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. RodionGork

    Incandescent Bulb - suitable approximation for voltage-current curve

    Hi Friends! Regard the 2 kW electric kettle and 60 W incandescent bulb - what happens if we plug them in series? It is the problem I often ask my students somewhere at the end of the term to check if they remember basic "laws" about electricity. Recently I started collecting some exercises on a...
  2. BuggyWungos

    Magnetic Field of an infinite current-carrying wire at a point

    My attempt: $$d\vec{B}(r) = \dfrac{\mu_0}{4\pi}\dfrac{Id\vec{l}r\sin{\theta}}{r^2}$$ $$d\vec{B}(r) = \dfrac{\mu_0}{4\pi}\dfrac{Id\vec{l}\sin{\theta}}{r}$$ $$ \sin{\theta} = \dfrac{y}{(x^2+y^2)^{1/2}}$$ $$ d\vec{B}(r) = \dfrac{\mu_0}{4\pi}\dfrac{Id\vec{l}}{r}\dfrac{y}{(x^2+y^2)^{1/2}}$$...
  3. Heisenberg7

    B Magnet inside a solenoid with current

    What would happen if we tried forcing a bar magnet into a magnetic field created by a solenoid (look at the picture)? Assume that both the bar magnet and the solenoid are isolated form any other source of a magnetic field. What I am thinking: First of all, if we tried forcing the north side in...
  4. Y

    Induced currents on a pair of separated dipole antennas

    Hello, I need to calculate the expression for a current on two dipoles separated as shown in the attached full task . I need to present a solution,lets take the simplest case. Theta_in=0 I need to find the expression for the currents on the dipoles...
  5. UrbanFarmEngineer

    HVAC Electrical Issue: Current Leakage from Furnace

    Hey Everyone, I am not an electrical engineer I am a biochemmie and I am here for your help. I have been learning household wiring and troubleshooting electrical wiring problems in my house for the last few months and I am stumped on an HVAC issue and would really appreciate some insights from...
  6. ananunes06

    I Does current decrease inside a wire or does it increase it's velocity?

    I've been really confused on how electricity and circuits work 1. If eletrons "slow down" inside a resistor (or wire, I'm considering it's resistance to be ≠ 0) because of collisions with the lattice, then wouldn't the electrons pile up? The charges accumulating doesn't seem to be good. 2. Some...
  7. Sidsid

    B-field from a current in a wire above a conducting surface

    I first thought of imaging techniques, because the setup reminded me of it, but i have only ever seen those of electrostatics. If i for example add a current in the opposite direction and with the opposite heigth of the surface the fields dont cancel out at the surface, i think. What is the best...
  8. A

    Finding magnetic field using Ampere's Circuital Law

    I followed the following approach which is also the listed solution: First of all, from Ampere’s circuital law, we get: ∮B⋅dl=μ_0I Here, I is the enclosed circuit in the circular Gaussian surface of radius c and its value will be: I=J⋅πc^2 Here, J is the current flowing per unit cross-sectional...
  9. AmanWithoutAscarf

    Question about the current components inside the Corbino disk

    Problem: An annular disk consists of a sample of material with thickness d, inner radius ##\displaystyle R_{1}##, outer radius ##\displaystyle \ R_{2}##, and electrical conductivity ##\displaystyle \sigma##. Let the radial current ##I_0## flow from the inner periphery to the outer periphery of...
  10. M

    B Direction of drift velocity vs direction of current

    I've done internet searches on this. There doesn't seem to be any agreement. Is the direction of the drift velocity in a wire the same as the (conventional) current? [AI Chatbot reference deleted by the Mentors]
  11. Bling Fizikst

    Net force between two conducting strips

    I have a lot of doubts regarding this . Let's say the resistance is ##R## where the net interaction force becomes zero . So , the current flowing should be : $$i=\frac{V_{\circ}}{R}$$ Will charges be induced like in capacitors? If yes then let's say ##\pm q## is induced and the length of the...
  12. S

    Is My Answer Correct for Calculating Average Current on a Ring?

    $$I=\frac{q}{t}$$ $$=\frac{4Q}{T}$$ $$=4Qf$$ My answer is (a). Is that correct? Thanks
  13. S

    Flux linking (and de-linking?)

    Initially the current is non-zero therefore we have a magnetic field present, and at the end there is no current therefore there is no magnetic field present. When we open the switch, and the current drops to 0, there is a change in the magnetic flux of B, as the field from A has gone. This...
  14. U

    Does constant DC current in curved wire produce EM wave?

    Accelerating electric charge produce EM wave Does constant DC current in curved wire produce EM wave, because el.charge has radial acceleration in curved wire?
  15. fluidistic

    I Curl of current density

    Hello, I have derived an expression for ##\vec J## in a particular, unusual physical problem in 2D. The expression is different from ##\vec 0## everwhere in the material except at at least two different points. Can I conclude that the only way for this to occur is that ##\vec J## itself decays...
  16. G

    I Does displacement current create a magnetic field? And Lorentz force?

    Hi. Does displacement current create a magnetic field by Biot-Savart? I googled and found contradictory answers. Also, in the presence of an external magnetic field, is it meaningful to calculate a Lorentz force acting on displacement current? What does the force actually act on then?
  17. D

    B Found a circuit where current is zero across an ohmic device (dV>0)

    I know that a voltage difference doesn't necessarily imply current flow, but all the explanations I seem to find of that either say that that happens because the resistance is infinite, or there is nothing connecting the two points in question (the two are basically the same thing, as I...
  18. kma

    Medical Is 5 milliamps at 240 volts dangerous?

    Quick question, is 5 milliamps at household voltage like 240 dangerous? See many conflicting views on this, official accounts state that on an electric shock chart, 5ma is nowhere near the level needed to cause any damage but some electricians on reddit say with low body resistance even low...
  19. Kartofen69420

    Calculating Magnetic Field at Point P for Perpendicular Current-Carrying Wires

    A wire coinciding with the X-axis carries a current I1 in the direction of increasing x. A second wire is parallel to the Z-axis at a distance R, and carries a current I2 in the downward direction as indicated in the figure. The magnetic field at point P (0, 0, R) is: (options and diagram in photo)
  20. U

    Why and by how much does unbalanced current flow increase EM radation?

    In this video at 0:38 man say that unbalance current flow increase magnetic radiation far away, even few streets away from source.. 1. Why radiation increase in these situation? 2. Is every system subject to that phenomenon and when unbalanced current happend? 3. Will emf meter show this...
  21. J

    I Question about Activating Solenoids that are facing each other

    In this situation I would have two solenoids facing each other, such that both ends are north for example, and when activated they are actively experiencing repulsion, I know that the magnetic field of both would decrease in strength, but would there be any affect on the electrical input of each...
  22. lonely penguin

    I How relative is the magnetic field of a current carrying conductor?

    According to the special theory of relativity the electric and magnetic fields observed from a charge distribution should depend on the relative motion of the observer. For example consider a linear arrangement of point charges which are fixed relative to each other. An observer who is...
  23. L

    Is current flowing into a battery always equal to current flowing out?

    Image from Wiley Intro Physics Textbook sample problem This was the given problem. In the diagram, one can see that the current flowing into each battery equals the current flowing out of each battery. Is this always the case, and why? If there was only one battery, I guess it could be...
  24. Juanda

    I How Do Eddy Current Dampers Work in Space Applications?

    This post is somewhat of a continuation of this other post. I would like to better understand induction and be able to link the electrical equations with Newton's. For reference, this is a paper about the Eddy Current Damper I would like to study first. I think these components are very well...
  25. G

    Inrush current in a transformer chain

    This is the proposal, except the two middle voltages are 110V, not 12V. Say the max switch-on inrush current of XFMR1 is xA with the secondary open, would the value change significantly in the above arrangement, with the secondary of XFMR2 open?
  26. L

    Current flowing in an open circuit

    1. Consider this diagram. Does the bulb light up? The equation I=V/R tells me no, but if there is a potential difference between the two points, surely current will flow and the bulb will light? As there is nowhere for the electrons to go, I assume it will only light for a very short period of...
  27. M

    Direction of current as bar magnet moves uniformly through copper ring

    Suppose the ring is held stationary such that its area vector points upward. The magnet moves downward toward the ring at constant velocity north-pole first. (The starting position is shown in the figure.) Since ##\vec{B}## is downward while ##\vec{A}## is upward, ##\Phi_B=\vec{B}\cdot\vec{A}##...
  28. M

    B Current-carrying coil and solenoid

    What is the difference between a current-carrying coil and a solenoid?
  29. L

    B Stationary charge next to a current-carrying wire

    (1) https://www.youtube.com/results?search_query=relativity+and+electromagnetism (2) If I understand this correctly, then, well, shouldn't all current-carrying wires exhibit a small amount of positive charge?
  30. S

    Why do almost all rivers in the world flow North to South?

    I recently heard the narrator of a podcast state that the current of almost all rivers in the world flows from North to South. The narrator said the Nile River is one of very few rivers in the world that flows from South to North. I cannot figure out why almost all rivers in the world have a...
  31. Grandpa04

    Finding current of circular (toroidal) solenoid

    I assumed that the radius is referring to a major R like in the image below. I plugged all the values (except for length) into the equation B = µ*N*I/2πr to get 155.6 A for the current value. I am unsure if this is the correct value or if radius refers to minor r of solenoid, in which case a...
  32. milkism

    Complex RLC Circuit Problem (System of diff eqs)

    The following circuit is: Going clockwise the current ##I_1## goes through resistor ##R_1## and voltage ##V_11##. Current ##I_2## goes through capacitator ##C_1## and ##R_2##. Current ##I_3## goes through resistors ##R_3## and ##R_4##. Current ##I_4## goes through resistor ##R_5##, but from...
  33. C

    How Does Induced Current Change with Loop Acceleration Through a Magnetic Field?

    A wire loop accelerates from position 1 to position 5. It enters an area of a homogenous non changing magnetic field B. Rank the induced currents in the loop starting from the biggest. in solutions it says I4>I2>I1=I3=I5=0 but i dont understand why
  34. Maghraby

    Homework help : The difference between these 2 circuits

    I want to know the difference between the two circuits below , and Why don't I bundle both batteries into one 24V battery? pls help me in this . This is the original circuit: And to merge the two batteries , What is the resulting value of a battery resulting from the merger? I thought...
  35. Dario56

    I Which law defines the AC inducing voltage in the inductor?

    If we connect an inductor without ohmic resistance to the alternating voltage source, voltage should induce in the inductor because of the Faraday's law. Voltage is induced by changing magnetic flux through the inductor which is accomplished by alternating current through it. Therefore, in order...
  36. D

    Engineering Parallel/Series combination of PV modules

    The solar irradiance incident on the PV modules is 5 kwh/m^2-day.The current each module can provide is 5 A and the voltage due to the separation of charge carriers is 18 V under standard conditions (1 Sun=1000 W/m2) so we would have to connect two modules in series to exceed the voltage of the...
  37. skibidi

    What is the maximum current in a RL circuit using V=IR?

    I found the time constant using L/R and got 0.62s (3.6H/5.8ohms) I found the initial current V/R and got 4.086A (23.7V/5.8ohms) I(f) = 4.086A(1-e^(-0.5s/0.62s)) Then I plugged it into the equation and got 2.26A and it was wrong
  38. T

    I Is the magnetic field from this current rotationally symmetric?

    Imagine a very large disc with current converging to it's center as $$ I=- \frac{k}{r} \hat{r}$$ Obviously ##\theta## is absent in the equation so the magnetic field by this current should look the same no matter which angle one is observing. Then does this mean that the magnetic field is...
  39. S

    I Question: Interpretation of Current and Magnetic Field Using Relativity

    The current in a wire is said to produce a magnetic field and a force on a charge. It is said that the correct way to interpret the effect is because of relativity. So does that mean that that the most basic non-relativistic equations that offer basic calculations of the forces and fields are...
  40. Sibilo

    I Does the Skin Effect cause charge to accumulate on the surface of a conductor?

    good morning gentlemen, I would like to ask you a fairly simple question but which I am unable to resolve. Then considering the "skin effect", which involves an increase in resistance to the passage of current with consequent generation of eddy currents, this leads to an accumulation of charges...
  41. K

    Is grounding necessary when running off of batteries?

    Hi all, playing with fancy e textiles and I wish to run a current through it. I don’t want to use mains, or d cell batteries. Can you point me in the right direction what components I could use and also how to get away with any grounding as it’s just a small area to put a current through...
  42. student_man

    Engineering Current change after inserting thin conductive foil into resistor

    I tried splitting it up into 4 individual resistors, adding them up (each side serially and then both sides with each other as parallel) and then using V=IR but it ended up being the same current as the original. (The answer should end up being (9/8)* the original current)
  43. H

    Ohm's Law confusion -- How to handle an incandescent bulb?

    I know that Ohm's Law gives me the answer of 0.25 A but what I don't understand is how is it ok to use Ohm's Law when I know that the lamp doesn't obey the law? I know that as the current is increased through the lamp, the resistance increases due to temperature rise which, I am told, makes it...
  44. Hak

    Coaxial semi-infinite solenoid and superconducting disc

    I have no idea how to deal with the problem. Do you have any hints, please?
  45. PhysicsTest

    Are the Battery Capacity Calculations for Electric Vehicles Correct?

    Battery Capacity = Current * Time Power = 400 * 750 = 300000 Watts V*I = 300000 I = 300000/300 = 1000 Amps Battery Capacity = 1000 * 1 = 1000AH. Are the calculations correct? Why the battery capacity is defined in Amps?
  46. D

    AC generator, current and ground

    Hi, Let's say we have a basic AC generator, where a single wire is rotated within two magnets: Due to the electromotive force, a voltage is generated so that Va - Vb = 120V. Let's now ground Vb side directly to earth, while leaving Va still open: We can say that Vb = Vc = 0V and Va...
  47. P

    Electrical Help with detecting current/voltage with a coil and a spinning magnet

    Playing around with electricity and magnetism. Well, trying to anyways. Wound some wire up and down the length of a 4" screw several times. Thought when I spun the magnet close to the coil I would get a detectable amount of current on my voltmeter. Anyone know why I'm not reading anything? I...
  48. casparov

    Calculate the Magnetic Vector Potential of a circular loop carrying a current

    Can someone explain what exactly happens at (4) ? I do not clearly follow, except that there is some cosine law going on? I also do not really understand why at (3), r' doesnt have a z hat component, but I can live with that.
  49. A

    Bidirectional current switching with single type transistor

    So here is my dilemma. I have a test setup with multiple coils all lined up in parallel in such a way that one end of each coil is connected together while the other is connected to a switch (mosfet) the switches then connect each coil to ground but that ground can become + based on which coil...
  50. gurbir_s

    I Angular momentum associated with a current carrying circular wire

    How should I calculate the angular momentum carried by a current carrying circular wire? Is it correct to consider the angular momentum of the electrons moving with drift velocity? Like ##L = n m_e v_{drift} r## where ##r## is radius of the loop, and ##n## is total number of electrons moving in...
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