Basics: The AC

1 - The concept of alternating current
power line is alternating currents in the afternoon and value changes over time, these changes often circulating in a certain period.

The above is the AC sine, square pulses and spikes.

Cycle and frequency of the alternating current.
The cycle of alternating current symbol interval T is the AC repeat the old location, the period is in seconds (s) 
Frequency AC : The number of times to repeat the old status of AC in a second notation is F in units of Hz

F = 1 / T

Phase AC:
Speaking of the AC phase is often said to the comparison between two alternating current has the same frequency.
* two AC phase currents are the voltage times up and down along the same:

The two AC phase

* Two phase alternating current: electric current is two times the voltage increments varied.

Two-phase alternating current

* Two reverse-phase alternating current: the two currents 180 degrees out of phase, when the current increases, the current is reduced the other and vice versa.

Two reverse-phase AC

The amplitude of the AC
amplitude of the ac voltage is the peak value of the dien.xoay way, the amplitude is higher than the voltage that is measured from the clock

Effective value of alternating current
is usually measured value from the clock and also the voltage value indicated on the power plug Zac electronic devices., 220V AC For example we are using is only effective value, the actual peak amplitude of the voltage between 220V AC 220V x 1.4 times = approximately 300V

Power of AC.
Power AC depends on the intensity, voltage and phase deviation between the two quantities above, the production is calculated by the formula:

P = UIcosα

• In which U is the voltage
• I is the current
• α is the phase angle between U and I

=> If the alternating current passes through the resistor is its middle phase of U and I are α = 0 when cosα = 1 and P = UI

=> If the alternating current passes through the coil or capacitor, then the phase difference between U and I is +90 degrees or-90do, where cosα = 0 and P = 0 (the production of alternating current passing through capacitor electric coils or a = 0)

2 - AC current passing through R, C, L

1. Alternating current passing through resistive
AC current passing through the resistor, the current and voltage in phase with each other, meaning that the maximum voltage the current increases through increased maximum return. alternating current such nature as the one-way going through or thuan.do can apply the formula of direct current to alternating current passes through resistor

I = U / R or R = U / I Ohm's law formula

P = UI formula for calculating the capacity of

2. AC pass through capacitors.
passes through alternating current, the capacitor current over voltage will soon phase 90do

AC current is earlier 
than the phase voltage by 90 degrees when passing through capacitor

* The AC pass through will be gathered together to block with an impedance called ZC, and ZC is calculated by the formula

ZC = 1 / (2 x 3.14 x F x C)

• In the ZC is the solution resistance (in units of Ohm)
• F is the frequency of alternating current (units of Hz)
• C is the capacitance of the capacitor (in units of μ Fara)

The formula shows that the resistance capacity of the capacitor is inversely proportional to frequency of alternating current (ie the higher frequencies pass through easily) and the rate nghic the capacitance of capacitor (ie capacitor with capacitance large, the AC pass through more easily)

=> The DC is the frequency F = 0 so that ZC = ∞ so that no direct current passes through the capacitor.

3. Alternating current passing through the coil.
When alternating current passes through the coil creates a magnetic field and magnetic field variation of this variable back to the main induction coil that an induced voltage in reverse, so coil which tends to resist alternating current passing through it, this resistance is the inductance of the coil denoted by Z L

Z L = 2 x 3.14 x F x L

• Where Z L is the inductance (unit is Ohm)
• L is the inductance of the coil (the unit is Henry) L depends on the number of turns winding and core materials.
• F is the frequency of alternating current (units of Hz)

From the formula above we see, the inductance of the coil proportional to the frequency and the inductance of the coil, the higher the frequency passes through the coil is more difficult => properties of the coil as opposed to convergence power.

=> With the one-dimensional, then Z L of the coil = 0 ohm, so the direct current through the coil to be only net effect of the resistance R only (or net resistance of the coil is measured by the clock Universal), if the net return of the coil is relatively small direct current through the coil will be a short circuit.

* AC power line passes through the coil, the current phase is delayed compared to the voltage 90 of voltage that is growing faster than the electric current through the coil.

AC current is slower 
than phase voltage by 90 degrees when passing through the coil

=>> Because of the phase difference between current and voltage passing through the coil and capacitor, so we can not apply Ohm's Law to AC circuits when the involvement of L and C are.

=>> Regarding export, the AC was not born when we went through L and C, although a U> 0 and I> 0.

4. Synthesis of two alternating current on the same circuit* On the same circuit, if there are two phase alternating current, the voltage amplitude will be equal to the sum of two voltage components.

Two phase current amplitude increases.

If on the same circuit, if there are two reverse-phase alternating current, the voltage amplitude is equal to the voltage signal into two parts.

Two reverse-phase currents, the amplitude decreases