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. DaveC426913

    What could be causing electric current on my laptop case?

    I thought there was a tiny metal burr on the corner of the lappie, and I kept scraping my forearm across it. Then I thought I had a tiny metal shaving in my skin that I kept brushing on the corner as I typed. Turns out, that little pinprick I'm feeling is electric current. I can only feel it on...
  2. G

    Confusion on the magnitude of magnetic fields

    Here, the correct options are A,D. Solution: I got A as answer as ∫ B.dl=µI. But, the answer to the question says that it is a solenoid and therefore Bx=0 for point P. Here I'm a bit confused. I know this system resembles a solenoid in some ways, then By must have some finite value, but...
  3. C

    Circuits and the percent change of current when the switch is closed

    For an ideal battery (r = 0 Ω), closing the switch in (Figure 1)does not affect the brightness of bulb A. In practice, bulb A dims just a little when the switch closes. To see why, assume that the 1.50 V battery has an internal resistance r = 0.30 Ω and that the resistance of a glowing bulb is R...
  4. C

    Percent Change Of current when the switch is closed

    (.174A-.181A)/.181A=-3.86% but it says it wrong, and I did (.181A-.174A)/.174A =4.02% but this was wrong too. I've tried 3.87%,3.86%,-3.87%,-3.67%,4.02%, and -4.02% but all were wrong. I'm really not sure what to do here.
  5. F

    Current is not continuous in RC circuits?

    Now that currents don't flow past the interior of capacitors at any time (charging/discharging etc), currents should be functions of a spatial coordinate, i(x), in that i(x) is non zero in wires and 0 in capacitors. But in circuits usually currents are assumed constant in the same branch. What...
  6. K

    E&M: Field of a Wire with non-uniform current

    Summary:: Not sure if my solution to a magnetostatics problem is correct [Mentor Note -- thread moved from the technical forums, so no Homework Template is shown] I was trying to solve problem 2 from...
  7. H

    Electric dipole moment vs electric current dipole moment

    I have to estimate the electric dipole moment of an NV center in units of Am. I know that for a regular electric dipole moment it can be estimated using p=ed. With e=1.6*10^-19 and d=0.1 nm (interatomic distance), this however is in units Cm. I don't know how to go to Am
  8. mcastillo356

    Why does current need to vary in an inductor?

    In a power transformer, the variation of the current in one circuit induces a current in the other. This cause-effect relationship is two ways. If circuit A affects circuit B, then B circuit will affect A circuit; this is the cause of the concept of mutual inductance. However, it's not necessary...
  9. F

    Electric current is not a vector while electric current density is a vector

    Why is electric current not a vector while electric current density is a vector? What's the intrinsic difference between the two through that surface integral?
  10. F

    A Relation between Dirac's equation density matrix and current with spin

    After computind dirac 1D equation time dependant for a free particle particle I get 2 matrixs. From both,them I extract: 1) the probablity matrix P =ps1 * ps1 + psi2 *psi2 2) the current matrix J = np.conj(psi1)*psi2+np.conj(psi2)*psi1 I think that current is related to electricity, and...
  11. B

    Engineering RLC Series Network: Impedance, Current, Power Factor, Phasor Diagram

    Hello. I have completed the following question. My answer: i) Circuit Impedance Reactance = XL = 2 x pi x F x L = 2 x pi x 50 x 0.15 = 47.12 Ohms Reactance of Capacitor = XC = 1/2 x pi x F x C...
  12. Wrichik Basu

    What is the meaning of "Long time maximum output current ≥ 1.5 A"?

    I am looking at the module HLK-5M05, which is a ##5\ V, \ 5\ W## AC-DC power supply module. The advantage of this module is that, it does the stepping down and rectification within itself, and is a switching source, so fluctuations in the voltage grid won't affect the output (at least that's...
  13. mcastillo356

    Electromotive force when current is alternating

    Hello, let's imagine a generator as shown in image. I just don't understand alternative current. -\epsilon shouldn't be always positive? Otherwise, how can it provide anything? Thanks
  14. S

    Current Induced in one circuit by another circuit

  15. f95toli

    Pass current to "burn" stray vias?

    A while back I designed a fairly expensive 3-layer PCB (gold plated RF laminate, not cheap). Unfortunately, we have now discovered that I've accidentally put a stiching via, i.e. a vias for connecting top and internal ground planes in the centre of an important RF line which is now permanently...
  16. G

    How to get the magnetic moment for this loop?

    About this figure, the current in the opposite wires are parallel (and not anti-parallel). So, for instance for the first option the torque is zero; but I wanted to know what is the magnetic moment of this loop. Since I rely only on formula I've have no idea how to compute for this one.
  17. zoyash

    Electric Current and Resistance

    I have attached my solution to this problem but I think I got the wrong answer.
  18. T

    I Probability current density of a stationary state

    I have written a finite difference program to solve 1D time-independent Schrodinger equation. It seems to work correctly for harmonic oscillator, particle in a box, etc. But I can't figure out how to calculate the probability current density. It should be constant, but what is it? The program...
  19. Leo Liu

    Torque on a circular current loop

    Can anyone please tell me why the torque on a circular current loop can be calculated by the equation below? In other words, what is the intuition for the formula? Thank you. (I modified my question to a particular case) $$ \vec{\tau} = I \vec{A} \times \vec{B} $$
  20. Elder1994

    Magnetic field due to the current flowing in a bent wire

    Hello, in this problem I'm supposed to calculate de magnetic field due to a bent wire at any point of the x-axis after the bending of the wires. It is obvious that the part of the wire that is parallel to the x-axis makes no contribution to the field so we can focus on the other part of the...
  21. M

    Two batteries and two resistors circuit - wrong possible answers ?

    It's ABCD question with answers attached. Problem is that, I don't think that neither of those are correct. From KVL the equation seems to be i = (E2-E1)/(2r1+2r2 + R). I've attached images of the circuit, answers, and my solution. Can someone please point me if I am wrong, and if yes, where's...
  22. B

    Why does a thyristor keep conducting after removing the gate current?

    i have seen several videos of thyristors but they never really explain the fundamentals they just say that cause there is a current flowing in there it keeps being on but why does a transistor then turn off when you remove gate voltage
  23. xWaldorf

    How does a current "know" where to go

    Let's say we have a circuit, and in that circuit there's a resistor, and there's a wire that goes around it so that the current can flow freely without getting to the resistor. my question is this: how does the current "knows" to flow towards the around the resistor? how does it know not to get...
  24. G

    A confusing question on capacitors and voltages across them

    In my opinion, the voltage across the C1 should be 9V as the potential on the side of the positive plate of the capacitor should be (15-6)V and on the other be 0V. Similarly the potential across C2 should be (7-0)V. Here I'm basically assuming that the voltage at the negative terminals of the...
  25. L

    Energy, current and electrical potential of a particle accelerator 🎆

    Hello, I have answered the question below but would like some advice on whether I can improve my answer or if anyone is able to check whether I have made any mistakes ? i. 1 V = 1eV in a 1:1 relationship, therefore; 6.5 TeV = 6.5 TV = 6.5 *10^12V ii. E=W W=V * Q Q=number of particles * charge...
  26. nineteen

    What is the standard definition for what an "electric source" is?

    The syllabus states : "Explain that the potential difference which is needed to apply across any electric circuit to flow current is supplied by an electric source". To explain this and make notes, I want to first understand what an electric source particularly is. And how all those electric...
  27. Physics lover

    Eddy current Losses due to different materials

    I know only about Laminated,Iron and wooden coil.I don't know what is Air cored coil. So according to me,it should be Wooden cored coil because less current will flow through wooden cored coil.Ans it will be maximum in Iron cored coil. Please tell,am I correct or not?I don't know the answer.
  28. A

    Compass , current carrying coil

    a. No, because only permanent magnets are suitable to be used as a compass. b. Yes, but only if the coil doesn't have an iron core. c. Yes, but only if the coil can turn easily. I choose (c) , Is that correct ?
  29. JD_PM

    Get the current and the EQs of Motion of the Dirac-Lagrangian density

    a) Here I used the definition of current (reference: Tong notes, page 14) $$j^{\mu}_{\nu} = \frac{\partial \mathcal{L}}{\partial (\partial_{\mu} \phi_a )} X_a (\phi) - F^{\mu} (\phi), \ \ \ \ \ \ \ \ \delta \mathcal{L} = \partial_{\mu} F^{\mu}; \ X_a (\phi) = \delta \phi_a$$ In our problem we...
  30. T

    Why do you need a line 2 on an Alternating Current circuit?

    Preface to thread: The power source in both diagram 1 and diagram 2 is a wall outlet with alternating current power, not a battery. The load in both diagram 1 and diagram 2 is a light bulb, even though I forgot to label the load in diagram 2...
  31. Yani Botsanovski

    Eddy current calculation question

    Hello there! I have seen some great eddy current brakes and wanted to learn more about it. The problem in the internet I can not the specific case I have in mind. I searched the internet and found a great deal of material about magnetic forces. I cannot, however, find the specific case I'm...
  32. J

    In an LC circuit the current does no drop to 0

    in an LC circuit the current does no drop to 0 but varies sinusoidally. The capacitor is recharged with a different polarization. Why is this so?
  33. Noki Lee

    I Valley degeneracy in tunneling current

    I'm trying to understand the valley degeneracy to calculate the tunneling current. Here is the equation of tunneling current.$$I_T=q\frac {g_sg_v} {L} \sum_{k} v_g(k)(f_v-f_c)T$$ ##g_v## is valley degeneracy. I thought it comes from the symmetry of structures, depending on a certain point in...
  34. C

    Potential vector (A) of a disk with a surface current

    Hi, I've been stuck for a long time with this exercise. I am not able to calculate the potential vector, since I do not know very well how to pose the itegral, or how to decompose the disk to facilitate the resolution of the problem. I know that because the potential vector must be parallel to...
  35. Adesh

    Why does the current have no ##\phi## component in a toroidal coil?

    These are images from the book Introduction to Electrodynamics by David J. Griffiths . . . My problem is that I'm unable to understand how the current has zero ##\phi## component (I have underlined it in the first image)? I do understand cylindrical coordinates, I know...
  36. L

    Medical What makes the current coronavirus different from the others?

    An interview on NPR with virologists discussed the reasons that this current viral pandemic is different than others in the past. Key differences were: - Ability to make new viruses - apparently 1000 times more prolific than flu. - Unlike flu viruses, it does not appear to mutate because it...
  37. F

    Induced EMF and current for a bar sliding on a circular rail

    On the left: my copy of the illustration in the problem. On the right: top view, with the angle. The problem gives the magnitude of the magnetic field, the radius of the rail, the resistance of the resistor, the initial rotational frequency of the bar. I am able to obtain the given solutions...
  38. K

    Calculate the current in all parts of this electric circuit

    In the circuit below, the output is 23 W across the resistor with the resistance 6 Ohm. Calculate the amount of current in all parts of the circuit as well as the polarity and EMF ε of the unknown battery. Circuit: My attempt: I get 6 unknowns with 5 equations. I don't know how to find the...
  39. F

    Arbitrariness of the surface involved in the displacement current

    I was thinking of a standard, high school level discussion of the displacement current. The need for introducing this quantity is demonstrated by considering a circuit with a charging capacitor, and (for the sake of simplicity) a circular loop whose axis is along the (straight) wire carrying the...
  40. HAgdn

    Total Current running through a wire due to the drawn currents

    I made this scenario where I am looking for the total current running through a wire (I_0). I am also trying to model the current running through the wire (I_0) considering the harmonics contributed by the four loads. But since Fourier stated that a complex waveform is the discrete sum of some...
  41. K

    Voltage measurement on a Current Transformer (CT)

    I don’t know the ratio of the CT. I’m just looking for an explanation on this. I thought in order to measure output voltage you need to pass the current through a resistor and read the voltage drop. A co worker put 400a through the CT and measured 130v. Something just seems off to me. Can you...
  42. HAgdn

    [Equation Validity] - Current Characterization (AC) in Sockets

    I = A_0 * sin(n_0wt + p) + A_1 * sin(n_1wt + p) + ... +A_n * sin(n_nwt + p) Looking at the equation, it only contains sinusoidal waves. Further, there is the possibility of waves having the same shift or no shift at all and even, having the same frequency. Is it really valid or correct to use...
  43. Boltzman Oscillation

    Must a load consume the entire available current or only what it needs

    So if I have a source of 5V and 20 amp then the maximum power I can get from the source will be: $$ P_{max} = 5*20 = 100W$$ but my load can only take in 5 watts, it will blow up. But, does this have to happen or does my load only take what current it needs? My guess is that the load takes in...
  44. K

    Vacuum interrupter contacts and displacement current

    I’m self taught so I have a lot of holes in my understanding. I also have little to no mathematical understanding. Even though ironically, I tend to prefer to picture electricity as numbers rather than “water” in a pipe, etc. I’ve been studying displacement current recently and have a question...
  45. HAgdn

    Behavior of Current in an AC mains wire

    No attempted solutions.
  46. Z

    Aerodynamics - why wings create lift - current vs historical discussions

    My son and i were discussing aerodynamics and he brought up a paper from https://phys.org/news/2012-01-wings.html It seems that the latest discussions seem to completely discount the differential velocity of air flow as a cause of differential pressure, but point to a differential pressure...
  47. E

    Why do we even need the term 'conventional current'?

    If we take electric current to be the rate of flow of (signed) charge past a certain point in a given reference direction, this unambiguously tells us all the information that we need to know. If we label a current arrow with ##-6A##, then in ##1## second we either think of a charge of ##-6C##...
  48. B

    Calculating the current through this load resistor

    Hi everyone I have drawn what I think what the setup should look like, and worked out the equivalent resistance of the parallel connected resistors Not so sure where to go next with this problem? Any help would be greatly appreciated!
  49. D

    I Is the four current in Relativity an invariant quantity?

    Is the four current in relativity an invariant quantity? I know the divergence is zero for the four gradient, i.e. the continuity equation. But is the four current a vector in the sense that it has invariant properties?
  50. M

    Inducing electric current in a wire (a comparison)

    Consider the following experiment: from a lacquered copper wire we cut off twenty to thirty pieces of about 10 cm. From them we form a bundle of parallel wires and connect the two ends with one more wire each. The other ends of these two wires are connected to a sensitive analog ammeter. We hold...
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