Current Definition and 1000 Threads

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. gurbir_s

    I Angular momentum associated with a current carrying circular wire

    How should I calculate the angular momentum carried by a current carrying circular wire? Is it correct to consider the angular momentum of the electrons moving with drift velocity? Like ##L = n m_e v_{drift} r## where ##r## is radius of the loop, and ##n## is total number of electrons moving in...
  2. L

    Discharging a capacitor -- Calculate the current as a function of time

    Hi, I am not sure if I have calculated the task b correctly. I always interpret an open switch as an infinitely large resistor, which is why no current is flowing through this "resistor". So there is no current in the red circle, as it was the case in task part a, but only in the blue circle...
  3. ananonanunes

    Finding Current in Resistors & Charge of Capacitor

    Suppose the switch has been closed for a long time so that the capacitor is fully charged and current is constant. a)Find the current in each resistor and charge Q of the capacitor. b)The switch is now opened at t=0s. Write the equation for the current for the resistor of 15kΩ as a function of...
  4. S

    I Can Conducting Current Through a Bar Magnet Cause Movement?

    Following the Picture below, If I Conduct current through Permanent magnet Bar and hold the battery still. Will the magnet move in any direction ? Thank you.
  5. Jarvis323

    Current and Future AI Threats to Humanity and the Human Response

    There has been an explosion of discussion among experts about the evolving/growing dangers of AI and what to do about it. This debate has gone public, largely due to the recent success of generative AI, and the rapid pace of improvement. As an example, AI models which can generate images based...
  6. MatinSAR

    Current in a circuit without external resistance

    It shows 0 and it's obvious why. I have another question. Can I say that in this circuit the current is maximum and it equals to ##\frac ε r = 2A##?! Someone asked me this question: Are A and B two ends of the wire? If yes, Why is there current in the wire even though the potential difference...
  7. J

    How does the presence of a cube resistor affect current flow in a circuit?

    I would think that it is 2 A (6/3 because there are three wires the current can go to), but this does not seem to be correct.
  8. P

    I What is the benefit of measuring both direct and reverse current?

    What is it's benefit?
  9. G

    Power dissipated by a resistor on a coaxial cable

    I need help with part c. My solution: Is there an other way to do this other than dimensional analysis? P.S "dr an infinitesimal radius", it ofcourse should be dz.
  10. G

    Surface current on a spherical superconductor

    I need help with part b. My solution: Have I done it right?
  11. Astronuc

    History History of Railroad Safety - Spotlight on current derailments

    The recent spate of train derailments has put the spotlight on derailments and railroad safety in general. Railroads are generally a safe means of transporting cargo, including hazardous chemicals, and in fact railroads are safer than a decade or two ago. Yet, one catastrophic accident...
  12. G

    Using complex numbers to solve for a current in this circuit

    First I solved 4+j3, which I squared 4 and 3 to equal 16 and 9 then I added them to get 25 and then I got the square root of 25 = 5. Then I plugged it back in to the equation. [50/(5)(50)+100] x 150 to get 50/350x 150= 1/7(150)= 21.42. I've attached the correct answer.
  13. J

    Determining Current Direction in a Charging RC Circuit

    After the switch is closed, current flows clockwise from the battery to resistor R1 and down through the switch. I don't understand the reasoning for the following: the current from the capacitor flows counterclockwise and down through the switch to resistor R2. How do I determine the direction...
  14. T

    I Are voltage and current waves in transmission lines an artifice?

    The operation of a transmission line is based on the axial propagation of electromagnetic waves between the two line conductors. However, the study of the transmission lines does not focus on E and B waves but on voltage and current waves. It is considered that there are resistance...
  15. PhysicsTest

    Engineering Is My Understanding of the Current Amplification Circuit Correct?

    I have taken portions of a schematic for amplifying the current I1, this I1 current is the phase current from one of the legs of the inverter. The output vout1 is the amplified voltage, again given to a micro which has internal opamp. Is my circuit understanding correct? When I give I1 = 10...
  16. PhysicsTest

    Engineering Voltage and current calculation of circuit

    I am trying to find voltages and currents of the below circuit, 3.3 -22000*I2 - 2200(I2-I3) = 0 3.3 -24200*I2 + 2200*I3 = 0 -> eq1 -(10 - I3)*1500 - (I2 - I3)*2200 = 0 -15000 + 1500*I3 - 2200*I2 + 2200*I3=0 -15000 - 2200*I2 + 3700*I3=0 -> eq2 Solving equations 1 and 2 i get I2=0.38 Amps...
  17. abdulbadii

    Failed function within SMPS giving weak current

    What is the very common culprit component and what is its function within SMPS having weak current, far weaker than its rating while its voltage is always perfect?
  18. haha0p1

    Using Kirchhoff's law, deduce the value and direction of the current

    3 A+ 2 A = 7 A+ I I = -2A How the current can be in negative direction? If the sign if negative, doesn't it mean that the current will move towards the point P? Also If I am taking the 2A to be positive then Kirchhoff's law isn't satisfied as 5A≠7A
  19. 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...
  20. 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......?
  21. 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...
  22. 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...
  23. 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?
  24. 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...
  25. 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...
  26. M

    Question about the Microscopic Model of Current

    Why do they say uniform conductor? Many thanks!
  27. 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...
  28. 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
  29. B

    I Emission of light from incandescence of metals

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  30. G

    Power generated by this current source

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  31. 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...
  32. 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...
  33. 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?
  34. 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...
  35. 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...
  36. A

    Calculate the probablity density and current density of a wavefunction

    i have use time evolution operator to get the wavefunction at any time "t" as Ψ(x,t) = U(t,t1) * Ψ(x,t1) but i don't know how to calculate next part of the question
  37. 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...
  38. 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...
  39. 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?
  40. Skarki

    Find the current using jω method

    Summary: Current using jω method with 3 components in the following series : Resistor, capacitor and Inductor. I have the following information: R=1 * 10^3 ohm L = 0.5 H C = 0.1 * 10^-6 F v(t) = 230 * sqrt(2) * sin(2pi * 400 * t) All the components are in parallel as shown in the image...
  41. 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.
  42. kma

    How accurate is a multimeter when measuring current

    Hi. I want to ask a quick question, how accurate are multimeters? Like is every current detected on a multimeter a legitimate current or can it sometimes detect false currents, and can it miss any currents that are there? And how accurate are the values on there when it comes to what the current...
  43. unoonu

    Relative Velocity Against the Water Current

    vcanoe_wrt_ground = 3 m/s + (-6) m/s = 3 m/s - 6 m/s = -3 m/s Thus, if I understand this correctly, the rower will never reach his goal 36 m away as his canoe's resultant velocity is negative (i.e., his canoe is effectively going downstream even though it is trying to go upstream). My only...
  44. PhysicsTest

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

    I want to understand if LED's which are used in the vehicles have Peak and nominal current? This is to know the hardware design to support the LEDs with peak currents, if both peak and nominal currents are same we can design a single board else the hardware design shall also consider the peak...
  45. hagopbul

    A question about the current SAT standardized tests

    hello : i saw a sat book few days ago and noticed that it is only english and elementary math , i was surprised do you need to pass only sat to enroll in a university why there is no sat object , for example sat physics , sat math , sat chemistry ,...etc in order to help student with the sat...
  46. 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...
  47. simphysics

    Current calculation of a Y-junction

    Hello everyone! I've been trying to solve this circuit but there's something wrong. Firstly, I made a Delta-Y conversion so that1 and zA were in series, and so were z5 and zb. I really don't know if writing "I0=IA-IB" is correct, cause basically I0 is the current that flows between the nodes A...
  48. 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...
  49. 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
  50. 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...
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