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. S

    Beam current of positrons and electrons

    a) My idea is: 1. Find the energy created by annihilation process, which is ##E=2mc^2## where m is the mass of electron 2. Find the wavelength of photon by using formula E = hf 3. Find the speed of positron by using the formula of de broglie wavelength 4. Find the p.d by using conservation of...
  2. anubhavsingh

    Reverse saturation current and leakage current in a BJT

    I have been studying Studying Donald Neamen's Electronic Circuits 4th edition and Sedra Smith's Microelectronics 7th edition for quite some time now. I have been self studying. After searching extensively on Internet as well as trying to understand from the books, I have not been able to...
  3. L

    Earth grounded, where does the current flow?

    My questione are these: -If i have a voltare source (like a battery) that supplies a 5V voltage difference between its terminals, and there is a parth from positive to a resistor and then to ground, with negative terminal not connected: the current flow to the ground?( I believe because there is...
  4. Q

    I What is the current status of Many Worlds?

    Despite its lackluster reception at its conception by Hugh Everett and subsequent advocacy by Bryce S. DeWitt the concept of "just take the theory seriously" and intriguing science-fiction concept of parallel worlds eventually gave it a major resurgence, much thanks to David Deutsch's pioneering...
  5. A

    I Induction heating vs Current heaing

    I've been thinking and can't come up with a satisfying answer. Would there be a difference in the amount of heat generated in a given time in a metal rod if it was heated by a) induction b) current passing through the same length of rod Given that the current is the same amperage and...
  6. D

    Engineering Alternating current circuit with transformer

    Hi, I don't understand how to solve the problem below for (a). First I transform the cirucuit to direct current problem using jw method. Now i see that U=-I2Z. Z=R2+Zc3=R2+1/jwC3=4,5+1/[j(1000)(10^-3*0,25)]. Then I use impedance transformation to get rid of the transformator(using Z0), but then...
  7. R

    B According to current physics, is vacuum still something or nothing?

    Before that, Lawrence Kraus stated "Empty space is a boiling, bubbling brew of virtual particles that pop in and out of existence in a time scale so short that you can't even measure them" . After reading https://www.physicsforums.com/insights/physics-virtual-particles/ especially this statement...
  8. MRB29

    Programs Grad prospects of a current International Senior in HS

    Hello everyone, [I underline portions of the text that are most essential to my enquiry ( 2 questions at the bottom). I immensely appreciate the generous act of reading everything otherwise.] Background Info: North African, female-identifying, 16, below average ECs, no awards, no notable...
  9. N

    Calculate the individual voltage, current and power in series and para

    To determine the voltage I did voltage/number of globes: 24/16 = 1.5V per globe - Not sure if this is correct or not To determine current, I figured out using resistance formulas that the resistance for each set of 8 globes is 15 ohms R = V/I 24/3.2 = 7.5 ohms total resistance 7.5-1 = 2 * 15-1...
  10. A

    Klystron beam current, drive frequency, LHC CW example

    First of all I want to ask , do the LHC power klystrons work always in CW or are their frequency shifted to correct for timing of the bunches in the LHC tubes in case something isn't aligned or doesn't that ever happen? Also how do they drive the klystrons at LHC or other CW operation from an...
  11. jjson775

    Induced current in a wire loop embedded in a changing B-field

  12. F

    Can current gene editing technologies reverse age related mutations?

    How can current gene editing technologies like Prime Editing can be used to reverse all age related mutations that negatively affect some type of cell like neurons?. According to this article (you need to click on the "toggle reader view" button in firefox in order to read it without registering...
  13. Anmoldeep

    I Work Done in Changing Shape of Current Carrying Loop

    How would you go about calculating the work done in morphing a square current-carrying loop into a circular current-carrying loop, without change in length while maintaining the same angular orientation with an external magnetic field. My book suggests defining P(potential energy) = M.B (dot...
  14. T

    I How a Battery creates a Potential difference in an electrical current

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  15. E

    Relationship between magnitude of current and magnetic field

  16. S

    Current and resistance in the power loss of a transformer

    a) Output voltage = 2 x 6 = 12 V Current in R = 12 V / 13.5 kΩ = 8.9 x 10-4 A That is the correct answer based on the solution but I don't understand why when calculating the current in R, the resistance of secondary coil is not considered. I thought it should be like this: Current in R = 12...
  17. P

    I Energetic argument for the tension in a current loop

    The energy stored in a current loop equals ##\frac{LI^2}{2}##. From a dimensional argument, it follows that the inductance grows with the size of the loop. This would mean that, if we assume the current stays constant, enlarging the loop would require external positive work, so, the force...
  18. baby_1

    Violate current conservation in Perfect Magnetic Conductor (PMC)

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  19. V

    Current due to magnetic monopole passing through a wire loop

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  20. S

    Shielding Dirty Electricity Ground Current

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  21. LCSphysicist

    The current state of physics and comparing it with the past

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  22. P

    Magnetic field - General current in a cube

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  23. E

    A.C. generator -> why does the current reverse?

    why does the current reverse when the coil is at this position in A.C generator ?
  24. I

    Current in RLC Series Circuit: Need Help

    So am trying to find the current in the RLC series circuit ,but i think i have done something wrong ,if anyone could tell me where i went wrong ,it would be great ,thank you Resistor-100ohms Capacitor-0.01uF Inductor-25mH Voltage Source-50v a.c 1kHz
  25. I

    Calculating Current in a Series RC Circuit

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  26. F

    I Why is initial current zero in an RL circuit with an emf?

    Why is initial current zero in an RL ciruit with an emf, but it is not in a charging RC circuit?
  27. F

    Magnetic field generated by a current in a wire - special relativity

    First I wrote in ##S'##, by using Gauss theorem $$ \int_{\Sigma} \underline E' \cdot \hat n d\Sigma = \frac Q {\varepsilon_0} \rightarrow E'(r)2\pi rH=\frac{\lambda'H}{\varepsilon_0} $$ $$ \underline E'(\underline r)=\frac{\lambda'}{2\pi\varepsilon_0r}\hat r $$ Its components are...
  28. cheniour oussama

    Simulate Leakage Current - Reverse Bias Diode

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  29. LCSphysicist

    Noether Current: Understanding 2.10 & 2.11

    I just don't understand what happened after (2.11). That' is, the second term is zero, so we have $$\alpha \Delta L = \alpha \partial_{\mu} ( \frac{\partial L}{\partial (\partial_{\mu}\phi)} \Delta \phi )$$ So, second (2.10), isn't ##\Delta L = \alpha \partial_{\mu} J^{\mu}(x)##? So shouldn't...
  30. cemtu

    What makes up a "current" in solid state physics?

    If there is some incoming light that has hit electrons of a N-type doped silicon and broke loose these electrons from their covalent bounds and excited them to the conduction band and also excited the electrons in the donor energy level to the conduction band as well, here we know that, the...
  31. B

    Torque Production in Eddy Current Motors

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  32. Wrichik Basu

    Gain limiter circuit in LTspice - current flowing in wrong direction

    This is one more thread in my quest to learn simulations in LTspice. I am trying to simulate the gain limiter network shown in this video. A snapshot of the video is available for quick reference: My schematic in LTspice is shown below: For the simulation, I am using DC sweep on voltage...
  33. R

    Is Current in Superconductors Truly Infinite?

    Hello! Recently, I became interested in superconductors. And I talked to professor in my uni. Here's my question, since superconductors have zero resistance by definition, so, in stable condition (after passing transient phase) the current should be infinite. Which implies that according to...
  34. Osnel Jr

    Transistor theory question involving the base current

    Help
  35. D

    Problems about magnetic field, electromotive force, induced current

    Hi, I was practicing some problems on the magnetic field and the electromotive force, when I got stuck on these two exercises. Could you help me figure out how to proceed? In the first problem, I tried to find the magnetic field flux by multiplying the induced current for ∆t and R. Should I now...
  36. A

    I How do Cooper pairs carry a current with zero net-momentum?

    One of the first starting points of introducing BCS theory in a superconductor is applying a theorem stating that the ground-state of a quantum system has an expectation value for its momentum of zero. You then use this to say that an electron must pair with another electron of equal and...
  37. K

    Relationship between closing a switch and the total battery current

  38. Lucas123

    Engineering Solve Motor Coil Current at Startup & Full Speed

    The question I'm in doubt about is The motor coil has a resistance of 10 Ω and is powered by a voltage of 120 V. When the motor is operating at rated speed, its emf is 70 V. Thus, it is questioned: a) What is the coil current when the motor is started? b) What is the coil current at rated...
  39. P

    Current generated by plasma of uneven density in a Magnetic Field

    I am only asking about part (b)(i) and (b)(ii). Below is the explanation for (b)(i). What is going on in the above? I understand up till the 3rd line, about the left/right hand circular motion. What is the "upward motion" the solution mentioned? Is it suggesting that ions are moving...
  40. P

    EM fields and Current between 2 charged cylinders

    The task is to find the magnetic field between the 2 long cylinders, which extend to infinity. Integration is involved to find the total current passing through the Amperian Loop shown below. What I do not understand is why only sides 1 and 3 contribute to that B ds part of Ampere's Law. Isn't...
  41. L

    Help calculating the current from the density and a rotating frame

    hi need help in physics HW: given current density [J][/→]=[J][/0][x][/Λ] and rotating frame with given surface vector: $$ A^→ = A_0(cos(wt)x^Λ + sin(wt)y^Λ$$ in need to calculate I(t) i tried I = ∫J*dA but i don't know i to technically do the math please help me
  42. H

    Exploring Current, Voltage & Z When Frequency Increases

    https://www.physicsforums.com/attachments/6-png.282284/?hash=0362cb24c9a8ed9b3ee9efab56a28e3d If the increasing frequency leads the current amplitude to increases, then Z decreases because V = I*Z and V remains unchanged...
  43. H

    The Direction and magnitude of current in the inductor

    I understand that the current is going rightward because of the negative sign in the equation above, but why is the current increasing not decreasing? The current doesn't stay constant because it changes with the time based upon the equation above again.
  44. H

    The net current through a circle of radius R, in the xy plane and centered at the origin is given by?

    Here's what I did: ∮ B * dl ＝μ0 ＊ I ∮ AR * 2π*R ＝μ0 ＊ I ∮ 2π*AR^2 / μ0 = I ∮ 2π*AR^3 / 3μ0 = I Where did I do wrong?
  45. Tim86

    DC current through a resistor circuit

    Summary:: Current through a certain resistor in a mixed dc circuit. Hi, Sorry if this is the wrong forum. I'm trying to work out the current through R1.The answer I need is 2 Amp, which I have confirmed with a simulation software. I have calculated the source current as 8A, the current past...
  46. I

    Find the time required for the current to grow to 2.5A....

    what is the equation on finding the ''The time required for the current to grow to ...Amps'' i was asked to find The time required for the current to grow to 2.5Amps ,and i found out that its some where around 174.38ms, using Ltspice, but i want to find it out by calculating it out.
  47. S

    If an electron is repelled by another electron how do we get current?

    As we know that An electric current is a flow of electric charge in a circuit and In electric circuits the charge carriers are often electrons moving through a wire. Now, since we know that Like charges repel each other then how do the electrons flow through a wire since they are like charges...
  48. S

    Convection current in electricity

    So, I randomly came upon this in a textbook that I was skimming and I think I have a very very surface ideea of what it's about but I want to read and know more in order to understand the fenomenon in much more detail. Any help in any form would be much appreciated! P.S.: This is my first post...
  49. I

    DC versus AC current in a coil

    Hello, am kind of new to all the physics stuff , and kind a terrible at maths but am trying my best to be good at it one day .So i was told to answer this question When a direct current of 2A is passed through a coil, the potential difference across the coil is 20V. When an alternating current...
  50. I

    Phase shift between voltage and current

    Hello ,so am trying to find a phase shift between voltage and current ,I've done what do i do after that ?and is this right ? Q A 100Ω load is connected to a power supply of 100V at 50Hz. At time, = 0, the instantaneous value for voltage across the load was zero and the current through the load...
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