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.

View More On Wikipedia.org
Recent contents Top users
  1. 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.
  2. 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 ?
  3. 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...
  4. 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...
  5. 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...
  6. 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?
  7. 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...
  8. 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...
  9. 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...
  10. 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...
  11. 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...
  12. 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...
  13. 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...
  14. 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...
  15. 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...
  16. 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...
  17. 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...
  18. 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...
  19. HAgdn

    Behavior of Current in an AC mains wire

    No attempted solutions.
  20. 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...
  21. 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##...
  22. 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!
  23. 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?
  24. 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...
  25. B

    Working out the current flow in a wire

    Hi there! I have recently been given this question by my teacher as shown below I'm struggling to see the set up arrangement for this circuit This is what I have drawn so far How would I fit in the third wire here and ensure I have closed loop circuit so that current can begin to flow...
  26. R

    Can cell electrodes in series share the same current collector?

    Sorry if the answer is obvious, but I was wondering if positive and negative electrodes (cells in series) can share the same current collector as depicted below? I want to create a 12V battery with cells inline in series without creating cells with individual current collectors. Note that the...
  27. W

    I Why induction requires a magnetic material to produce a current

    I can create a fairly strong magnetic field by leading current through a copper coil. However, I cannot then with that magnetic field create a current (not a useful one at least) in an object made out of copper. I understand that this is because copper lacks of magnetic properties. For instance...
  28. Saptarshi Sarkar

    Intuitive way to understand ideal current and voltage amplifiers

    I was reading about ideal current and voltage amplifiers and the book says that an ideal current amplifier should have 0 input impedance and infinite output impedance while an ideal voltage amplifier should have an infinite input impedance and 0 output impedance. I am not quite sure I...
  29. P

    Ampere's Law Problem: B-Field from a Current Distribution

    This is the problem, first time i am attempting the Ampere's law problem From the above question this is my attempt, the picture is ∫B.ds = μ*Ienc; ----> Ampere law , where Ienc is the current enclosed in the amperian loop. I assume the circle as the amperian loop, is it correct? Can i...
  30. VictorMedvil

    A Superconductivity: Current and Magnetic Field Limitations

    Why when a certain current limit is breached is superconductivity destroyed in a material, what atomically causes this effect when J > Jc? Secondary question what causes H0's value to be higher or lower atomically and chemically for a given material?
  31. B

    Working out the current and voltage in a circuit

    Here are a few problems I have been trying which are shown below Here is what I have done The correct answers for these Q's are: I'm not sure what I have done wrong for Q4, I assumed that all 12 cells were connected in series thus each individual emf sums up to 24V Similarly the...
  32. SchroedingersLion

    Batteries: Is the current a diffusion current?

    Greetings, I realized that I don't understand a fundamental fact of common Li-ion batteries. During the charging process, electrons are forcefully extracted from the cathode and pushed into the anode. Charge balance then yields a flow of positive Li ions from the cathode to the anode (through...
  33. Andrea Vironda

    Why in an RL circuit does the voltage anticipate the current?

    In my idea the tension change after connecting the circuit to a battery is immediate, while the current takes some time before moving. That should be sufficient to prove my question but, so why in a RC circuit the opposite happens?
  34. paulmdrdo

    Finding the output impedance of Current Controlled Current Source

    Summary:: I was trying to derive the equation for the output impedance of the ICIS circuit. Here's what I've tried so far. What I have derived does not agree with the one provided in my book. Since it is a current source the negative feedback must increase the output impedance. The one I...
  35. Alefan_

    Average current around a magnetic loop that changes its shape

    To find out what the induced loop current was i used the formula: V=R×I To find out what the value of V was i used the formula that links electromotive force (fem) to angular speed: Fem=ω×B×A The only thing that's missing is the loops area but considering that it's a semicircle and that the...
  36. J

    Engineering DC bias current and small-signal resistance

    We are given that ##i_D = 8\cdot 10^{-12} (e^{v_D/20m} - 1)## Hence ##i_D' = e^{50 v_D}/2500000000## and ##i_D'' = e^{50 v_D}/50000000## Then I have that ##\delta i_D \approx\frac{ e^{50 v_D}}{2500000000} \cdot \delta v_D = \delta v_D / 5## Cancelling ##\delta v_D## from boh sides and solving...
  37. J

    Engineering A circuit with non-linear devices

    I honestly don't know how to quite even begin this problem. Looking at Fig 3-2, the slopes of the graphs are 1/R, and hence where the slopes are 0, we have infinite resistance, in which case current wouldn't flow through that resistor and hence simplify the circuit. So I was trying to find...
  38. J

    Engineering Finding voltages in a linear circuit

    From the circuit I have: ##-v_b + v_a + V = 0## ##v_b - V = v_a## ##i_1 = (v_b - V)/R_1## ##I + i_2 = i_1## ##(v_b - V)/R_1 = I + v_b/R_2## From this last equation I get ##v_b = 10.8## and hence ##v_a = 5.8##. However, apparently that is wrong. (And hence my answers to #2 were all wrong as...
  39. Decimal

    Magnetic vector potential of a moving current sheet

    Hello, I start by applying the integral for the vector potential ##\vec{A}## using cylindrical coordinates. I define ##r## as the distance to the ##z##-axis. This gives me the following integral,$$\vec{A} = \frac{\mu_0}{4\pi} \sigma_0 v 2 \pi \hat{x} \int_0^{\sqrt{(ct)^2-z^2}}...
  40. J

    Finding the missing current and voltage in a circuit with superposition

    I don't get this. Since we have analyzed the circuit separately for each source, adding them should give me the final values of I1, V2, I2, V1 etc. However, that's not quite true—from cases 1 and 2, I should have I1 = 4 + 5 = 9 mA, but it's 8mA. Hence, I thought that the black box consumes 1mA...
  41. J

    Thevenin isolates nonlinear element

    I have no problem getting the ##R_{TH}## since from the special element's POV, the resistors are in parallel, and that's the answer. However, I don't really understand how to get ##V_{TH}##. Ignoring the special element, it seems that I have the resistors in series this time. But I'm not too...
  42. J

    A Circuit with Nonlinear Element—finding element's current & voltage

    I don't really understand or see the correct way to approach this. Letting the current in question be ##i_x## (as shown in Fig. 1), and the unknown (changing) resistance be $R_x$, I can write: ##-V_s + R_s i_s + i_x R_x = 0##, and ##R_p i_p = i_x R_x##. Hence we can also write ##-V_s + R_s i_s...
  43. J

    Conventional current, magnetic fields and magnetic poles of different diagrams

    I need to do question 1. I understand the right hand rules but am lost on what to do here.
  44. J

    Circuit Analysis of a diagram with series and parallel circuits

    I found the Req which is 13.6 and also found the It which is 0.74. I'm having trouble finding the separate current and potential difference numbers.
  45. Y

    Find the RMS current drawn from the 240 Vrms supply

    My first idea was to find the total impedance of the circuit, but I think viewing the two parallel resistors as one resistor of 0.5 Ohm isn't the correct way? I don't know how to simply this series / parallel circuit further to find Z total. Then I tried to use Kirchhoff's law to the loop on...
  46. A

    Induced/eddy current cancelation in a loop

    Hi, I have a theoretical problem, I am wondering would it be possible to cancel the otherwise induced currents within a planar sheet/foil conductor. you can see in the image I have a flattened conducting sheet which in the middle is split up in individual smaller conductors (for the sake of...
  47. F

    Power, current, voltage transfer principles

    Hello, I have been reading about impedance matching as being the main requirement to ensure maximum "power" transfer from one part of a circuit to another: the two electric systems ##A## and ##B## need to have complex conjugate impedance so only 50% of the energy is reflected back at their...
  48. johnboyman

    Trying to calculate the peak current of a Capacitor bank

    Hello I am building a Tesla Coil. I built it well I attached an image of the circuit I used. I bought a 15,000 volt transformer rated at 30 ma. I think it is too small for my tesla coil because it keeps blowing a fuses and a red light turns on. Here are the specs. -Inductance (L): 17 uH...
  49. J

    A Current spreading decreases resistance?

    I have a Question to the Independence of the probe distance for a four-probe-measurement technique. In a paper the author is argument that the resistance of a 2D shape is NOT dependent of the distance between the probe which measure the voltage drop, cause he says that the current spreading...
  50. C

    Does Polarity and Current Direction Affect Energy Flow in AC Circuits?

    I assume that because there is a resistance, the polarity of the voltage must be the same as the charge flow, and thus the current, in order for energy to flow in the same direction. For instance, could I use the example of a light bulb (the resistor) plugged into AC lines; we know that if the...
Back
Top