What are the important knowledge points of alternating current?

Alternating currentKnowledge points and formula sharing:

Instantaneous value formula for sinusoidal alternating current:

e=emsinωt=nbsωsinωt

u=umsinωt

i=imsinωt

The formula for the RMS value of alternating current.

The above are all valid values and only apply to sinusoidal alternating currents).

Cycle (t) is the time it takes for an alternating current to complete a periodic change.

t=2π/ω

Frequency (f) is the number of times the alternating current completes the change of the traveling period in 1s.

f=1/t=ω/2π

Effect of capacitance and inductance on alternating current.

Capacitive Reactance Formula: Sensible Reactance Formula:

Summary of the formula of the transformer part.

Formula for the voltage relationship between the primary and secondary coils:

u1：u2=n1:n2

Formula for the current relationship between the primary and secondary coils:

i1：i2=n2：n1

Power Relationship Formula:

p1 = p2, i.e. u1i1 = u2i2

1.Voltage instantaneous value e=emsin t, current instantaneous value i=imsin t; （ω2πf）

2.Peak electromotive force em = nbs = 2blv peak current (pure resistive circuit.

Middle) im = em r total.

3.The effective value of sine (co)sinusoidal alternating current: e=em (2)1 2;u=um/（2）1/2；i=im/（2）1/2

4.The relationship between voltage and current and power in the primary and secondary coils of an ideal transformer.

u1/u2=n1/n2；i1/i2=n2/n2；p in = p out.

5.In long-distance transmission, the use of high-voltage transmission of electric energy can reduce the loss of electric energy on the transmission line =(p u)2r; (P loss: power lost on the transmission line, P: total power of the power transmitted, U: transmission voltage, R: resistance of the transmission line);

6.The formula is a physical quantity.

and Unit: angular frequency.

rad/s）；t: time(s); n: number of coil turns; b: magnetic inductance (t); s: area of the coil (m2); uOutput) voltage (v); i: Current intensity.

a）；P: Power (W).

Note: (1) The frequency of alternating current is the same as the frequency of rotation of the coil in the generator, i.e.: electricity = line, f electricity = f line;

2) In the generator, the magnetic flux of the coil at the neutral position.

maximum, induced electromotive force.

If the zero god is scattered, the direction of the current over the neutral plane will change;

3) The RMS value is defined according to the thermal effect of the current, and the AC value of the rock servant is not specifically stated to refer to the RMS;

4) When the turns ratio of the ideal transformer is constant, the output voltage is determined by the input voltage, the input current is determined by the output current, and the input power is equal to the output power.

When the power consumed by the load increases, the input power also increases, that is, p out determines p in;

Image The effect of resistance, inductance, and capacitance on alternating currents.

Description of alternating current: An electric current that periodically changes in magnitude and direction over time.

In electromagnetism, the amount of electricity passing through any cross-section of a conductor per unit time is called electric current, and the current symbol is i, and the unit is ampere (a), which is referred to as "ampere".

André Marie Ampère (1775 1836), French physicist and chemist, was distinguished by his research on electromagnetism, as well as his contributions to mathematics and physics. The SI unit of electric current is named after its surname).

The free charge in the conductor moves regularly and directionally under the action of the electric field force to form an electric current.

Electrically stipulated: the direction of the directional flow of positive charge is the direction of the current. In addition, in the project, the directional flow direction of the positive charge is also the current direction, and the magnitude of the current is expressed by the charge Q flowing through the conductor section per unit time, which is called the current intensity.

Heating. When the conductor is energized, it generates heat, and this phenomenon is called the galvanic thermal effect. For example, Joule's law, which is more familiar, is a law that quantitatively states that conduction current converts electrical energy into thermal energy.

Magnetic effect. The magnetic effect of electric current: Oster discovered that any wire that is connected with an electric current can produce a magnetic field around it, which is called the magnetic effect of electric current.

Chemical effects. The chemical effect of electricity is mainly due to the chemical change of matter due to the participation of charged particles (electrons or ions) in the electric current. Water electrolysis or electroplating in chemistry are chemical effects of electric current.

Alternating current is an alternating current, an electric current that changes periodically in magnitude and direction over time. Direct current is the opposite. Power grid companies generally use alternating current to transmit electricity, but there are high-voltage direct current for long-distance high-power transmission, submarine cable transmission, and communication between asynchronous AC systems.

Compared with the high-voltage AC transmission mode, the HVDC transmission mode has obvious advantages Historically, it was only due to technical reasons that AC transmission replaced DC transmission The following is a comparison of the main advantages and disadvantages of AC and BC DC, so as to illustrate their respective value in application

The advantages of alternating current are mainly manifested in power generation and distribution: the use of alternators based on the principle of electromagnetic induction can be very economical and convenient to convert mechanical energy (water rotten silver flow energy, wind energy......Chemical energy (oil, gas......and other forms of energy converted into electrical energy; Compared with DC power supplies and DC converter stations of the same power, the cost of AC power supply and AC substation is much lower; Alternating current can be easily boosted and stepped down through the transformer, which brings great convenience to the distribution of electrical energy This is the unique advantage of alternating current compared with direct current

The alternator has a simple structure, and it is relatively easy to change the voltage level with a transformer, and it is widely used. The structure of DC generators is complex, the cost is high, and the voltage change also needs to pass through electronic equipment such as thyristors, which is also expensive, and the basic power grid is not so widely used.

Ten. 4. Alternating current (sinusoidal alternating current).

1.Voltage instantaneous value e=emsin t, current instantaneous value i=imsin t; (ω2πf)

2.Peak electromotive force em nbs 2blv current peak (in pure resistive circuit) im em r total.

3.The effective value of sine (co)sinusoidal alternating current: e=em (2)1 2;u＝um/(2)1/2 ；i＝im/(2)1/2

4.The relationship between voltage and current and power in the primary and secondary coils of an ideal transformer.

u1/u2＝n1/n2； i1/i2＝n2/n2；p in = p out.

5.In long-distance transmission, the use of high-voltage transmission of electric energy can reduce the loss of electric energy on the transmission line 0 7 (p u)2r; (p loss 0 7: power lost on the transmission line, p:.)

The total power of the transmitted electrical energy, U: the transmission voltage, R: the resistance of the transmission line) See Book II, P198;

6.Equation Quantities and Units: Angular Frequency (rad s); t: time(s); n: number of coil turns; b: magnetic inductance (t);

s: area of the coil (m2); uOutput) voltage (v); i: current intensity (a); P: Power (W).

The main knowledge points of alternating current.

First of all, we must know the expression of the alternating current, its image (sine or cosine image), the neutral plane starts to rotate with sinusoid, and the parallel magnetic inductance lines start to rotate corresponding to the cosine diagram. Secondly, there are three quantities: instantaneous value (for capacitance breakdown, withstand voltage, etc.), average value (for electric power), and effective value (for heat effect, power, etc.). Then there is the resistance of resistors, inductance coils, and capacitors to the circuit, and then there is the structure, type, use, and calculation of the transformer.

Finally, there is the delivery of electrical energy. That's all for the college entrance examination knowledge points.

Alternating current, abbreviated as AC, refers to an electric current that changes periodically in both magnitude and direction, because the average operating value of the periodic current in a cycle is zero, which is called alternating current or simply alternating current.

Usually the waveform is sinusoidal. Alternating current can transmit electricity efficiently. But there are actually other waveforms that are used, such as triangular waves, square waves. The mains power used in daily life is alternating current with a sinusoidal waveform.

Direct current refers to the current that does not change its direction and magnitude periodically. Also known as constant current.

Alternating current, alternating current is also known as "alternating current", referred to as "alternating current". Generally refers to the voltage or current that periodically changes in size and direction over time. Note.

Refers to cyclical changes.

PS: Absolutely original. Hope. Thank you.

Direct current, that is, only in one direction, such as river water, but the flow may vary in size, drought and rain, etc.

A constant current, like water in a water pipe, is directed in a wise direction and the flow rate remains the same.

Alternating current, alternating current is also known as "alternating current search", referred to as "alternating current". Generally, the size and direction of the anterior leakage finger change periodically over time.

Among them, the simplest AC is called sinusoidal alternating current.