50Hz是我們中國交流電的頻率，其含義是：一秒鐘之內(nèi)，交流電按照正弦波變化了50次，T1~T3是一個完整的周期，時長為：1秒除以50等于0.02秒，T1~T2，T2~T3都是0.01秒，這表示一個周期內(nèi)電流有兩次瞬間為零，但燈泡為什么沒有出現(xiàn)閃爍呢？主要原因有兩個：其一，閃爍速度太快，人眼難以察覺；其二，燈泡靠加熱燈絲發(fā)光，電流瞬間過零時燈絲無法完全冷卻，光會減弱但看上去依然是連貫的。

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.