What is Ac current: Definition and 92 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.

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  1. U

    Electromagnetic field vs electromagnetic wave "radiation"

    ( @jrmichler wrote to me: "SHEESH, more fearmongering. But please do not bring these conspiracy theories to PF." You write to wrong person, you and moderator of PF can send a email to scientists in WHO/International Agency for Research on Cancer (IARC) and ask them why they make this...
  2. F

    I Current's Effect on Electrical Arcs

    Hello, I figured this belongs more in a physics thread than an electrical engineering thread, but please advise I am wrong. I am having a hard time finding the correlation between the amount of electric AC current flowing in a conductor and its affect on allowing an electric arc. Obviously the...
  3. Q

    I What causes skin effect in AC currents?

    My assumption has been it is the electromagnetic field starting from the center of the wire that pushes the electrons outward. However, this would also be true of a DC current, but it isn't. So why does an AC current cause electrons to move toward the skin of a wire? I don't recall ever seeing...
  4. F

    B The historical war of currents in Mains Power Distribution: AC vs DC

    So, if I get it right, the basic argument goes like this: AC was preferred to DC because its voltage can be stepped up by a transformer. This limits losses while the current is transported from the production plant to the final user. The voltage is subsequently stepped down when delivered to the...
  5. A

    Biot-Savart equation for AC current

    The fact that the current changes in time should allow me to take it outside from the integral along the coil, since it is not a function of space. But I'm not sure about this assumption, is there something I'm missing or am i correct? Thanks
  6. Benjamin_harsh

    Current vs. Time in AC Current

    I always find voltage vs time majorly in case of AC current. What about current V time in AC current cases?
  7. I

    DC versus AC current in a coil

    Hello, am kind of new to all the physics stuff , and kind a terrible at maths but am trying my best to be good at it one day .So i was told to answer this question When a direct current of 2A is passed through a coil, the potential difference across the coil is 20V. When an alternating current...
  8. Efeguleroglu

    Why RMS for the average voltage in AC current?

    We write rms formula as $$v_{rms}=\sqrt\frac{\int_a^b[f(x)]^2dx}{|b-a|}$$ I know if we take arithmetic mean average voltage will be 0. So we want all voltage values to be positive. Why don't we do that: $$V_{average}=\frac{\int_a^b\sqrt{[f(x)]^2}dx}{|b-a|}$$ That's first what I did...
  9. S

    AC Current versus AC Voltage on the Neutral Wire of AC Mains

    Sir how can one explain with the help of an analogy to a grade 10th student the reason behind not getting a shock on touching the neutral wire of the household AC circuit, even though the current flows alternately through live as well as neutral wires.
  10. Zack K

    How exactly do inductors work in an LC circuit?

    I understand Faraday's law and about induced electric fields created by a changing magnetic fields, etc. But what causes the current to oscillate in an LC circuit, with no battery? If you picture that there is current going into an inductor, and that current is decreasing over time, then you...
  11. N

    A Solving Maxwell's Equations for Electric Field of AC Wire

    I'm having trouble figuring out how to solve Maxwell's equations for the electric field of an AC wire. I assume the Voltage waveform in the wire is 120sin(60t). This circuit only has a 14ohm heater in it, according to Ohm's law I=V/R. The current is equation to I(t)=120sin(60t)/14 It is...
  12. T

    Understanding current measurement on an irregular waveform

    I hoped to use a Keithley 2400 source meter to generate a ~120Hz AC signal by outputting a 2-point sweep from 1A to -1A on an infinite trigger. The waveform image is attached below. The end goal is a resistance measurement for bulk semiconductor materials, we prefer AC measurement to avoid...
  13. jlmccart03

    Finding frequency of an AC current sin wave?

    Homework Statement An AC current is given by I= 475 sin( 9.43 t), with I in milliamperes and t in milliseconds. Find the frequency. Homework Equations w = 2pi*f The Attempt at a Solution I got 9.43/2pi which is 1.5 Hz, but that is wrong. I honestly have no idea what to do to find the Hz.
  14. S

    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...
  15. B

    AC current / circuit simulation software

    I'm looking for software that can simulate an ac circuit. After a quick google, I found several free online services (which I will try out). What I was wondering though is if anyone had some advice concerning my selection. A brief list of requirements: accurate simulation of different conductor...
  16. Arup Biswas

    Good books for learning AC current?

    I'm a 2nd year Physics student! I want to learn electricity from it's absolute basics! Like AC current, how it is formed, where is formed etc. Please suggest me books which will tell me about the theory in details along with required mathematics too!
  17. F

    Measuring AC current with an oscilloscope.

    I have a technical question, for research purposes. I have LED that we probe in AC mode. To measure the applied voltage in AC and the light-response in AC is no problem. However I would like to measure the current going through the device as well and I would like to link it to an oscilloscope...
  18. P

    What is the role of displacement currents in a circuit?

    Please help me with this. I am having a hard time understanding the role of displacement currents in a circus. The common knowledge is actual current is the movement of electron in a circus. Now, if there is a gap and an AC source, there would be an electric displacement field and a displacement...
  19. Matt2623478600

    Can I Use AC to Power DC LED Light Bars for Stage Production?

    I need guidance in the explanation of utilizing LED light bars for a different function then designed. I do stage production, sound and lights for concerts and would like to adapt these LED light bars to "blind" to crowd. My issue is that each light bar operates 12-30 Volts DC @ 300 Watts. In...
  20. AsadQZR

    How does turning off a light bulb affect the entire electric grid?

    Hello Physics Forums, this is my first post! I wanted to know how the current electrical grid system works. I mean, not in terms of creation, transmission, and distribution, but rather, how you would draw it on a circuit diagram. I understand that an AC current is generated at the power factory...
  21. Buggsy GC

    Why does AC have less copper loss than DC

    Hi there everyone, I'm doing some study on electronics and the section on the advantages of A/C over DC mentioned that AC has less copper loss (I^2 x R), But to me this seems contradictory to the skin effect. Could someone please tell me why AC has less copper loss.
  22. A

    Flux Pinning in a type 2 SC Using an AC Electromagnet

    When a supercooled type two superconductor is subjected to a static magnetic field, the superconductor pins to the flux of the field (the mixed-state meissner effect is apparent). What happens if it is subjected to a continuously changing magnetic field, assuming the superconductivity takes...
  23. T

    Skin effect and magnetic field of a flattened conductor?

    A conductor with a large high frequency AC current causes a "Skin Effect" meaning that most of the current flows at the surface of the conductor. What does the skin effect look like if you have a conductor with one side flattened? And what does the resulting magnetic field look like? See...
  24. A

    The highest frequency of ac current?

    I heard about a research where ac current is generared in metal covered nanotubes exposed to visible light, the same way as it does in receiving tv antennas. Isn't there a limit to how quickly electrons can accelerate on a metal surface (because of inertia and maybe some extra factors) to...
  25. Carlton Brown

    How can i generate an 8 hertz AC current from 60 hz AC

    Hello there. i would like to request some help please in the design of my meditation pyramid. If you can help me out i'd be greatly appreciative thank you. I would like to set up an 8 hertz oscillating magnetic cycle around the pyramid. Why? because i wish to entrain higher alpha brainwave...
  26. G

    Does a photo-resistor create an AC current?

    I'm a high school physics student. I want to do an experiment to see what happens when a high frequency alternating current goes through a magnet. To create the high frequency alternating current could a photo resistor do that for me? Does the photo-resistor create an alternating current with a...
  27. ernd59

    AC current / volatge with a mosfet in Ltspice

    Hi, my Voltage Multiplier Simulation does not work properly the first transformer is working just fine, the second one does not really seems to work, for the second transformer i tried to creat AC current with a mosfet, but i think I am doing it wrong :/, can you give me some tips how to...
  28. 1

    Does current flow in both wires or in one in our homes?

    If we have a source of AC current with two terminals ( A and B ). We connect a device with this source. Now we say that one wire is live and other is neutral. But my question is that, how one wire is neutral. As we say that in AC current the terminals change the polarity. Its mean that some...
  29. J

    Does an AC current have to cross zero?

    So my question is simple. If the current doesn't change sign, is it considered AC or DC? I seem to recall we called it DC when I briefly saw it. However after a quick google search I'm confused. Some said that for example an AC signal offset with a DC signal to show this behaviour should be...
  30. F

    Mutual force between AC current carrying wires

    Hello Everyone, I have wondered about this for a while but have not found a book or article that deals with this topic. Two wires carrying DC currents directed in the same direction attract each other (repel if the currents go in opposite directions). What happens if the currents in the two...
  31. A

    Average Electron Drift Distance with AC Current

    Homework Statement A metal wire with 1023 free electrons per cubic centimeter is carrying 60 Hz alternating current with a maximum current density of 100 amps/cm2. a) Write an expression for the average electron drift velocity as a function of time (vd as a function of time). b) What is the...
  32. G

    Does AC current pass through perfectly shielded box?

    Hello. I've recently have a lot of question of building Faraday cage for our high voltage gas discharge lab. I think this question is a kind of fundamental question for such a job. Let's say I would make perfect Faraday cage with perfect shielding or have metal plate of infinity transverse...
  33. G

    Permeability in ferromagnetic material (AC)

    Homework Statement The following coil-wound core (core length = L , Gap length = lg, cross- sectional area = A , core permeability = only hysteresis graph is given, N = N turns) is driven by a Voltage source, is known that the current in the coil is 60hz AC. Determine...
  34. S

    AC Current Source: Build an Op-Amp Circuit for µA RMS

    Hi everybody, As part of my research at UCSD, we are trying to measure Hall resistance of some materials. And to do that we need to send an AC current. So I wondered how we could easily build an ac current source, probably based on op-amp. I know there is the Howland circuit (current pump), but...
  35. J

    Vacuum tubes and electronic oscillators

    I've been reading up about vacuum tubes and (more specifically) the Audion, and how they were used for instruments/amplifiers. This isn't anything I'm learning about on my degree, just things I'm reading up on myself so forgive me if I'm a little slow to grasp some parts. I understand how the...
  36. W

    Losses in AC and DC power tranfer

    Hello, I have forgotten most of the electricity physics we studied and I have problem describing/understanding a concept. Does AC current produce less loss than a DC current? I found this statement in a website: "AC electricity loses less power over power lines than DC"...
  37. RAHIL008

    AC current through AC equipment

    I wonder if AC current follows Sin wave and go through negative and positive cycles alternately, why don't AC equipments, like a bulb, get off and on - off and on...
  38. mostwantedmani

    Increase the frequency of AC current

    How to increase or decrease the frequency of AC current linearly? Suggest me some ideas
  39. D

    AC question -- How does AC current "reach" its load?

    How does AC current "reach" its load? If the electrons/fields/charges are oscillating (reversing direction 50 or 60 times per second) instead of traveling in one direction like DC does, how does current flow and reach the load in a circuit? I have read some articles but couldn't find an answers...
  40. N

    Engineering Coupled RC circuits with AC current source

    Homework Statement Hi, I already asked a question close to this, but now I have different conditions. This is the circuit C_1 = C_2 \\ R_1= R_2 The current is an AC , and I would like to know the voltage at R_1 and at R_2 I made some progress but I do not really know hot to continue...
  41. D

    Calculating Current Density Distribution in Proximity Wires

    Hello. I'm floundering. What is the right way to formulate a problem of calculating the current density distribution across the wire's cross-setion, taking into account eddy currents? If the Maxwell's equations are not the way to go, what is? What should be the boundary conditions or any...
  42. L

    Functioning of AC current in simple terms?

    Hi, Thank you for reading this. I understand the functioning of DC current. You create a potential difference and the electrons flow from the power source through the electrical appliance (thereby, powering it) and flows back, completing the circuit. But, in AC, the electrons...
  43. K

    AC current and incandescent bulbs

    In my class we did an experiment where we measured the flicker frequency of an incandescent bulb and a CFL bulb (powered by a 60hz wall plug) using a photodiode and a oscilloscope. We were then asked some questions about the sinusoidal curves that were produced. 1. The incandescent...
  44. B

    How to safely create static electricity from AC current

    Is there a simple way to "make" static electricity from an AC outlet? Looking for a way to make my hair stand (what is left of it) on its end for an experiment. Thanks for your comments in advance.
  45. G

    Question: Why does AC current change through a transformer?

    Hello physics friends! I have a question about AC current I hope you can help me understand. So I know that putting AC through a transformer will raise or lower the voltage, but because power has to be kept constant, the current changes in the opposite direction. But according to Ohm's law...
  46. M

    Intuitive reason for the capacitors/inductors in AC current

    Hello, I am wondering, why conceptually an inductor would have a large inductive reactance at high frequencies, and why they are large for capacitors are low frequencies.
  47. B

    Shielding a single AC current carrying wire.

    I was thinking whether it was possible to shield a portion of a circuit that has only a single conductor without a return path. The frequency is high enough for the Earth's capacitive impedance to be low. Is my assumption then correct that the induced voltage in the shield will create a...
  48. R

    How does AC current alternate and is energy replenished in a circuit?

    I know that in AC the current switches between +ve and -ve 50 times a second in the case of mains electricity for the UK. However I was confused about how it alternates, as in when it swtiches how far do the electrons travel before it switches again. I was also told that in a circuit the...