the light bulb emits light by heating the filament, and when the current is instantaneously zero, the filament cannot cool down completely, so the light will dim but still appear continuous.