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. Another

    What happens when electric current is distributed in the material?

    When supplying electricity to the material. the shape of the material may or may not be square. This material may be This material may be moisture materials or solid materials that may conduct electricity. I would like to know the travel characteristics of electric currents and the potential...
  2. Wrichik Basu

    Other How faulty is the current education system?

    Having spent five months as an undergraduate with physics major, I found that there are two types of students who come to study physics: 1. For a job, and 2. For pursuing research. This thread is concerned with the second type only. Among many other problems, here are two that have concerned me...
  3. P

    Why is the output current of a transformer fixed?

    Im confused about how the output current of a transformer is fixed ie can be calculated by the law of conservation of energy only...(VI)in = (VI)out ? If the secondary coil is part of a circuit, and the secondary voltage is defined by V1/n1 = V2/n2, then the current in the secondary circuit...
  4. E

    Electric current and resistance question

    Homework Statement:: problem solving You build a wire by combining an 8 inches copper wire with a 10 inches nichrome wire. If their combine resistance is 10 kΩ, find the cross section area of both wires. The nichrome wire has twice the area of the copper wire. Homework Equations:: I = V/R...
  5. J

    Introductory Circuit Analysis—power ratings

    I am going through "Circuit Analysis for Dummies". On pg 18, it says, "If you calculate the power dissipated as 0.1 watts, then a 0.25-watt resistor can handle this amount of power. A 0.125-watt resistor should be able to handle that amount as well, but when it comes to power ratings, err on the...
  6. Z

    Electrical current in semiconductors

    When a voltage is applied to a semiconductor at RT, the thermally excited electrons in the conduction band can move freely, similarly the hole that is generated in the valance band. Suppose we drop a voltage across the semiconductor. The electrons in the conduction band moves towards the...
  7. R

    Vector potential of current flowing to a point from all directions

    I am having problem with part (b) finding the vector potential. More specifically when writing out the volume integral, $$A = \frac{\mu_0}{4\pi r}\frac{dq}{dt}\int_{0}^{2\pi}\int_{0}^{\pi}\int_{0}^{?}\frac{1}{4\pi r'^2} r'^2sin\theta dr'd\theta d\phi$$ How do I integrate ##r'##? The solution...
  8. D

    Voltage and current as functions of time for a series RL circuit

    I already found ##I(t)## using Kirchhoff's laws, I got the equation ##V-RI-L\frac{dI}{dt}=0\Rightarrow L\frac{dI}{dt}=V-RI## then I solved the differential equation getting ##I(t)=\frac{V}{R}\left[1-e^{-\frac{R}{L}t}\right]##. My problem is founding the voltage as a function of time ##V(t)##, I...
  9. A

    Frequency in an AC circuit given capacitance, voltage, and current

    By combining the formula for the reactance of a capacitor with Ohm's Law for a capacitor, I can solve for angular frequency, and divide by 2π to find frequency. The resulting equation is: f = I/(2π VC) Using the given values, I end up with 5.2 kHz, instead of the correct answer of 5.2 MHz. I...
  10. M

    Engineering AC circuit: Find the current through the inductor & capacitor

    Hi! I wonder if it is correct. Can someone confirm (maybe with a software) ? I(L) = I2 I(C) = I2 - I3 -- Thanks.
  11. Elbraido

    How do we derive this forumla I=nqAv for current?

    Can someone tell or lead me to how we derive this forumla I=nqAv for current?
  12. W

    I How to derive the currents of Z boson and the EM current?

    I am a student minor in physics and I am taking this course of particle physics. And I have been lost since the Non-Abelian Gauge Theory which a few lectures before Electroweak unified Theory lecture. i am completely confused and overwhelmed by the math since the mid-term exam, since I was not...
  13. J

    How does the current divide in parallel inductors?

    I apologize using English fluently because I am not an Enlgish speaker. When I tried to solve this problem, I used current divider rule. So, $$i_o(t) = \frac{3}{3+5}*4e^{-2t} = 1.5*e^{-2t} A$$ However, This was wrong. The answer is $$ 1.5*e^{-2t} + 0.5 A$$ If I use $$V_O = L*\frac{di}{dt}$$...
  14. L

    Electromagnetic plane waves from a current sheet

    I have an infinite sheet (in lossless, homogeneous medium) of time-harmonic current in ##yz##-plane at ##x=−d##. The current density on this sheet is given by $$\mathbf{J}=\hat{z}J_0\delta(x+d)$$ ##δ(x+d)## is delta function. Moreover, there is a perfect electric conductor (PEC) half space at...
  15. C

    Combine 3 Eqns for Plasma in a Solenoid

    ∇p=j×B (eq. 1) K=nI BSolenoid=μnI⇒μK (eq. 2) ∇p=-2p0r/(a2) (eq. 3) Combining these three equations: j=-2p0r/(a2μK) (θ hat direction) Feel like this is too simple and might be missing a step any help would be much appreciated!
  16. D

    Finding the current and voltage for a resistor

    I tried to solve it by loop currents. So on the left mesh the loop current ##I_1## goes clockwise and on the right mesh the loop current ##I_2## goes counterclockwise. I ended up with the following equations: 1) ##V_1-R_1(I_1+I_2)-R_2I_1=0##; 2) ##V_2-R_3I_2-R_1(I_1+I_2)=0##. To find the...
  17. J

    When a short-circuit exists, how to find the current?

    I am not an English speaker, I apologize that I cannot use English well. I have a question calculating the IN. When the terminal a-b is short-circuited, is it right that the currents are zero at 2 ohm and 6 ohm resistances?(Because they are parallel with a short-circuit.) Also, because the...
  18. L

    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...
  19. M

    How to Determine the Noether Current for a Given Symmetry and Lagrangian?

    This is my first time dealing with scaling symmetry, so I'm sorry if the following is fundamental wrong. My approach was the same as if I was trying to show the same for translation or Lorentz symmetry. We have $$\delta\phi(x)= \phi'(x')-\phi(x)=...
  20. fight_club_alum

    Why Does an Inductor Store Energy After No Current?

    I calculated all the required in this problem correctly but can't understand why the sum of energy extracted and absorbed is not zero. They are: >0: 0J 0 <=E<=25: 4t^2 J 25 <= E <= 50: 4t^2 - 0.4t + 10 * 10^-3t J E > 50: 0 J Does that mean that an inductor stores energy even after there...
  21. R

    Explaining Mesh Currents: Understanding the Relationship between i1 and i2

    Here's my work. I have the correct answer, but I'd like to know why this only works for (i1-i2) plugged in for i_delta as opposed to what I initially put: i_delta = i2-i1. You can see this in the blue text above versus what I originally had in red.
  22. babaliaris

    Why does voltage = energy/charge?

    When you say ##i = \frac{dq}{dt}## it makes sense since current is the flow of charge over time. But why was voltage defined as ##v = \frac{dw}{dq}## ? What made physicians define it in this way? Is there a mathematical way that can lead to this definition or did they define voltage just on the...
  23. S

    3 phase alternator is generating a voltage, but no current

    I made a permanent magnet alternator out of a 3hp 3 phase induction motor. I am getting voltage, but no current at all. The alternator is wired delta and feeds a capacitor bank wired in a wye, to create a neutral. I have even tied the neutral into the alternator and still no current. I connected...
  24. garthenar

    How Does Coil Configuration Affect Current in LR Circuits?

    is the equation I found in the book for the current through an LR-circuit. The problem is I can't find anything in the text I have that deals with resistors in series vs parallel, if a coil acts as a short, etc. So can I ask you... 1) is this equation valid for both resistors in parallel and...
  25. PainterGuy

    Lenz's law and instantaneous change in inductor's current

    Hi, I will use this text for my question: https://imagizer.imageshack.com/img921/1874/nUBPY6.jpg Source: https://www.electrical4u.com/lenz-law-of-electromagnetic-induction/ The text says that when the north pole of a magnet approaches the coil, the induced current in coil is such that it...
  26. S

    How do I get the Current to be closer to 510uA instead of 1mA?

    Homework Statement: Calculate V7 and Is, I5 in the network below. Show your work. Homework Equations: Ix=(Rt/Rx)*I , (R1*R2)/(R1+R2)=parallel resistors. I=V/R, V=I*R, R=I/V, Vx = Rx*(E/Rt) Hi there everyone Sevarin here and I am asking for some help on this question i have been stuck with for...
  27. F

    BJT Transistor Collector Current

    I’ve attached an image below of a section from my textbook and some circuit simulations. The textbook gives an equation for the collector current in a bjt transistor. The simulation shows two circuits (with the same bjt transistor) that hav equal values for all variables present in the textbook...
  28. M

    Find unknown values of current in multi-loop circuit

    So I'm going over my review questions/notes provided by my professor for the upcoming exam on Tuesday, and I came across an example problem that I THINK might be a typo, but I want to make sure I'm right. I'm not sure why the potential drop when crossing V2 is ADDED to the loop equation for...
  29. J

    Potential sweep vs current sweep for a Polarization Curve

    Hello, I'm trying to obtain a polarization curve for a fuel cell (two electrodes in HCl). From what I've seen in literatures, current is applied and the voltage is measured. Is it still the same to change the voltage and measure the current instead? For some reason our equipment only have the...
  30. harsh22902

    Flux & Physics: Explaining the Constancy of Flux

    This is an excerpt from a high school physics textbook. I don't understand the possible reason behind this statement. If we change something in the circuit say for example add a resistor , the current and hence the flux should change. Then why/how is this statement true?
  31. K

    What is causing the strange ground current loop in this motor circuit?

    In the attached picture, I’ve drawn a crude schematic of the motor circuit. It is fed from a switchgear feeding 3 total motors. The feed contains 2 parallel conductors on each phase and ground. The equipment ground reads 12a going back to the switchgear, 6a per conductor. From the starter to...
  32. W

    How to find the current and voltage in a circuit with current sources?

    Summary: Facing a circuit with 2 parallel resistors and 2 current sources (1 dependent, 1 independent). Trying to find the current, voltage, power delivered by the independent current source and power delivered by the dependent current source. I'm trying to start by finding the current i0 but...
  33. A

    Current: the speed of charges vs the number of charges past a point

    Current is determined as the amount of charge moving past a certain point of reference (like the point in a wire with current meter clamps around it) in 1 second. This got me thinking , so in a classical resistive load situation with Ohm's law there would be two ways to increase the amount of...
  34. A

    Plasma current direction in the presence of an external field

    A simple question, I read that the particles in a plasma (protons , electrons) travel along the B field lines in a plasma which I know and they loop around the field lines each in opposite direction (clockwise, anticlockwise ) but both in the same direction. My question then is this. If I have...
  35. samudra

    I What is the current state of research on the nature of Time?

    As a non-Physics major, like many others, I read science-fiction, hard science-fiction, have undergraduate/graduate courses on Astronomy and college physics. I also participated in R&D that produced electric rockets able to power small space vehicles (very slowly, but surely). I deal with...
  36. F

    Engineering Determine the shunt field current in a magnetic circuit

    Problem Statement : Here's my attempt : * By assuming that the fringing and leakage effects are ignored. I find the flux density , the permeability and the reluctance of the iron , but then I get stuck . Any help would be greatly appreciated .
  37. fight_club_alum

    Determining the voltage polarity of the independent current source

    I am so sorry if I am posting this in the wrong forum; it is just not a homework problem, and I can't find the right place - it's more of a study help question.
  38. R

    Using Current and Voltage Dividers

    Can anyone explain how to go about this? I don't understand the solution, which says: A) Find the equivalent resistance (10 ohms). Find the voltage of the current source (4.2*10 = 42 V). Use a voltage divider to find vo = 42*(20/(10+20))=28V. My question is why do we need to add 10, which is R...
  39. Sid55

    Schottky diode with the correct voltage and current rating

    Non-isolated boost converter Input Voltage: DC8.5V to 50V Output Voltage: DC10V to 60V Max. Ouput Current: 12A Frequency: 150KHz
  40. E

    Is the current through the electrolyte double that through the circuit?

    Suppose, just for explanation purposes, we have an electrolyte of Na+ and Cl- ions connected to an external circuit with an ammeter which reads 96500A. In 1 second, we expect 96500C of charge to flow out of the cathode as 1 mole of Na+ ions are reduced, and the same amount of charge to flow...
  41. C

    Extremely high current effects in semiconductors

    So, let's assume in a theoretical case we have a (semiconductor but not necessarily) device, e.g. a MOSFET, that is perfectly cooled and has zero heat resistance (infinite thermal conductivity), and that it's connected to a perfect heat sink (theoretical abstractions for now, I will come back to...
  42. S

    A Effect of the driving current on the divergence values of laser diodes

    Dear readers, What happens to the divergence values of a laser diode (along and perpendicular to the emitting surface) when the driving current is increased or the output power is increased? Does the divergence: Increase along one axis? Increase along both axes? Decrease along both axes...
  43. lalallaland

    Two cells in series with internal resistors -- calculate the current

    Can somebody explain this please? I don't understand this.
  44. D

    Calculating Spatial Current in Resonant Inductors

    Hello, I would like to replicate the results from the paper "wireless power transfer via strongly coupled magnetic resonances", but I'm having trouble interpreting their equations. I'm creating a MATLAB script to do so. In the paper, they get to a point where L and C are to be calculated in a...
  45. R

    Finding Equivalent Resistance, Current, and Voltage across a resistor

  46. mpulis

    Electrical Increasing current in an intercom circuit

    Hi, I have purchased an electric lock some months ago. Now I purchased an intercom system which is rated at 1.2Amps. The cabling is rated at 1Amp. The lock is working sporadically. I guess it is because of the current. Is it possible that I boost the current received? Maybe through a relay? So...
  47. jisbon

    Deriving expression for magnetic field at point P due to current

    So I think I do understand how to do this, but the thing is my answers are always incorrect. Will need some guidance/help on this. ##B =\frac{\mu_{0}I}{4\pi}\int\frac{dysin\theta}{r^2} ## ##y = Rtan\phi## ##dy = Rsec^2\phi d\phi## ##B = \frac{\mu_{0}I}{4\pi}\int\frac{dysin\theta}{r^2} =...
  48. U

    Current induced from a changing magnetic field

    This question is motivated by Problem 7.12 in Griffiths Electrodynamics book. I have not included it in the homework section, because I have already solved it correctly. However, I question whether my solution which agrees with the solution's manual is correct. Relevant Equations: $$\Phi =...
  49. A

    Calculating the temperature of a conductor from the current through it

    I'm not sure if this is the right place for this but I have a question about the relationship between current through a conductor and the heat dissipated by the material. Given the current, resistance, and specific heat of a material as well as the specific spatial dimensions is there a way to...
  50. C

    Induced Current In a Tilted Square Inside and Outside a Solenoid

    Plot for the ring ^ Calculations for the Square ^ Plot for square without cosg on the outside calc ^ Plot for square with cosg on the outside calc ^ As can be seen the formulas for the square conductor do not connect at R, which I'm not sure if they should or if they should not as in this...
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