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. T

    Current at Resistor 2: How to Calculate using Capacitor Voltage and Ohm's Law

    Homework Statement In Fig. 27-66, R1= 10.0 kΩ, R2 = 15.0 kΩ, C = 0.400 µF, and the ideal battery has emf E = 20.0 V. First, the switch is closed a long time so that the steady state is reached. Then the switch is opened at time t = 0. What is the current in resistor 2 at t = 4.00 ms? This is...
  2. reddvoid

    Energy consumed in a digital circuit

    I have a digital circuit , to find the energy consumed by the circuit, I am monitoring the current drawn from the supply and integrating it to get the charge pumped into the circuit ... and the total charge*V supposed to give me total energy consumed by the circuit. But I am getting a small...
  3. bob012345

    Dynamics of Lorentz force on a current carrying wire

    Hello all, I've been pondering a problem with a current carrying wire in a magnetic field. The Lorentz force is easy, ILB, with a velocity 90 degrees to the B field. So let the force accelerate the wire. Assume only one segment of the wire that has current in one direction, say up, is in the...
  4. T

    Calculating Torque and Current for Quadcopter Rotor Blades

    Homework Statement The rotor blades of a quadcopter are 10cm long. Given that the thrust force generated by each rotor is 1N (giving a total of 4N for 4 rotors), calculate the torque () on each rotor, and the current drawn (I) from a 10V battery, given the following: Density of air, a = 1...
  5. astrocytosis

    Induced current in a loop of wire when straight wire is cut

    Homework Statement A square loop, side a, resistance R, lies a distance s from an infinite straight wire that carries current I (pointing to the right). Now someone cuts the wire, so I drops to zero. In what direction does the induced current in the square loop flow, and what total charge...
  6. Drakkith

    Engineering Finding Current in a Parallel RLC Circuit

    Homework Statement Find io for t≥0. Express your answer in terms of t, where t is in milliseconds. There is no energy stored in the circuit in (Figure 1) when the switch is closed at t = 0. Homework Equations ##x(t)=x_f+[B_1cos(ω_dt)+B_2sin(ω_dt)]e^{-αt}## The Attempt at a Solution Let...
  7. kmm

    Magnetic field of a cylinder with current down the center

    I was just in a conversation with someone regarding the magnetic field resulting outside of a solid cylinder, with a current moving down the center of the cylinder, and then the resulting magnetic field after removing the current. Now I haven't thought about magnetic fields/magnets for a while...
  8. Drakkith

    Engineering Current Through a Capacitor in a RC Circuit

    Homework Statement Find ##i(0^+) ## and ##i(t), t≥0^+## Homework EquationsThe Attempt at a Solution [/B] I'm having trouble finding the current through this capacitor. I tried using a KVL loop for ##t=0^+##, but I'm doing it incorrectly or something. Earlier in the problem I found...
  9. G

    Getting negative current on Zener Voltage Reg Circuit

    i've built a bridge rectifier with a Zener Voltage regulator. 12V peak secondary 3300uF Capacitor 1k ohm load 1k ohm series resistor for the zener and a 1n4728A Zener diode. i'm getting a 2.8V steady voltage, but when i measured the current going through the load with my DMM it's measuring...
  10. Z

    The origin of self inductance in a current loop?

    Hi Forum I am trying to get a better grasp of the relation between electric field and the magnetic field. The overall question is "What is The origin of selfinductance in a current loop?" Here are my thourghts: A battery is connected to a say circular wire with some resistance. The current...
  11. Cocoleia

    Current and power with transformers

    Homework Statement I am working on the following problem: And ideal single phase transformer 240V/2880V is supplied with a 240V source via a resistance cable of 3ohm. If we connect a R=720ohm resistance to this, determine the primary current and the dissipated power in R. (I'm sorry if some...
  12. R

    Using Kirchoff's Voltage Rule to find currents in a system

    Homework Statement Then solve these equations for i1-4 Homework Equations V=IR The Attempt at a Solution 80i_1-50i_2-30i_3 = -120 -50i_1+100i_2-10i_3-25i_4 = 0. -30i_1-10i_2+65i_3-20i_4 = 0. -25i_2-20i_3+100i_4 = 0. i_1=-4.18239492 i_2=-2.66455194 i_3=-2.71213323 i_4=-1.20856463...
  13. D

    Peskin complex scalar field current

    Homework Statement i'm trying to calculate the charge operator for a complex scalar field. I've got the overal problem right but I'm confused about this: On page 18 of Peskin, it is written that the conserved current of a complex scalar field, associated with the transformation ##\phi...
  14. G

    How do you find the current going through a weird circuit?

    Homework Statement Homework Equations at point C: i2 - i3 - i4 i2 = i3 + i4[/B] The Attempt at a Solution I labeled all the currents going through each resistor in the picture[/B] for loop ABC: 2000i1 = 3000i2 + 4000i3 for loop BDC: 3000i5 = 2000i4 + 4000i3 at point C: i2 - i3 - i4 i2...
  15. M

    Question about circuits with transistors (current, voltage)

    Homework Statement 1. In Figure A-1 of Experiment 18, assume that Vdc = 8Volts, R1 = 1kOhms, R3 = 7kOhms and there is no R2 resistor. Determine the current in R1 when the transistor is fully on and carrying current. Express your answer in mA. 2. In the circuit of Figure A-1, Experiment 18...
  16. C

    I Electrical Current Repelling Magnets Due to Relativity

    I recently watched this Varitasium video where he explains the magnetic field due to a current carrying wire. In the video he explains how what we see and describe as the magnetic field produced by a current carrying wire is actually just a electric force caused by the an imbalance of charges...
  17. astrocytosis

    Magnetic field above the center of a square current loop

    Homework Statement Find the exact magnetic field a distance z above the center of a square loop of side w, carrying a current I. Verify that it reduces to the field of a dipole, with the appropriate dipole moment, when z >> w. Homework Equations (1) dB = μ0I/4πr2 dl × rhat (2) r =...
  18. D

    BLDC motor as generator to power eddy current brakes

    Hi everyone - here's a concept that I'd like a few opinions on: As part of a project, I'm looking at using a brushless DC motor mounted on a high-speed vehicle as a generator. Once the vehicle hits its top speed, the batteries should disconnect from the motor and the vehicle's own velocity will...
  19. Cocoleia

    Phase and Line current in 3 phase circuits

    Homework Statement I need to first find phase current in the load and line current from the supply Homework EquationsThe Attempt at a Solution I thought it would be easier to work with a star because then the Ztl would be in series with it... I am not sure how to find the current but my best...
  20. astrocytosis

    Radial force on charged particle in beam of positive ions

    Homework Statement Many experiments in physics call for a beam of charged particles. The stability and “optics” of charged-particle beams are influenced by the electric and magnetic forces that the individual charged particles in the beam exert on one another. Consider a beam of positively...
  21. M

    Solenoid with current carrying wire inside

    Homework Statement I have a solenoid with a wire carrying current in the center. The wire has a radius of a, the solenoid has a radius of b. I need to find the magnetic field inside of each region. Inside of the wire, mu =/= muo. Homework Equations Wire B field = uo I/2*pi*r Solenoid B field...
  22. R

    What Happens to the Current Through an Inductor When the Switch Opens?

    Homework Statement "The switch in the circuit in the figure has been closed for a long time and is opened at t = 0. Find i(50 ms)." I attached an image of the circuit below.Homework Equations KVL: Ri + q(t)/C - q(0)/C + vc(t) + Li' = vs(t) Li'' + Ri' + i/C = vs'(t) Where vc is voltage across...
  23. N

    Nodal analysis- Current directions for KCL

    In node analysis, after labeling the nodes. I don't know how to choose currents direction to apply KCL. it seems too complicated.. and I end up every time getting different answers the the solution sheet. I've an exam tomorrow. would be much appreciated if you could help me better understand the...
  24. J

    Step-Up Current Via Transformer

    I'm a mechanical engineer by trade, but I am working on developing a testing apparatus that oscillates a neodymium magnet between two solenoids offset by by a 180 degree phase shift. Basically, one solenoid pushes, the other pulls. To get this, current is essential. I need each solenoid to get a...
  25. N

    Engineering Use Circuit reduction, voltage and current divider to find i

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > in the solution sheet, He took the 18 ohms parallel with the 9 ohms and not the 6 ohms. I don't understand why he took this approach. I was going to take 18 ohms parallel with the 6 ohms and find...
  26. B

    Determine a cable core diameter for RF current carrying loop

    Basic Question Alert ! (I need to brush up my basics and need your help) Problem Statement: I wish to make a current carring cable loop to generate a controlled magnetic field. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html As I understand, the magnetic field generated depends...
  27. Cool4Kat

    How much current does a cell phone use?

    I am doing a series of videos on the history of electricity and I am working on a video on Volta and the first battery. Anyway, I want to compare the voltaic pile to a typical li-ion battery running my iPhone. Now the voltaic pile could easily create 20 V of potential but it had high...
  28. G

    How to calculate the current in a 400 nm wire of graphene

    Hi, I need to calculate the current in a 400nm piece of graphene. Can some one help me please? I found online that graphene has electron mobility of 200,000 cm^2/( V s). My best attempt is as follows. Using the equation vd = uE where E is the magnitude of the electric field applied to a...
  29. E

    Checking my answer.... finding the power of a current and a voltage source

    Homework Statement The current source and voltage source in the circuit shown in the Figure below are connected in parallel so that they both have the same voltage, vs. The current source and voltage source are also connected in series so that they both have the same current, is. Suppose that...
  30. K

    Why you can't measure voltage and current at the same time?

    In my physics textbook it says that ammeter in circuit C shows higher current than ammeter in circuit A and D. And the voltmeter shows higher voltage in D than in B, and C. It's explained in the book that way: some electric current is passing through the voltmeter in C, thus the ammeter will...
  31. E

    Dark current and dark count in photon collection devices

    Does anyone know of a simple relation between dark current and dark count in photon collection devices?
  32. mktsgm

    Electrical current question -- electrons moving through wires....

    I have a silly question. In a simple electrical circuit, we know that the two ends of the wire are connected to different potentials of a battery through the load. Potential difference causes the current flow. But how the wire comes to know that the other end of it, is connected to different...
  33. T

    How does a resistor exactly reduce current flow in a circuit

    Greeting . It is clear to me that the resistor represents a physical obstruction to the passing current I do not know how exactly it works and I will try to show what I was really interested in the diagram.
  34. P

    Calculating Resistance in a Circuit using Kirchhoff's Laws

    Homework Statement 1) what is the total resistance of this circuit between points A and B? 2) if the horizontal resistor was replaced with an ammeter what would it read if a 6V battery was placed between points A and B? let R = 20 ohms Homework Equations The Attempt at a Solution had...
  35. N

    Calculating Current in a Wire Loop Inside and Outside a Solenoid

    Homework Statement A 2400-turn solenoid is 2.4 m long and 10 cm in diameter. The solenoid current is increasing at 1.4 kA/s . Find the current in a 5.0-cm-diameter wire loop with resistance 9.0 Ω lying inside the solenoid and perpendicular to the solenoid axis. Repeat for a similarly oriented...
  36. Philosophaie

    Current Density and Charge Density in a loop of Wire

    I am trying to formulate the Current Density for a Loop of wire with a diameter,d, current,I, and an cross-sectional Area of the wire ##\pi(d/2)^2##. With spherical coordinates (radial, azimuthal, polar) ##\bar j## = ##\frac{I}{\pi(d/2)^2}*cos \theta *sin \phi \hat x##...
  37. T

    Magnetic flux and inductance?

    If a current flows in a straight wire, a certain amount of magnetic flux will be generated around it. Now suppose I put an iron tube around the wire (but don't change the current). I know the inductance will increase, but is that because more total flux is now being generated, or is the total...
  38. G

    Arbitrary current with mesh analysis

    Given the circuit in the diagram I was wondering would I be able to make ib equal to the mesh i3. I have the equation for my Super Mesh at i1 and i3 which is: -25+30i3+5Va+20(i3-i2)+10(i1-i2)=0 (1). The mesh i2 is equal to -2A (2). subbing (2) into (1) gives: -25+50i3+5Va-30i2+10i1=0 (3)...
  39. sams

    A Difference between conduction & convection current density?

    Hello Everyone, Could anyone please explain the difference between the conduction current density (J=σE) and the convection current density (J=ρvd)? I really appreciate any examples or applications to further elaborate these two theories. Note: vd is the particles' average drift velocity...
  40. Cocoleia

    Analyzing a Current Mirror: Finding Rref for Vcc=8V and Icopy=0.38mA

    Homework Statement I am working on this problem. They start out by giving me: I am asked to find Rref such that Vcc=8V and Icopy=0.38mA. Homework Equations Transistor equations The Attempt at a Solution In this case, they never specify if IB=0A (sometimes it does ?) but I would assume that...
  41. T

    Is current proportional to emf

    Faraday's law states that emf is proportional to change in flux. The scenario I am using is a magnet is moved towards a closed loop. As it moves towards the loop, flux through the loop is increased causing a emf to be induced. Does I also know that a current is induced. So does that mean current...
  42. T

    Current in secondary coil as current in primary increases

    Hi, so the scenario is that the primary coil of a transformer is attached to a battery in a circuit with a variable resistor. The resistor is set to the maximum resistance. As I increase the current in primary coil by reducing resistance at a constant rate, will the current in the secondary...
  43. Philosophaie

    Scalar Potentials and Electromagnetic Current

    For a Dipole and a Torad (or a Solenoid) I need to find the scalar Potential,phi, Charge Density,rho, and then 4-Electromagnetic Current,J(rho*c,j) where A and J are 4-vectors and a and j are 3-vectors. -grad^2(phi) + 1/c^2*d/dt(phi) = rho/epsillon0 where grad(A(phi/c,a)) = -1/c^2*d/dt(phi)...
  44. B

    Current, voltage : brightness of bulb in parallel or series

    Hello I'm working through a book (with answers) but am struggling with voltage, current, resistance and circuits. Please check my understanding below and let me know if I've finally understood. Thank you. In particular I'm confused in Q2 Q1. A student connects light bulbs, A and B, and...
  45. M

    Question about Capacitance and Inductance

    Homework Statement [/B] Hey everyone, I recently got two problems on capacitance and inductance and need some help on them. Here are the two problems: 1. A Royal Red Robin Burger contains 1230 food calories. Also, more that the daily requirement for protein, fat, sodium ..., even without fries...
  46. S

    The use of current transformers

    Hello everyone, Recently, i have designed a capacitor bank for a company which they already have their main switch board with metering stuff. The ammeter of the main switch board has its own CTs but for the capacitor bank I need to install a CT separately. The spec of existing CTs for main...
  47. T

    What is current return path in 230V European single phase

    My question is :what is the role of neutral conductor in the 230v European single-phase system .My assumption how it works that a neutral conductor serves to close the circuit between phases and to carry the imbalance current between different phases If all the phases are balanced then the...
  48. Jhon Paul

    How to Configure a Power System for High Current and Low Voltage Demands?

    I have to configure a power system for a furnace which demands very high current of the order of 50KAmps with low voltage of the order of 100 volts. Can anyone help me to get insight into how to configure the power system in boarder way. I am planning to use a transformer with thyristors .
  49. JoeMarsh2017

    Finding Turns Ratio and Average Current in the Primary Winding

    Homework Statement A half wave rectifier circuit has a transformer inserted between the source and the remainder of the circuit. The source is 240Vrms and 60 Hz, and the load resistance is 20ohms. 1) Determine the required Turns Ratio of the transformer such that the average load current is...
  50. Esfand Yar Ali

    Piezoelectric transducer current

    How can I increase the output current from a piezoelectric trasnducer using PZT ceramic? The requirement is about 1.2 Amp but currently I'm only getting about 0.2 mA per unit.
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