# What is Alternating current: Definition and 121 Discussions

Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa. In certain applications, like guitar amplifiers, different waveforms are used, such as triangular waves or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information such as sound (audio) or images (video) sometimes carried by modulation of an AC carrier signal. These currents typically alternate at higher frequencies than those used in power transmission.

View More On Wikipedia.org
1. ### B How can scalars like voltage, impedance, etc. be added like vectors?

So we learnt about the different types of circuits and their behaviour when connected to an alternating current source. (DC was treated as an AC with 0 frequency and/or infinte time period). For purely inductive and purely capacitive circuits we were shown the derivation and why things are the...
2. ### I Alternating current in a perfect conductor

Premise: the electric field inside a perfect conductor is zero. The boundary conditions indicate that the tangential component is continuous, so the tangential component at the surface of the conductor is also zero. In conclusion, the electric field is perpendicular at the surface of a perfect...
3. ### Engineering Calculating maximum flux density

Hi everyone, I have a EE problem that I need to sort out for alternating voltage. I have to find out the maximum flux density. B_max= integral from 150 degrees to 30 degrees (u/(2NA) dt is my problem. I have a hard time to integrate this since I am to integrate with time and not degrees or...
4. ### B Resonance state - Alternating current

In alternating current, is the resonance state that the phase angle of the current is 0?
5. ### B Formulas for the alternating current and voltage

Hi,I have found in my textbook the formulas for both current and voltage and I have no idea if they are right or wrong. Can someone help me with these formulas? v=v0cos(wt) i=i0cos(wt) Is this correct? In google when I search for the answers I get something else: v=v0sin(wt) i=i0sin(wt)
6. ### Engineering Alternating current circuit with transformer

Hi, I don't understand how to solve the problem below for (a). First I transform the cirucuit to direct current problem using jw method. Now i see that U=-I2Z. Z=R2+Zc3=R2+1/jwC3=4,5+1/[j(1000)(10^-3*0,25)]. Then I use impedance transformation to get rid of the transformator(using Z0), but then...
7. ### Engineering Transfer function of AC Transformer

I'm solving this exercise, first I did a force diagram for the transformer nucleus and I got this: ∑Fx = ma P(t) - Fk - Fb = ma P(t) = mx''+ bx' + kx So I got that dynamic equation, my question is, after transform that dynamic equation to Laplace Domain how can I relate it with the Output...
8. ### Alternating current and Average power

For a current i(t)=I_0\sin(\omega t+\varphi_0) period is ##T=\frac{2\pi}{\omega}##, Power is defined as p(t)=Ri^2(t). So period of power is not any more ##T=\frac{2\pi}{\omega}##. Why then average power is P=\frac{1}{T}\int^T_0p(t)d t. Why are we using the period of current and not of the...
9. ### How can I find the DC component of an Output Sinusoidal Voltage?

I had previously solved this using Root Mean Square method by integrating the value of voltage from t=0 to t=T/2 and then from t=T/2 to t=T.Answer was Vo/2½.Yesterday I found this question👇🏾 if I followed the previous approach then: 5 volts is not even in the option. How can I find the DC...
10. ### Why do you need a line 2 on an Alternating Current circuit?

Preface to thread: The power source in both diagram 1 and diagram 2 is a wall outlet with alternating current power, not a battery. The load in both diagram 1 and diagram 2 is a light bulb, even though I forgot to label the load in diagram 2...
11. ### Boundary conditions for a purely inductive load in an AC circuit

Hi all, Kirchhoff's equation for this simple circuit is equivalent to \dot I=\frac{V}{L} Where V=V_0 \sin(\omega t). Integrating both sides should give I(t) = -\frac{V_0}{L\omega} \cos(\omega t)+c where c is an arbitrary constant (current). Here, most of the derivations I've found simply drop...
12. ### Determine the effective current value in the circuit with C and R

Given: U = 220 V f = 50 Hz r = 20 Ohm C = 100 μF Find: I Solution: 1) Xc = 1/(ω*C) = 1/(2*π*f*C) = 1/(2*π*50*10^-4) = 31.83 Ohm 2) R_eq - equivalent resistance R_eq = (r*Xc)/(r+Xc) = (20*31.83)/(20+31.83) = 12.28 Ohm 3) I = U/R_eq = 220/12.28 = 17.9 A True answer given in the textbook is 13 A...
13. ### How to calculate the voltage induced in a coil by an AC magnetic field?

So, as it says in the title, I am trying to calculate overall voltage induced in a coreless coil in the cases of it being stationary and moving in an alternating magnetic field. To go more into detail, I would like to create a mathematical model of a coil in an alternating magnetic field that...
14. ### What will the phasor diagram of this LCR circuit looks like?

I know the current of capacitor and inductor must be parallel but pointing in opposite direction due to the fact they are connected in parallel thus having same voltage (please see attached screenshots). The current of resistor will simply be the sum of these two vectors, but what about its...
15. ### 𝑗 - 𝜔 method alternating current circuit help

I'm supposed to calculate the current and the phase angle. Can someone please tell me if this is the correct solution?
16. ### How to solve a complex equation to get the current?

I was reading The Feynman Lectures on physics http://www.feynmanlectures.caltech.edu/I_23.html chapter 23, section 4. In it he derives the equation for current when inductor, resistor and capacitor is connected in series with an alternating voltage source, he derives this equation:-...
17. ### I Phase differences in Transformers

How is the phase difference between the current in the primary coil and induced e.m.f. in the secondary coil be 90*??
18. ### Relation between power factor and phase angle

Homework Statement apparently your effective power is V_maxI_max * cos(x) where x is the phase angle. So I must consider only real power Homework Equations power = VI current = I sin(wt) The Attempt at a Solution Let impedence be = e^ix . I'll write current as Ie^i(wt) consideronly the real...
19. ### Hall Effect in an alternating current circuit

Since the classical Hall EMF is proportional to current, in an alternating current circuit, the Hall Emf should also follow an alternating pattern. Is it so? Or the Hall Emf doesn't change in a sine wave pattern instead remains more or less same and has a voltage based on the average/rms...
20. I

### Calculating capacitance from an AC circuit

This question is from my physics book and neither I nor my teacher can find the mistake in my method. (The original question is not in English so I'll do my best translating it) > When a coffee maker is connected to the wall (230 V, 50 Hz) its power consumption is 180 W. The power consumption...
21. ### Neutral wire in electric power distribution between substations

I had learned from a book in a lower class that electric power distribution from the generating station is done in phases. Like in India, we have three phases of power transmission: the red, green and yellow colours distinguish the three phases. I believe the same is the case in any other...
22. ### Understanding the Flow of Electrons in AC Circuits

In DC, we have learned that the electrons move from their position through the conductor, resulting in a current. They leave their positions on the application of a potential difference, and move or flow in the direction of higher to lower potential, thereby causing a current. But what about...
23. ### Electric field of AC source

Hello everybody I got really confused. I want to calculate the Electric-Field of an alternating current source( Sine(wt)). I do not know what is its equation. I need to run it in Matlab to get a result. Can you please give me some hints? I need to write the equation to calculate the E-field in...
24. ### Problem regarding periodic current functions

Homework Statement Three periodic currents have the same ##f=100 Hz##. The amplitude of the second current is ##4 A##. and is equal to half of the amplitude of the third current. Effective value of the third current is 5 times that of the first current. At time ##t_1=2ms## third current...
25. ### Help understanding phasor solution

Homework Statement From the given circuit and provided information draw a phasor and calculate the inductance. Homework Equations 3. The Attempt at a Solution [/B] The paper was given to me at class as a solution to our homework and i can't understand how they drew the phasor and drew the...
26. ### AC Current in GHz Frequency and Zero Resistance

Hello Experts, I am a physics newbie with big ideas. I have a question. I am thinking about how to produce a zero Resistance Current. We know we can do this using super-conductors in sub zero temperature, but maybe there's another way. My assumptions (which could be wrong): 1) Resistance in a...
27. ### Alternating Current, live and neutral wires

Hi there, I am a teacher and will be teaching the topic of alternating current soon. I have not taught this before and have certainly not studied this in many years so I am trying to get a full understanding and am looking for a bit of clarification. So I know that the current supplied by the...
28. ### Inductive charging: Emf induced in two coil loops

Homework Statement So I'm trying to figure out this problem: The base of our charging station is composed of a coil with N1 turns and area A1 connected to a 120 VAC, 60 Hz source. The device has a smaller coil with N2 turns and area A2, which when attached will fit completely inside the...
29. ### Why does the value of u change with the orientation of the loop?

Homework Statement https://goo.gl/wifHB3 {Image from: Electricity - Basic Navy Training Courses; NAVPERS 10622} http://imgur.com/a/Pm2Rl Here are two images, the one with colours is from my textbook. I don't understand why u is 0 when the thing inside is parallel with the ground and why...
30. ### Classical Searching for an Advanced Textbook on Alternating Current

As the title implies, I'm looking for a textbook on alternating current (not necessarily containing only about this topic). I'm looking for such a book with the following things in mind: - Is not just some introductory thing, but a book that treats the subject in an advanced manner using at...
31. ### Does AC form a closed loop circuit?

Some say that AC should form a closed loop circuit for electricity utilization but is there really an loop from the Power station(hot wire) to the Ground(neutral) and then from Ground to power station so that it forms a loop?
32. ### How do Capacitors and Inductors Add/Remove VARS in AC?

To my understanding, capacitors cause the current to lead the voltage which adds VARS to the circuit and inductors cause the current to lag behind the voltage which removes VARS (in AC circuits). Also, it is my understanding that VARS increase voltage. I work for one of the largest utilities...
33. ### Can Alternating Current Sources Stabilize Z-Pinch Fusion?

Hey everyone, I've been kicking around this idea for fusion for a while and thought everyone could check my understanding. The idea is to create a sustained z pinch using alternating current sources in parallel...
34. ### Alternating current peak value

Homework Statement If the peak values of current through inductor (L), capacitor (C) and resistor (R) in parallel AC circuit are 2mA, 3mA, and 5mA respectively, then the peak value of current delivered by the source in the same circuit will be Homework EquationsThe Attempt at a Solution i (R)...
35. ### AC Generator With Repelling Magnets

Hi Everyone, I have 4 scenarios in question . Will The EMF(Voltage) be the same in all of the scenarios? - the difference between the two photos are the polls: one repel one attract . - i understand that the current(amps) will change due to the wire length assuming same gauge 1) Photo...
36. ### Varying Direct Current and Alternating current

Homework Statement I've been struggling to fully understand the difference between Varying Direct Current and Alternating Current. Please explain this to me. Also, how would they differ on a Current-Time graph? Homework Equations E = int (VI dt) The Attempt at a Solution
37. ### Power Factor of an L-C-R curcuit

Homework Statement A series L-C-R circuit Comprises of a 250mH coil, 0.01 MFD capacitor and a 5W resistor. A dependent voltage defined by e = 2.5cos(80000t) is applied across it. Determine the power factor. [/B] Homework Equations Power Factor = cos(x) = R/Z Z = sqrt^[R^2 + (XL - XC)^2] The...
38. ### Calculating Active Effect & Effect Factor for Alternating Current

Homework Statement An inductor has a resistance of 30 Ohm and an inductance of 0,1 H. A current with the peak value of 2 A runs through. Calculate the effect factor and the active effect if it connects to a grid with 230V and a frequency of 50 Hz. My book says that the effect factor is 0,69...
39. ### Magnetic levitation using alternating current

Hi, I have a few questions regarding magnetic levitation achieved by using alternating current to induce eddy current on a non-ferromagnetic conductor plate to provide the levitation force. 1. Can it be stabilized? If yes, in what ways? 2. Are there any equations/formulae or ways to calculate...
40. ### Single-Phase to Three-Phase Cycloconverter

When my classmate report about cycloconverters. He discussed about different classifications and types of cycloconverters. He also discussed how Single-phase to Single-Phase Cycloconverters operate. But when he approached Three-Phase to Single-Phase and Three-Phase to Three-Phase...
41. ### Follow-up question about my understanding on rectification

I understand the process of rectification but just only in theory. But I still have questions that I guess will be answered if I can experience or has experience about it (but sadly I don't have). Please kindly answer these questions: 1. Does the waveform of Vout can be considered as DC (...
42. ### How is sinusoidal current generated?

I'm delving into AC as well as attempting to understand the various wave forms used in electrical engineering, and I am curious how engineers are able to generate current which alternates in a sinusoidal manner. What specific phenomena allows us to achieve this? Is it a special circuit, or does...
43. ### Understanding Analog Signals & AC

Also can we have an analog signal in alternating current?
44. ### RC Circuit with alternating voltage source

Homework Statement I'm supposed to find the current in a circuit with a voltage source, capacitor, and resistor in series. The voltage source is described by V=V0ejwt. Here, j is the complex number j2=-1, and i is the current Homework Equations I=C*dv/dt The Attempt at a Solution I have...
45. ### Question about Alternating Current

I'm a bit confused on some of the fundamentals of Alternating Current, if anyone could help me out it would be awesome. 1) In what form is the mechanical energy provided to an alternator to produce the electrical energy? Does someone sit at each generator and spin a hand-crank (joke)? 2)...
46. ### Electrical grounding and alternating current

When households are said to be grounded using an Earth wire, electrons are supposed to flow to the ground because the ground is at zero volts. For example, if your the live wire touches the metal casing of your toaster then the Earth wire takes the current to ground. But isn't a lot of household...
47. ### Engineering RCL circuit alternating current, calculate current sum

Homework Statement Consider, in the circuit from the image, i1(t) = 5 cos(2t + 10º) v1(t) = 10 cos(2t - 60º). Find the value of the current ix(t). Options given: A: ix(t) = 9.9 cos(2t - 129.2º) B: ix(t) = 9 cos(2t - 29.2º) C: ix(t) = 99 cos(2t + 129.2º) D: ix(t) = 0.99 cos(2t +...
48. ### Alternating current, voltage, sinusoids

Homework Statement Consider v1 = 30 sin(ωt + 10º) and v2 = 20 cos(ωt - 40º) A: v1 is in advance to v2 B: v1 differs 50º from v2 C: v2 is in advance to v1 D: v1 is in quadrature to v2 Homework Equations The Attempt at a Solution I think the correct answer is A because v1's angle is nearer...
49. ### The half-wave rectification of an alternating current

Homework Statement Explain the use of a single diode for the half-wave rectification of an alternating current. The Attempt at a Solution A rectifier is a device that converts an alternating current, which periodically changes polarity, to direct current, which flows in only one...
50. ### Want to know how alternating current really works

All I have read in the electricity class is that AC is any type of current which actually reverses its directions periodically. I have also read all sorts of mathematical expressions concerning sine-wave form of AC. I have also understood how AC generator works. These topics had never bothered...