How to define the effective current in ac - knoweasy

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How to define the effective current in ac

July 12, 2021

Alternating current (ac) for people on the vast global village is not strange, its biggest advantage is that can realize long-distance uhv transmission circuit. Alternating current (ac) is called alternating current (ac), because it's the direction of the current and size as the change of time and change of its functionCurrent value of I= lmaxsinwt, among them for the first time

Imax is the peak value of the alternating current, w is the angular velocity of the alternating current rotating in the magnetic field, and wt is the radian of the alternating current rotating in the magnetic field. If t is one cycle of the alternating current changing, then wt is equal to 2n (assuming that the initial phase of the alternating current is 0), then the instantaneous current value of the alternating current at this time is 0.

If the resistance of the circuit is purely resistive, can be deduced from this, the ac voltage is in accordance with the number of sine change rule, namely e = UmaxSinwt, if the ac voltage and current of the multiplication, get power, namely the instantaneous power of the alternating current (ac) P = PmaxSin²wt. Although already pull on the voltage and power, let's get back now or the alternating current (ac) effective current question!

Effective current in ac popular said is refers to the rated current of ac. About its definition, is not only interesting, even ridiculous.Effective current of ac is defined, into a metal conductor is connected to alternating current (ac), after a time t, measure the conductor on the caloric value, and then restored at room temperature, the metal conductor farther on the metal conductor is connected with direct current (dc), if in the same time, the direct current (dc) on the metal conductor heat is equal to the heat generated in the ac in the same time Amount, then the effective value of the dc current is the alternating current (ac).

If use this method to measure the actual current of ac, then may put people dead. , however, they really do that, first of all, the effective value must be smaller than the peak value of alternating current (ac), and then after countless times of measurement, it eventually found that the effective current value is 1 / V2 ac peak times.

1 - Imax/V2, therefore, the effective value of ac, the effective voltage alternating current (ac) is equal to its peak value of 1 / V2, U = Umaxv2, about ac voltage value effectively, it is a misleading parameters of the capacitor, if in the design of capacitor, the effective voltage value as its breakdown voltage of the alternating current (ac), then it even on the alternating current (ac), when it is pass Into alternating current (ac), the capacitor will be breakdown.

And alternating current (ac) there is an interesting phenomenon, since we are using an alternating current is sinusoidal variation law, when an alternating current through the bulb, there will be three times in a week period of zero current through the bulb, so, why do we not see flashing light bulb?

In fact, the electric light bulb is flashing, just we can't see with the naked eye. Because of the use of alternating current (ac) in our country, its frequency is 50 hz, its change cycle is 0.025, that is to say, the household alternating current (ac) in a shine 150 times a second time, and we can to the naked eye view to the limit value is 1 second 24 times, therefore, we can't see the light bulb flickering.

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