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. B

    In which direction does the current flow?

    Homework Statement We bind two batteries with voltage 2V and 1.7V with inner resistance 0.2Ω and 0.1Ω in parallel series in such way that we bind each positive poles and negative poles together. What current runs trough the circle? What is the voltage between contact points of the batteries...
  2. Muhammad Danish

    Calculating Current in Primary Coil: Where Does P = V^2/R Formula Come In?

    Homework Statement Homework Equations How will we calculate the current in primary coil? The Attempt at a Solution The current in the secondary coil will be 2 Amperes by I = V/R. So in the primary coil by using ratio proportion method, the current in the primary coil will be 5 Amperes. But...
  3. Jamie_Pi

    Displacement Current in a wire

    Homework Statement A wire with conductivity σ carries current I. The current is increasing at the rate dI/dt. Show that there is a displacement current in the wire equal to e0/σ⋅dI/dt Homework Equations Id = e0⋅dφ/dt dφ/dt = dE/dt ⋅ A (This is usually true, I'm not sure if it's useful in...
  4. S

    Current & Ohm's Law: Continuous vs Discrete?

    When we talk about current and ohm’s law, do we pretend that current is continuous rather than discrete in the same way that we do with charge distributions?
  5. Muhammad Danish

    Current Dividing in an Electrical Circuit

    A circuit contains a 7.5V d.c power supply and three resistors. The total resistance of the circuit is 30 ohms. Why will the largest current in the 18 ohm resistor? As far as I know is that the smallest current will be in 60 ohm resistor because it has the maximum resistance. Please explain...
  6. N

    I Drift velocity in P-N Junctions

    When a P-N junction is in reverse bias, the drift velocity of the system increases, so why is there no current flow? Is the drift velocity not connected to the current? Thanks in advance.
  7. OldWorldBlues

    Understanding voltage dividers

    Hi! I'm working on a project in which a small microcontroller with a max. analog input of 5v takes readings from multiple sensors. I would like to make this input window a bit more versatile, and turned to voltage dividers as a solution. 'Problem is, I'm having a bit of trouble understanding how...
  8. Zam0la

    If the AC EMF is 0 at t=0, then how does current pass through a capacitor?

    Hi, I have a problem understanding the ac capacitive circuit, where Vc = Vm * sin(ωt), and, current leads the voltage, so at t = 0, v = 0 which means no emf, no pushing energy for the electrons, I think, then how current is max? what is the energy source that supplied the electrons with the...
  9. K

    Determining the B-field in center of current carrying loop

    Homework Statement Determine the B-field inside the middle of a circular loop of current. Homework Equations Attempt at using Ampere's law: ##\oint \vec{B} \cdot d \vec{l} = \mu_0 i## The Attempt at a Solution ##\oint B \cdot R d \theta = \mu_0 i \Rightarrow BR(2 \pi) = \mu_0 i \Rightarrow B...
  10. S

    Force from a Current in an Infinite Wire on a Square Wire Loop Nearby

    Homework Statement Figure 6.47 shows a horizontal infinite straight wire with current I1 pointing into the page, passing a height z above a square horizontal loop with side length l and current I2. Two of the sides of the square are parallel to the wire. As with a circular ring, this square...
  11. V

    Vector potential of a plate with a uniform, time-harmonic current density

    Hi all, i tried to do this question but got stuck on the last point . Can anyone help me please? The general form of vector potential: I got the answer for A1 vector potential but don't know what assumptions i need to get the expression for the A2. Does anyone know how one can derive it...
  12. P

    Would cryodesalination be cheaper than current methods?

    Hey everyone, So I came across a company which is working on desalinating water by freezing it and was wondering what everyone here thought about it: http://cryodesalination.com/ A similar project was also being done by students of UC San Diego...
  13. amjad-sh

    A How Does Spin-Dependent Chemical Potential Generate a Spin Current?

    Hello In a paper I am working we have a two metal connected to each other, Within the ballistic approximation we adopt the Landauer approach and generate a pure spin current by applying a spin bias that is modeled as difference of spin-dependent chemical potentials across the interface. Can...
  14. B

    Computing Alternator Back EMF as a function of load current

    I am attempting to make a basic model of an alternator and determine terminal voltage levels at several different current levels. The alternator design looks like this: 900 RPM fixed, 60hz, single phase 2000 gauss permanent magnet Flux Density, Magnet circumferential velocity 9.58 m/sec, 4...
  15. F

    Current in Series Circuit: .5A Charge Flow?

    If we measure the voltage in a simple series circuit to be 5v and the resistance to be 10 ohms. The current given is .5A. Is this the amount of chage traveling from the first point to the second point per unit time, or is it the amount of charge flowing through a cross section of the conductor...
  16. A

    Average power dissipation for induced current

    Homework Statement A wire shaped as a semi-circle of radius a rotates about the axis OO’ with a constant angular velocity ω in a uniform magnetic field with induction B (attached figure). The plane of the rectangular loop is perpendicular to the magnetic field direction. The total resistance of...
  17. F

    Meaning of Current in Ohm's law

    If we had a parallel circuit with a voltage of V between the beginning and end, and the circuit has a resistance R, then the current given by ohms law is I = V/R. What does this mean? The current is not the same throughout the whole circuit. Where is the current equal to this value?
  18. F

    Does Ohm's Law Apply to a Circuit with Current but No Voltage?

    in a circuit like the one in the attached picture, the voltage between two points in between two resistors should be 0. But there is current flowing through the circuit. So what’s going on here? Does ohms law not apply in this situation for some reason?
  19. J

    Analyzing Current in a Branch: Using KCL and KVL

    Homework Statement Q . Find current i through the 5Ω resistor ? Homework EquationsThe Attempt at a Solution I would like to understand what does leftmost 1A represent . I haven't seen something like that before in my book . Is it a Galvanometer or something else ?
  20. R

    Finding the maximum value of current through the inductor

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] I got the first 2 parts, but I'm having trouble with the last one. For the time the switch S1 is closed, I derived ##q(t) = CE(1 - \cos(\frac{t}{\sqrt{LC}}))##, by writing the loop equation ##\frac{E}{L} - \frac{1}{LC}q =...
  21. H

    Magnetic field at the center of 3 wires carrying current?

    Homework Statement each wire carrying 10 Amps a = 0.3 meter point o located in the center Homework Equations B = permeability constant * I / ( 2 ##\pi## r) r = distance between O and the wire r perpendicular to B and I A = carrying current into the page B and C = out of the pages The...
  22. M

    Why no induced current when these coils are stationary?

    These is there no induced current when the coils are stationary relative to each other? Isn't there still current (moving charges) in the the one on the left to cause a current in the one on the right when neither coil is moving?
  23. J

    Does the current increase or decrease through the resistor ?

    Homework Statement Homework EquationsThe Attempt at a Solution This looks to be a simple problem but the answer key has left me wondering whether I am thinking correctly . I get option 1) whereas answer key states option 3) . Since the variable resistance R increases , the resistance...
  24. D

    How Does W=VIt Describe Energy in Electrical Circuits?

    Homework Statement I have to explain the equation W=VIt and apply it to a circuit. But I do not undertsand what the equation shows. Homework Equations W=VIt The Attempt at a Solution My rough guess is : work done is equal to the time (t) taken for 1A of current to flow at 1V
  25. F

    Find the current using Nodal Analysis

    Homework Statement Find i using Nodal Analysis. Homework Equations V = I * R The Attempt at a Solution solve (1) , (2) , and (3) to find V1 , V2 ,and V3 V1 = 50/3 = 16.67 V V2 = 80/3 = 26.67 V V3 = 40 V 40 - 80/3 = 5i i = 2.667 A However , the correct answer is 1.522 A .. I don't know...
  26. O

    MHB Describing the resulting current

    Suppose that the current flowing in an electric circuit is the sum (superposition) of two alternating currents, one given by I1 = 2 cos t and the other given by I2 = −2 sin t at time t. Carefully describe the resulting current in the circuit.
  27. mheruian

    Understand the Current Consumption of an IC in its Datasheet

    << Mentor Note -- Thread moved to the EE forum >> Hi, I'm new here and maybe this is the best section where I could need help :) I've been interested in electronics lately (not schooling anymore, more on self-study, but I'm not that smart, just a dedicated one and i can't understand everything...
  28. C

    Understanding Current Flow in a Circuit with a Current Source

    Homework Statement Say I have the following hypotehtical circuit, Ignore the open circuit at the bottom. Would I be correct in saying that all of the input current i goes to the resistor R or would it be split? Because I know for a current source that it has to produce that current i5 no...
  29. D

    What Does the 10% Resistance Boundary Mean in Circuit Measurements?

    Homework Statement if someone could help me with this it would be much appreciated. In physics, I used a 98Ω resistor in a series circuit and measured the current and voltage output from battery, using the current and voltage I calculated the resistance. I=0.0094A V=1 Rt=1/0.0094=106.38Ω even...
  30. J

    Induced current in two connected loops

    Homework Statement Homework EquationsThe Attempt at a Solution Call the middle point where the two loops meet O . The induced EMF in the right wire should be anticlockwise and in the left loop should be clockwise . But there can be only one current in the wire . The induced EMF in the...
  31. J

    How Accurately Can Induced EMF Represent Batteries in Circuit Problems?

    Homework Statement Homework EquationsThe Attempt at a Solution Sorry for the unclear image . EMF induced in the left loop = 8 Total Resistance of the left loop = 6 Ohms Current will be induced in anticlockwise direction in the left loop of magnitude 4/3A. EMF induced in the right...
  32. J

    What is the current induced in the loop when the area is π(b2 - a2)?

    Homework Statement Homework EquationsThe Attempt at a Solution The area of the loop is π(b2 - a2) Emf induced E = Rate of change of flux = πk(b2 - a2) Resistance of the wire R = 2πλ(a+b) Current in the loop = E/R = [k(b2 - a2)]/[2λ(a+b)] . This doesn't matches with the given answer .
  33. rocky4920

    Finding the magnitude of the current flowing through a wire

    Homework Statement Homework Equations The Attempt at a Solution [/B] My question: in order to find the answer for part d, I have the L, the B, and the mass. However, the F equations have I, which I do not have. Would I have to solve for I in order to find F? If so, I would like some...
  34. TheBigDig

    Find the time dependent magnetic field intensity

    Homework Statement Calculate the time-dependent magnetic field intensity B(t) at an axial distance r from a long, thin straight copper wire that carries a sinusoidal current with an alternating frequency of 50 Hz and a maximum amplitude of 0.5 A. Homework Equations I = Asin(\omega t) B =...
  35. H

    How to find the power consumed by the light bulb

    Homework Statement (Is the image read-able now? ) The fig 1 shows the relationship between voltage and current when voltage is applied to a certain light bulb. Next, in fig 2, the bulb is connected in series with a 12-V battery and a 5 ohm resistor. Question : what is the amount of power...
  36. S

    Radiation from an infinite current sheet

    The Feynman LECTURES ON PHYSICS (NEW MILLENNIUM EDITION) by FEYNMAN•LEIGHTON•SANDS VOLUME II discusses radiation from an infinite sheet of switched-on constant current in section "18-4 A traveling field" on page 18-15. The solution shows a constant E field and constant B field at a given point...
  37. tensor0910

    Engineering Determine the current in this circuit

    Homework Statement Find the current Ig[/B] Homework Equations [/B] V1 = R1/(R1 + R2) * Vs 1/Rtotal = 1/R1 + 1/R2 + 1/R3...exampleThe Attempt at a Solution I know what I did wrong, but I don't know how to avoid it. Here's what I mean. How do you know which way its suppose to be?
  38. D

    Why is my calculated resistance higher than the resistor used

    Homework Statement Why is my calculated total resistance of the circuit higher than the resistor used in series and the theoretical total resistance? In a series circuit I used a 100Ω resistor and measured the current at 1.0v intervals from 1.0-5.0v. At 1.0v the current was 8.70mA using a 100Ω...
  39. M

    Force between Parallel Current Carrying Wires

    Homework Statement Two parallel wires have currents that have the same direction, but differing magnitude. The current in wire A is I, and the current in wire B is 2I. Which one of the following statements concerning the situation is true? A) Both wires attract each other with the same force...
  40. H

    Find the current induced in a wire loop by a nearby current

    Homework Statement Homework EquationsThe Attempt at a Solution When the circuit moves creates magnetic force that moves the some charges in the wire and that is a current. That is what i thought. F = Q.v B sin theta B = ( permeability Of vacuum* I)/(2pi.r) But how to find the I? Thank you...
  41. P

    Electric field due to current carrying conductor

    Does static charge near to a constant current carrying conductor experience force on it? I am asking this question because i have learned that electric field and mangnetic field are same thing but viewing differently with respect to the frame of reference...when a positive test charge moves (...
  42. E

    B Current values for Friedman's scalar and its derivative?

    What are the current values for Friedman's scalar and its first derivative with respect to time? Thanks.
  43. C

    What is the direction of the current in the given image?

    Homework Statement In the picture 20.40, what is the direction of the current induced in the resistor at the instant the switch is closed.[/B]Homework Equations Right hand rules- Point thumb in direction of current and your fingers will curl in direction of magnetic field. Lenz's law. The...
  44. T

    Calculate magnetic potential of a given current density

    Hello, I'm current studying magnetostatics and I'm struggling to understand the equation for A. Here is the equation from Griffith in the attachment. My confusion is, if the object is a cylinder and the current density is a function of s, J(s), then how would I write r-r'? Thank you!
  45. W

    The magnetic flux density at point P between parallel wires

    Homework Statement In the picture at points A and B are two thin parallel wires, where traveling currents are 15 A and 32 A to opposite directions. The distance between wires is 5.3 cm. Point's P distances from A and B are the same. Calculate the magnetic flux density at point P. Homework...
  46. M

    Confused about choosing current direction in nodal analysis

    Homework Statement The problem states: Determine the voltage labeled v in the following circuit: https://ibb.co/hz0Q37 The variable is the voltage across the 2 ohm resistor. The ground I chose for this example is located in the center of the circuit. Homework Equations V=IR I guess. The...
  47. M

    Current in circuit with many resistors

    Homework Statement Find the current and potential difference through 3Ω resistor. Homework Equations ε - I1 (Ω) - I2 (Ω) ... = 0 The Attempt at a Solution I only got as far as finding the equation: ε - I1 (3Ω) - I2 (16Ω) = 0 (For complete loop around circuit) I know I have to find I1, but I...
  48. Biker

    Magnetic force on a current carrying wire

    I was wondering what would happen if you have a current carrying wire that makes an angle with the magnetic field and how to describe its motion. Prepare yourself for the bad drawing. I will first show how the method I used works for a simpler case where Magnetic field and current are...
  49. H

    Infinite wire -- Magnetic field from a current in a long L-shaped wire

    Homework Statement A long wire with a current changes direction by 90 degrees. Calculate the magnetic field at the point at a perpendicular distance of S from the wire before it changed direction and a distance of T from the segment of the wire after it changed direction. Homework Equations I...
  50. T

    Hall Effect in an alternating current circuit

    Since the classical Hall EMF is proportional to current, in an alternating current circuit, the Hall Emf should also follow an alternating pattern. Is it so? Or the Hall Emf doesn't change in a sine wave pattern instead remains more or less same and has a voltage based on the average/rms...
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