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. A

    Source transformation, current & voltage sources

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Hi, I was working on a the source transformation and i got to the part where there are two current sources in the circuit. The current sources were added together (giving they were going in the...
  2. H

    I Why probability current = 0 at infinity? Why must wavefunction be continuous?

    Q1. Why is the probability current ##j(x,t)=0## at ##x=\pm\infty##? (See first line of last paragraph below.) My attempt at explaining is as follows: For square-integrable functions, at ##x=\pm\infty##, ##\psi=0## and hence ##\psi^*=0##, while ##\frac{\partial\psi}{\partial x}## and hence...
  3. M

    Magnetic Field Computation from Thick Rectangular Conductor

    Hello, and thanks in advance for taking a look at my question. Generally, I am trying to make a railgun force model. Since railguns depend on the magnetic field created around the rails (and the resulting Lorentz force) I need to model the magnetic field created by the current that flows...
  4. Arman777

    Max values of current and charge using differential equations

    Homework Statement Homework Equations Circuit Equations. ##U_C=Q^2\2C## ##U_L=Li^2\2## The Attempt at a Solution For (a) I said ##100J## .But I think it might be ##200J## too.Here what I did; ##U_t=Q^2\2C## and I put ##Q=0.1C## and we know ##C##.Here I...
  5. AlphaLearner

    How does electric current flow through a conductor

    There's been a discussion going on since this following thread: Range of frequency of electromagnetic wave how electric current flow through a conductor. I need a proper clarity, does the electrons literally displace and flow or just the disturbance/energy travel through conductor making...
  6. satominari

    Why is there reverse current in diode equation?

    When deriving diode equation, it is assumed that there's no drift. But still, in the result, we have a reverse current which is a drift... I don't get where this comes from.
  7. Eric Willems

    Effects of high voltage & current on a large volume of water

    Hi, For a book that I’m writing, i need to know how to describe the following, if the situation described is ever possible, otherwise I'll have to come up with another scenario. A surge of high voltage electricity at a gas-insulated switchgear creates a flashover whose Breaker Current Failure...
  8. Shafia Zahin

    Voltage and Current in Ohm's Law

    Hello,one thing really confuses me ,in an open circuit the value of resistance is 0 and so due to v=iR the voltage also becomes 0 but my question is how can a current flow in a circuit where there is no voltage Difference? Please help. Shafia.
  9. Z

    Tip current in STM (fractional error problem)

    Homework Statement Suppose the STM tip current is given by i = aV e^{-A\phi^{1/2}s} a) Derive an expression for the fractional change in tip current as function of fractional change in tip spacing s. b) If \phi = 4V select a reasonable set of V values so that a 1Å increase in s will cause...
  10. K

    Current division in a series-parallel circuit

    Homework Statement Determine the current through each circuit element Homework Equations V = IR (Ohm's Law), The Attempt at a Solution I1 is .06A after plugging 6V and 100 ohms into V = IR, but I can't figure out the rest, because I don't know how the current splits. The left path obviously...
  11. A

    Circuit Problem -- Combining 4 resistors to make 95 Ohms

    Homework Statement 1. Use resistors of 30 ohms, 40 ohms, 50 ohms, and 50 ohms to create a circuit with a total resistance of 95 ohms. 2. Find the amount of current going through two of these resistors if the circuit is attached to a source of 12 v. 3. What would be the voltage drops for the...
  12. atommo

    Electron Spin and current-induced magnetic fields

    Hi, I'm currently investigating magnetic fields/their cause. This has inevitably led me to learn all about electrons. Here I want to post my understanding on electron 'spin' so people can correct me if I'm wrong/help others get a better understanding. So I watched this YouTube video for...
  13. Kara386

    I What Causes the Ring Current in Earth's Magnetosphere?

    Is ring current caused by gradient-curvature drift? I can't find a website that explicitly says that, they just call it 'longitudinal drift' and don't specify the mechanism, which I assume is particles drifting from one field line to the next - i.e. grad B drift and curvature drift?
  14. F

    Maximum current through a capacitor

    Homework Statement A 2200 µF capacitor is charged to a potential difference of 12 V and then discharged through an electric motor. The motor lifts a 50 g mass through a height of 24 cm. The capacitor is charged to 12 V again and then discharged through a 16 Ω resistor Determine the time...
  15. C

    Photoelectric effect : retarding potential with back current

    In the experiment of the determination of ##h## using the photoelectric effect produced by light emitted by led's there is the systematic problem of the "dark current" or "back current", i.e. the current caused by photoelectric effect on the anode of the system which is used in the expreriment...
  16. maxelcat

    Current in a capacitor question

    This is a question from an a level textbook. The R starts at 8k ohms (thought its not relevant) Switch S is closed - C fully charges up. Question:Switch S is opened. Explain why the current decreases and REVERSES direction in the ammeter. This is what I think. The decrease in current is...
  17. peroAlex

    Flux and Current of Magnetic Core With Air Gap

    I am a student of electrical engineering. This task appears in our textbook. However, there were no solutions provided. I tried understanding the task but got lost in the process. This is why I seek help here on this site. I would like to ask you for guidance and any sort of advice on how to...
  18. D

    Electronics - Have I found the transient current correctly?

    Homework Statement A step voltage of 120v is applied to a series CR circuit. C = (4x10^(-6))F R = (20x10^(3))Ω When the capacitor is fully charged the supply voltage is removed. Using KVL and Laplace transforms obtain an equation for the transient circuit current, given when t = 0, the voltage...
  19. Asmaa Mohammad

    The phase difference between current and voltage.

    Homework Statement An inductor (Xl = 40.2 ohm) is connected in series with a resistance (30 ohm) and and an AC source ( 10V , 80Hz) and the current flows in this circuit is 0.2 amp. How could you reduce the phase difference between current and voltage to zero without changing the value of...
  20. D

    Engineering Laplace tranforms, transient current series CR circuit

    Homework Statement A step voltage of 120v is applied to a series CR circuit. R = 20KΩ, C = 4µF 1. Deduce, using Kirchoff's voltage law and Laplace Transforms, an expression for the transient circuit current. 2. Using the equation obtained in 1. deduce the equations for the transient voltages...
  21. M

    Sizing a Solar Array To Boil Water

    Hello, I am having a hard time deciding the size of a solar array to boil water for a school project. Before putting any thought into the subject I simply thought that I would just take the wattage of the panels and add them up since they are added in both series or parallel and then select an...
  22. T

    Increasing voltage regulator current

    I'm looking to draw about 6A. I have an LM338 regulator that can supply up to 5A. Searching the internet I came across this schematic, So basically when the 1R resistor drops 0.6V then the transistor conducts the remainder of the current. I calculated my own values for those two resistors. Was...
  23. Buggsy GC

    How will the voltage, current and resistance be distributed

    I have a lab to work through tomorrow morning and i need to be able to explain how the voltage, current and resistance in the compound circuit diagram below is distributed, and write an equation which can be used to measure the total resistance of the circuit. I know that when you normally try...
  24. E

    LiPo battery peak current burst C rating

    Hi, as I know the burst C rating usually refers to the max current allowed for 10 seconds. if I need higher current for 1 second, I can do it? The heat is the problem here?
  25. nothing909

    Types of eddy current couplings

    Homework Statement I have a really simple question, state two types of eddy current couplings and state a flexible coupling, but I've been googling it for the last half an hour and can't find an answer. The Attempt at a Solution Can anyone tell me two types of eddy current couplings? I know...
  26. Kelsi_Jade

    After 14ms the current drops -- Find the capacitance at C

    Homework Statement Here is what I have so far. Am I going the right direction? If so, how do I go about finding the total current? Homework Equations See photo above. The Attempt at a Solution See above.[/B]
  27. D

    Exploring Induced Current in a Metal Coil

    Homework Statement The figure shows a metal coil labored as A. Heading torwards a region where a uniform static magnet field exists, poiting torwards the ground (hence X). The coil moves with the same constant velocity. As it enter the magnet field the coil will have an induced current in it...
  28. Benoit

    Eddy current loss in solenoid half-filled with magnetic core

    Hey ! Let's say I have a solenoid that is only half-filled with a magnetic core. Now I want to know what is the loss due to Eddy currents. First, I want to find the magnetic field with Ampere's law. With this kind of geometry, I'm not even able to apply Ampere's Law ! have of picture here of the...
  29. Cocoleia

    Magnetic flux, current and magnetic field confusion

    1. The problem statement Relevant equations: I am confused. When dealing with Ampères law: dl is supposed to be the length element? Like when we have Gauss' law for electric fields and we use a circular Gaussian surface, we have E(4πr^2)=Qenclosed/ε So in this case, when we have a circular...
  30. J

    Why a DC (direct current) component is undesirable?

    When choosing Line Codes (e.g. Bipolar or Polar formats) for transmission of bits over a communication channel such as twisted pairs, it is always desirable that no DC component is present for a particular choice. According to William Stallings (Digital Communication Book) "With a dc component...
  31. S

    Kirchoff's Voltage Law and Current Law --

    Homework Statement Homework Equations Using Loop 1, 2 and 3 The Attempt at a Solution
  32. BrainMan

    Induced Current in a Coil with Changing Magnetic Field

    Homework Statement A 5.0-cm-diameter coil has 20 turns and a resistance of 0.50Ω. A magnetic field perpendicular to the coil is B=0.020t+0.010t^2, where B is in tesla and t is in seconds. Find an expression for the induced current I(t) as a function of time. Homework EquationsThe Attempt at a...
  33. doktorwho

    Question regarding a magnetic field path around a gapped core

    Homework Statement ##l/l_0=100## ##S=3 (cm)^2## ##B_r=200μ_0H_c=2mT## ##R=10Ω## No current runs through the feromagnetic core. Calculate the charge ##q## that goes through ##R## from the moment in the diagram to the moment it is removed from the core. Homework Equations 3. The Attempt at a...
  34. 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.
  35. V

    Getting the magnetic field as a function of current

    Howdy, So, I'm curious, is there a general relationship between current input into an electromagnetic and the magnetic field that it generates in space? The trivial example is wrapping a wire around a rod, then sending a current through it which causes a magnetic field. My set up is a simple...
  36. A

    Finding the direction of current given a varying magnetic....

    Homework Statement Homework Equations μ0 In,e = ∫B⋅ds The Attempt at a Solution I really don't how to approach this question at all. Do you have to integrate counterclockwise around the loop every time? If the field was decreasing as y decreased, would you integrate CW or is it still CCW...
  37. whatphysics

    Finding closed loop gain and Ip and In current in op amp

    Homework Statement Finding closed loop gain and Ip and In current in op amp Homework Equations - The Attempt at a Solution I started by trying getting voltage divider for points between R1 and R2 as (R2/(R2+R1))Vs and between R4 and R5 similarly. And I'm not sure how to continue on. Any help...
  38. TheBigDig

    Using Nodal Analysis to determine current in a resistor

    Homework Statement Homework Equations ##V = IR## ##\sum_{k = 0}^{n} I_k = 0## The Attempt at a Solution [/B] I set the bottom node as the reference node and worked from there to find the three equations for the loop. When I try to eliminate ##I_4## by using ##I_4 = I_2 - I_3## I run into...
  39. A

    What happens to a coil of wire as current is increased?

    Homework Statement Homework Equations L = (N * F_b) / I (where F_b is the magnetic flux) emf = -L * (dI/dt) The Attempt at a Solution I originally thought that the inductance would decrease since it is inversely proportional to current. But, looking at the equation for emf, that would...
  40. A

    Simple inductance question: Finding steady state current

    Homework Statement Homework Equations I = E / R_total The Attempt at a Solution I mostly just want to clarify that my thinking is correct. The solution for this problem shows that the current is split evenly between the two paths. Is that because we're assuming that the inductor has no...
  41. R

    B Are All Four GW Detectors Currently Operational for Simultaneous Observing?

    The second LIGO observational run started last year and according to Wikipedia the germany and italy based GWs detectors Geo600 and Virgo are already operational, I would like to confirm whether as of now the 4 detectors(2 from LIGO,1 GEO and 1 VIRGO) are simultaneously fully operative. I would...
  42. alfab

    The functional form for dependence of force on Current?

    I am working on a lab where we were measuring how magnetic force between two parallel conductors varies with current and the separation between the two conductors. I need to find a formula for the dependence of Force on current to create a fit line on the data in my graph that shows the relation...
  43. mfb

    I B -> s µµ decays: Current status

    Something curious is going on with these decays. LHCb gives a seminar talk Tuesday next week, a livestream will be available. Edit: See results discussed starting here I'll summarize the current status here. I tried to keep most at the advanced (I)-level, but I don't think that always worked...
  44. jlmccart03

    Find current through inductor after many time constants.

    Homework Statement In the figure, R = 1.9 kΩ and ε0 = 60 V . When the switch is closed, the current through the inductor rises to 10 mA in 30 μs . What will the current in the circuit be after many time constants? Homework Equations I = V/R or I = ε/R if current is constant which after many...
  45. Sevs evans

    Is it possible that there is a 220 volts but low current?

    I read at the power outlet,the meter detect 220 volts but the split type AC doesn't work.it happens when I used the back up generator.
  46. D

    Find output current of NMOS transistor

    Homework Statement Vtn = 0.4V W/L = 10 NMOS1 Saturation Region Drain = 2.5V Gate = 1.9V Source = 0V Vtn = 0.4V W/L = 10 NMOS2 Triode/Linear/Ohmic Region Drain = 0.5V Gate = 2.2V Source = -2.3V tox = 9um un = 250cm^2/V W/L = 10 Homework Equations Saturation: Id = Kn * (Vgs-Vt)^2/2...
  47. Addez123

    Does a wire loops' magnetic field affect it's current?

    When you run current through a circle formed wire it generates a magnetic field. Will this field affect the current in the wire that generates it? I mean if it does wouldn't the calculations for the created magnetic field be rather circular? The magnetic field depends on the current which in...
  48. G

    Does current flow back to the power plant through the ground?

    Hi. I fear I might not have understood some fundamental concepts about electric power transmission. So we have "neutral" which is brought to Earth potential. Does this mean the electrical circuit from the power plant over highly conductive aluminium cables to my home closes back to the power...
  49. S

    Charge passing through a cross section for a time varying current

    Homework Statement The current in a wire varies with time according to the equation I(t) = 6.00 A + (4.80 A/s)t, where t is in seconds. How many coulombs of charge pass a cross section of the wire in the time period between t = 0.00 s and 3.00 s Homework Equations I=dq/dt The Attempt at a...
  50. D

    Simple test using current values to prove polarity

    I work in a large electrical machine shop. We have a test that no one can explain to me. We energise a dc field frame (in this case 6 pole) with ac and record the current draw, then reverse the polarity of connection, energise and compare values. If a pole is reversed polarity then a difference...
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