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. stevencarlover

    Induced Current Problem from the professor not in our textbook

    Homework Statement A long straight solenoid of cross-sectional area 400 cm^2 is wound with 10 turns of wire per centimeter, and the winding carry a current in the direction shown (downward). A small ring of radius 5.00 cm and resistance 0.300 ohms is placed at the center of the solenoid. If the...
  2. kd2amc

    Why is the current through I2 constant?

    Homework Statement I was going through this PDF to review for my AP Physics C E&M exam: https://apcentral.collegeboard.org/...course=ap-physics-c-electricity-and-magnetism I was also watching this video (which discusses the solutions): I am stuck on part 2(b) (page 7 of the PDF, 17:18...
  3. F

    The relationship between initial and final current density

    Homework Statement Homework Equations ##J=\frac{I}{A}## A=π r2 The Attempt at a Solution Since I is constant and the diameter is doubled , A2 = π (##\frac{2D}{2}##)2 A2 = 4 A1 J2 = I/(4A1) = J1 /4 → (E) Is my answer correct ?
  4. S

    How Do I Calculate Induced Voltage in Parallel Conductors?

    Say I have two parallel conductors that are both L long and d distance apart (center to center). I run AC power of frequency f and RMS voltage V through one conductor. That current will create a fluctuating magnetic field which will pass through the the other conductor and generate a voltage...
  5. D

    Fleming's left and right hand rule - how do they work?

    Homework Statement AC production and relationships that determine movement and current flow direction from Flaming's left hand and right hand rule. Homework EquationsThe Attempt at a Solution Left hand rule for motors- right hand rule for generators The thumb, index and midle fingers are all...
  6. J

    Current flowing in the middle branch -- Why 2 different answers?

    Homework Statement Homework EquationsThe Attempt at a Solution The two batteries are in series in both the left and right branch .This means the potential difference applied across the two middle resistors is 20 V .Hence the current flowing through them is 20/10= 2 A . This is indeed the...
  7. fluidistic

    I Do electrons have a net motion when a DC voltage is applied?

    I am wondering whether electrons have a net motion against an applied constant electric field in a conductor. Intuition tells me that "of course they should", but so far the math has shown me otherwise. Here are my current thoughts: 1) I cannot rely on the obsolute Drude's model. What's more...
  8. D

    Calculating current with and without internal resistance

    Homework Statement Calculate the magnitudes and directions of the currents in each of the 3 resistors in the circuit above, if... (a) ...both batteries have zero internal resistance. (b) ...each battery has an internal resistance of 1.0 Ω. Homework Equations I1 = I2 + I3 (Node Law)The...
  9. D

    Calculating current in five resistor/two battery circuit

    Homework Statement The circuit above has five resistors. Calculate the current through each. Homework Equations I1 = I2 + I3 (Node Law) ∑Vi = 0 (Loop Law) The Attempt at a Solution I tried to equate the currents using the node law, with I3 = I1+I2+I4+I5 But I see a flaw here, because the...
  10. P

    Current Carrying Wires: How Ampere's Law Affects Safety

    Why don't wires in any circuit touch each other and get short circuited? If two current carrying wires carry charges in same direction then from ampere's law,can't they touch each other due to attractive forces?
  11. D

    AC production production -- I need to describe how it works

    Homework Statement provide a detailed review on how alternating current is produced and the relation that determins movement and current flow direction. Homework EquationsThe Attempt at a Solution I know the basics of how AC is produced- AC is produced from an alternater (type of generator)...
  12. R

    What is the maximum value of the current through the inductor?

    1. Homework Statement : Two identical uncharged capacitors A and B each of capacitance C and an inductor L are arranged as shown in the adjacent figure. At t=0, the switch S1 is closed while switch S2 remains open.At time t=to=√(LC)Π/2, switch S2 is closed and S1 is opened. After switch S2 is...
  13. mertcan

    An interesting question about the divergence of a current density

    Hi, maybe as you know ##\nabla. J = -\frac {\partial p} {\partial t}## where J is current density p is charge density. But also we know current density flux outward the circuit is 0 because current density does not flow out of circuit an this actually volume integral of ##\nabla. J## is zero (...
  14. F

    Saturation voltage for photoelectric current

    Hi, I was wondering about saturation current in the photoelectric effect. It is clear to me that for a sufficiently large accelerating potential all of the electrons are gathered by the collecting electrode. Since it is all of them, there cannot be more, and the current won't change if the...
  15. Z

    Current through parallel cells with unequal EMFs

    1 Two cells are connected in parallel by joining the terminals together so that they both face in the same direction. One of the cells has emf 6.0 V and internal resistance 3.0 Ω, and the other cell has emf 4.0 V and internal resistance 2.0 Ω. An 8.0 Ω resistor is connected between the...
  16. J

    Using Kirchoff's Loop Rule to Determine Currents in a Circuit

    Homework Statement Homework Equations Kirchoff's Rule The sum of all V = 0 The Attempt at a Solution [/B] I think I'm having a problem determining the current at r_2 and R_3. I had originally thought the currents at both resistors would be I_3, writing E_2 — r_2 I_3 — R_3 I_3 — I_1 R_1 = 0...
  17. Gyro de Pyro

    Magnetic plate eddy current braking effect on a copper disc

    Hi, I've seen many videos of neodymium magnets sliding slowly down an inclined copper plate, or slowly down a copper tube - due to eddy current braking,but never the other way around. My question is; will a copper disc sliding down an inclined magnetic plate, or down a magnetic tube act in the...
  18. H

    Find the transient current in this circuit

    Homework Statement Homework EquationsThe Attempt at a Solution I often do circuit. But still there is always stuff i don't get.. I was asked to find 1) I1 I2 I3 immidiately after S closed 2) I1 I2 I3 after sufficient of time 3) I1 I2 I3 immidiately after S opened Just give me clue please...
  19. S

    Resistance, current and current density

    Homework Statement A coaxial cable consists of a core cylindrical wire and a coaxial cylindrical shell, as illustrated in the Figure below. Consider a cable made of copper, which has resistivity of ρ=1.70×10−8Ω·m. Thecorewirehasaradiusof r =1.0mm. Theinnerradiusofthe 1 outer shell is r = 5.0...
  20. 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...
  21. 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...
  22. Jamie_Pi

    Is There a Displacement Current in a Wire with Increasing Current?

    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...
  23. 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?
  24. 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...
  25. 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.
  26. OldWorldBlues

    Why Use Voltage Dividers Instead of a Single Resistor?

    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...
  27. 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...
  28. 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...
  29. 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...
  30. 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...
  31. 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...
  32. 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...
  33. 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...
  34. 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...
  35. 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...
  36. 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?
  37. 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?
  38. 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 ?
  39. 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 =...
  40. 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...
  41. 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?
  42. 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...
  43. 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
  44. 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...
  45. 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.
  46. 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...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
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