What is Current: Definition and 1000 Discussions

An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving particles are called charge carriers, which may be one of several types of particles, depending on the conductor. In electric circuits the charge carriers are often electrons moving through a wire. In semiconductors they can be electrons or holes. In a electrolyte the charge carriers are ions, while in plasma, an ionized gas, they are ions and electrons.The SI unit of electric current is the ampere, or amp, which is the flow of electric charge across a surface at the rate of one coulomb per second. The ampere (symbol: A) is an SI base unit Electric current is measured using a device called an ammeter.Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers. In ordinary conductors, they cause Joule heating, which creates light in incandescent light bulbs. Time-varying currents emit electromagnetic waves, which are used in telecommunications to broadcast information.

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  1. Engineergn

    Snail Fan Motor High Current Issue

    We producing industrial steam boilers. We also produce snail fans for our boilers. The problem is our fan blades are a little bit heavy for our motors until blades get warm. "We can't use more powerfull motors cause of energy saving." We control our fan motors via drivers and our fan blades...
  2. S

    Battery circuit current flow when charging

    I would like to know when a alternator is charging a battery is the current flow a series opposing circuit......?
  3. Evari5te

    Solving Current & Power in 4 & 3 Wire Circuits

    My thoughts were I could use mesh current analysis to derive equations for current hence power in each case in terms of ωC and R, set the equations for real power equal to each other and solve for R. While ωC are known I opted to leave them as letters thinking this might make life easier when...
  4. PhysicsTest

    Optimizing an Op Amp Current Sense Circuit: Are the Calculations Correct?

    TL;DR Summary: Trying to solve the op amp current sense circuit as per the schematic. I want to solve the below current sense op amp circuit, Are the calculations correct? As of now i modified the circuit by removing the capacitors, i will add them once the above circuit calculations are...
  5. Kyuubi

    Speed of Current in a coaxial cable

    I've found the inductance and capacitance per unit length in a long coaxial cable. I even clearly see that if I multiply the two, I can get the speed of light. How do I begin to find the current wave and its speed though?
  6. Kyuubi

    Current on Infinite Periodic LC Circuit

    I wrote down the equation of motion for In(t) and I'm trying to match it with infinite spring mass system equation solution. In the spring mass system, we consider A to be the equilibrium length of the springs, and we can thus write Xn(t) = X(nA,t) and put it back into the equation of motion...
  7. K

    Current through Flat Sheet or plate

    Current flow through a wire is considered (or assumed) to be flown uniform across the cross section of the wire (or is it more near skin? or at core?). However I wonder if that's the case with a sheet or plate or circular disc. e.g. If I apply voltage at two opposite corners of the square or...
  8. C

    Question about the Microscopic Model of Current

    Why do they say uniform conductor? Many thanks!
  9. S

    I Deriving expression for resistance in terms of current density

    Is there a way to obtain equation 9.42 (I is current, j is current density, and sigma is conductivity) in the following image (from Modern Electrodynamics by Andrew Zangwill, the part on electromotive force) besides using V=IR and substituting the line integral of j/conductivity for V? The...
  10. supak111

    Calculate current in a 120 VAC circuit with a series 10uF capacitor

    Hi can someone tell me please how much current is passed though below circuit: 120 AC 60Hz mains power going through a 10uF 500v capacitor in series
  11. B

    I Emission of light from incandescence of metals

    a. We know metals emit EM radiation upon heating or electric current. I'd like to understand more fundamentally how this phenomenon takes place, on the basis of the basis of band structure, and which electrons are involved ? b. Classically, charges emit radiation when accelarating or...
  12. G

    Power generated by this current source

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  13. F

    Engineering Use voltage nodal analysis to solve for the current flowing in this AC circuit

    Hi first time using this forum, I have some homework that I am entirely stuck on, can anyone help me with this question? I understand the placement of nodes, and that I need to convert complex numbers, but apart from that I have no idea what direction that I'm supposed to take in this. I don't...
  14. babaliaris

    How does Earth Ground "absorb" electric current?

    This is a topic that almost no one can actually explain from what I found on the internet. This answer https://physics.stackexchange.com/questions/74625/does-alternating-current-ac-require-a-complete-circuit/74999#74999 is the closest I found so far. The idea is how the grounded neutral...
  15. H

    B Voltage & Current: Explaining the Basics for Beginners

    This is a very basic beginner question but one which confuses me. We are told that voltage = current x resistance but I've also read that we can have a voltage without current. But, if current = zero, then if V = IR, V must be zero. Can someone explain where am I going wrong?
  16. A

    A Current status of Tom Banks' Holographic space time?

    Interested in Banks' HST these days, for discussion,here are some abstract and an email from L.Smolin. A recent conclusive paper as well https://arxiv.org/abs/2201.06988 The formalism of Holographic Space-time (HST) is a translation of the principles of Lorentzian geometry into the language...
  17. A

    A Current status of FR type Thought experiments

    Recently I've seen many fixed FR(or Wigner's friend) thought experiments.For example, https://arxiv.org/pdf/2011.12716.pdf is a zero-cited paper that presents a strenthened version of FR ,and claims to have solved its weaknesses.The author claims that it supports the idea that the "C"(for...
  18. A

    Calculate the probablity density and current density of a wavefunction

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  19. JH_1870

    A A question about current density in finite element analysis

    I know that if there is only one conductor providing the current density, then the current density can be used. But if you apply Maxwell's equation when there are multiple current sources, I don't know which value to use. This is not an analysis using a tool, but a problem when I develop the...
  20. JH_1870

    A Relationship between magnetic potential and current density in Maxwell

    I am currently studying to solve Maxwell's equations using FEM. I have a question about Maxwell's equations while studying. I understood that the magnetic potential becomes ▽^2 Az = -mu_0 Jz when the current flows only in the z-axis. I also understood the effect of the current flowing in a...
  21. S

    B Phase Difference of Current & Voltage: Capacitors, Inductors & Complex Numbers

    how does capacitors and inductors cause phase difference between current and voltage? how does complex number come into play to explain the relation between phase of current and voltage?
  22. Skarki

    Find the current using jω method

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  23. A

    A Why is there no saturation current for Si photoanode during OER?

    The Si/Ni photoanode was prepared by sputtering Ni on n-p homojunction Si substrate, and the electrolyte was KOH solution.
  24. kma

    How accurate is a multimeter when measuring current

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  25. unoonu

    Relative Velocity Against the Water Current

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  26. PhysicsTest

    LED Peak Current: Know Nominal & Peak Currents for Vehicle LEDs

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  27. hagopbul

    A question about the current SAT standardized tests

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  28. besebenomo

    Moving bar enclosing a changing magnetic field generates a current

    The amplitude of ##\vec{B}## is given by: $$B(x) = B_{0} - B_{0} \frac{x}{2l}$$ for ##0 \leq 0 \leq 2l## This was my attempts at finding the flux of B: $$\Phi(B) = (B_{0} - B_{0} \frac{x}{2l})(2l-x(t))l = B_{0}2l^2-2B_{0}x(t)l+ B_{0}\frac{x(t)^2}{2}$$ and the current: $$ i = -\frac{d...
  29. simphysics

    Current calculation of a Y-junction

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  30. L

    Current through ring in solenoid-ring system

    The following is my solution to this problem; I would appreciate some feedback, especially on part (b), which I have found the most challenging. Thanks. (a) Using Ampere's Law I get ##B=\mu_0 n i_1## where ##i_1## is the current through the solenoid, and since ##\phi=Li_1##, where ##L## is the...
  31. 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
  32. Salmone

    I Can current flow in an open circuit?

    I have two related but separated questions: 1. If I have an open circuit connected to a battery, let's say an alkaline battery connected to a straight wire and nothing more, once I connect the battery to this wire there will be for a short time a current in the wire? Since in the battery due to...
  33. G

    Is Moore's Law Still Relevant in the Age of Semiconductors and Robosourcing?

    I'm sure this gets asked a lot. CPUs and GPUs still kind of mystify me, since I do not know their science. It came to me after studying some computational linguistics that it might be possible that in the next 100 years, we might have smart-translating, smart-talking machines without a theory...
  34. S

    A Current Status of Electromagnetic Triviality

    I know how to calculate the standard Landau pole result at one loop suggesting that a quantum field theoretic treatment of the electromagnetic force in the continuum is trivial. I am wondering does this result continue to hold at higher loops, nonperturbatively or when electromagnetism is...
  35. LCSphysicist

    I Current theory of composite quarks and leptons

    "M. Shupe [Phys. Lett. 86B, 87 (1979)] has proposed that all quarks and leptons are composed of two even more elementary constituents:" (Griffiths) I am redoing the book of elementary particles from Griffths, and this exercise has showed really interesting to me. How is the currently status of...
  36. D

    Solar Sails -- What are the current limitations?

    What are the current limitations with solar sails and why are they not used with greater frequency? I have heard of hydrogen blistering -- is that a significant issue?
  37. shivajikobardan

    Comp Sci Current broadcast address+1 for next subnet network address?

    https://www.cisco.com/c/dam/en_us/training-events/netacad/demos/CCNA3v3Demo/PDF/lab_1_1_4.pdf This is the pdf I am studying from. This is not exactly what I need for my exams but it’s pretty clearly written and concept giving thing. 192.168.10.0/24 is given IP address to subnet. We need 4...
  38. G

    B Resonance state - Alternating current

    In alternating current, is the resonance state that the phase angle of the current is 0?
  39. greg_rack

    Current flowing through resistor in RLC circuit (C in parallel with L)

    Hello guys, LRC circuits with an AC source are having the best over me... had some confusion in class with respect to which method is best using(phasors diagram, reactances or complex impedances) which I am trying to desperately sort out before my exam; here I will show you my best attempt on...
  40. Mr Nobody

    How Can Eddy Current Drag Be Minimized in AC Generators?

    Hello everyone, I'm working on a home project to create AC current, using magnets (AC Generator). I understand the principles of how to generate AC current however, I lack the complex knowledge of the physics side. I have searched and watched various Youtube videos etc, but none of them answer...
  41. A

    RL Circuit Initial Current Simplification

    ##I_2 = \frac{V}{R_3 + R_2}e^{-t/\tau}## ##I_2 = \frac{50}{19.4(2)}e^{-t/\tau}## as t goes to 0, ##I_2 = \frac{50}{19.4(2)}## = 1.29 Amps which is not the answer.
  42. P

    Parallel RLC Admittance, Current and Power Vector Diagrams

    (An even longer-winded version was written and deleted out of mercy.) Assume an AC voltage at zero degrees applied to an ideal parallel RLC circuit. For a predominantly inductive circuit, the vector diagram for current should show the supply current in the fourth quadrant (i.e. with lagging...
  43. Orodruin

    Insights Symmetry Arguments and the Infinite Wire with a Current

    [url="https://www.physicsforums.com/insights/symmetry-arguments-and-the-infinite-wire-with-a-current/"]Continue reading...
  44. J

    Solving for x in Circular Current Equation

    The second equation gives the magnetic field at a point away from the center of a circular current. If we multiply this by the the area we get a function for the magnetic flux. We have an increasing current which induces an increasing magnetic field. Now just solve for x in the second equation...
  45. L

    Solving Equation to Analyze Steady State Current

    I set up the equation ##V-iR-L\frac{di}{dt}=0##, with ##i(0)## and by solving it I got ##i(t)=\frac{V}{R}(1-e^{-\frac{R}{L}t})##. Then, since the steady state current is ##i_s=\frac{V}{R}## I imposed the condition ##i(t_1)=\frac{9}{10}\frac{V}{R}\Leftrightarrow...
  46. N

    Pourbaix diagram and current voltage curve

    I have a chemistry project and my research question roughly translates to: What is the effect of the different metals electrolytic nature on iron corrosion? (In french: Quel est l’effet de la nature électrolytique de différents métaux (cuivre, aluminium, magnésium) sur la corrosion humide du...
  47. Mr_Allod

    Total Josephson current through junction with magnetic field

    Hello there, I am given a diagram of a Josephson Junction like so: With a magnetic field ##B = \mu_oH## in the z-direction. I'm reasonably sure ##d_x,d_y,d_z## are normal lengths, not infinitesimal lengths although that is up for debate. Using the above equations I rearrange the expression...
  48. BnayaMeir

    Surface Current and Electric Field

    Hi everyone! I'm pretty new in this forum, I found the topics here very relevant to my physics course. And here is my question: Given the following drawing, two infinite sheets (in y and z axis) of ideal conductive material. their thickness is infinitesimal (dx->0). The electric field is...
  49. ErikZorkin

    I Simulating physics: the current status of lattice field theories

    I recently watched this video by David Tong on computer simulation of quantum fields on lattices, fermionic fields in particular. He said it was impossible to simulate a fermionic field on a lattice so that the action be local, Hermitian and translation-invariant unless extra fermions get...
  50. C

    Why is current defined as the rate of change of charge?

    Homework Statement:: This isn't a homework question but just a theoretical questions. [mentor’s note: moved to a more appropriate forum for theoretical questions.] I know that current is defined as the rate of change of charge per unit time. i = dq/dt This makes sense for a capacitor which...
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