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. Asmaa Mohammad

    The phase difference between current and voltage.

    Homework Statement An inductor (Xl = 40.2 ohm) is connected in series with a resistance (30 ohm) and and an AC source ( 10V , 80Hz) and the current flows in this circuit is 0.2 amp. How could you reduce the phase difference between current and voltage to zero without changing the value of...
  2. D

    Engineering Laplace tranforms, transient current series CR circuit

    Homework Statement A step voltage of 120v is applied to a series CR circuit. R = 20KΩ, C = 4µF 1. Deduce, using Kirchoff's voltage law and Laplace Transforms, an expression for the transient circuit current. 2. Using the equation obtained in 1. deduce the equations for the transient voltages...
  3. M

    Sizing a Solar Array To Boil Water

    Hello, I am having a hard time deciding the size of a solar array to boil water for a school project. Before putting any thought into the subject I simply thought that I would just take the wattage of the panels and add them up since they are added in both series or parallel and then select an...
  4. T

    Increasing voltage regulator current

    I'm looking to draw about 6A. I have an LM338 regulator that can supply up to 5A. Searching the internet I came across this schematic, So basically when the 1R resistor drops 0.6V then the transistor conducts the remainder of the current. I calculated my own values for those two resistors. Was...
  5. Buggsy GC

    How will the voltage, current and resistance be distributed

    I have a lab to work through tomorrow morning and i need to be able to explain how the voltage, current and resistance in the compound circuit diagram below is distributed, and write an equation which can be used to measure the total resistance of the circuit. I know that when you normally try...
  6. E

    LiPo battery peak current burst C rating

    Hi, as I know the burst C rating usually refers to the max current allowed for 10 seconds. if I need higher current for 1 second, I can do it? The heat is the problem here?
  7. nothing909

    Types of eddy current couplings

    Homework Statement I have a really simple question, state two types of eddy current couplings and state a flexible coupling, but I've been googling it for the last half an hour and can't find an answer. The Attempt at a Solution Can anyone tell me two types of eddy current couplings? I know...
  8. Kelsi_Jade

    After 14ms the current drops -- Find the capacitance at C

    Homework Statement Here is what I have so far. Am I going the right direction? If so, how do I go about finding the total current? Homework Equations See photo above. The Attempt at a Solution See above.[/B]
  9. D

    Exploring Induced Current in a Metal Coil

    Homework Statement The figure shows a metal coil labored as A. Heading torwards a region where a uniform static magnet field exists, poiting torwards the ground (hence X). The coil moves with the same constant velocity. As it enter the magnet field the coil will have an induced current in it...
  10. Benoit

    Eddy current loss in solenoid half-filled with magnetic core

    Hey ! Let's say I have a solenoid that is only half-filled with a magnetic core. Now I want to know what is the loss due to Eddy currents. First, I want to find the magnetic field with Ampere's law. With this kind of geometry, I'm not even able to apply Ampere's Law ! have of picture here of the...
  11. Cocoleia

    Magnetic flux, current and magnetic field confusion

    1. The problem statement Relevant equations: I am confused. When dealing with Ampères law: dl is supposed to be the length element? Like when we have Gauss' law for electric fields and we use a circular Gaussian surface, we have E(4πr^2)=Qenclosed/ε So in this case, when we have a circular...
  12. J

    Why a DC (direct current) component is undesirable?

    When choosing Line Codes (e.g. Bipolar or Polar formats) for transmission of bits over a communication channel such as twisted pairs, it is always desirable that no DC component is present for a particular choice. According to William Stallings (Digital Communication Book) "With a dc component...
  13. S

    Kirchoff's Voltage Law and Current Law --

    Homework Statement Homework Equations Using Loop 1, 2 and 3 The Attempt at a Solution
  14. BrainMan

    Induced Current in a Coil with Changing Magnetic Field

    Homework Statement A 5.0-cm-diameter coil has 20 turns and a resistance of 0.50Ω. A magnetic field perpendicular to the coil is B=0.020t+0.010t^2, where B is in tesla and t is in seconds. Find an expression for the induced current I(t) as a function of time. Homework EquationsThe Attempt at a...
  15. doktorwho

    Question regarding a magnetic field path around a gapped core

    Homework Statement ##l/l_0=100## ##S=3 (cm)^2## ##B_r=200μ_0H_c=2mT## ##R=10Ω## No current runs through the feromagnetic core. Calculate the charge ##q## that goes through ##R## from the moment in the diagram to the moment it is removed from the core. Homework Equations 3. The Attempt at a...
  16. jlmccart03

    Finding frequency of an AC current sin wave?

    Homework Statement An AC current is given by I= 475 sin( 9.43 t), with I in milliamperes and t in milliseconds. Find the frequency. Homework Equations w = 2pi*f The Attempt at a Solution I got 9.43/2pi which is 1.5 Hz, but that is wrong. I honestly have no idea what to do to find the Hz.
  17. V

    Getting the magnetic field as a function of current

    Howdy, So, I'm curious, is there a general relationship between current input into an electromagnetic and the magnetic field that it generates in space? The trivial example is wrapping a wire around a rod, then sending a current through it which causes a magnetic field. My set up is a simple...
  18. A

    Finding the direction of current given a varying magnetic....

    Homework Statement Homework Equations μ0 In,e = ∫B⋅ds The Attempt at a Solution I really don't how to approach this question at all. Do you have to integrate counterclockwise around the loop every time? If the field was decreasing as y decreased, would you integrate CW or is it still CCW...
  19. whatphysics

    Finding closed loop gain and Ip and In current in op amp

    Homework Statement Finding closed loop gain and Ip and In current in op amp Homework Equations - The Attempt at a Solution I started by trying getting voltage divider for points between R1 and R2 as (R2/(R2+R1))Vs and between R4 and R5 similarly. And I'm not sure how to continue on. Any help...
  20. TheBigDig

    Using Nodal Analysis to determine current in a resistor

    Homework Statement Homework Equations ##V = IR## ##\sum_{k = 0}^{n} I_k = 0## The Attempt at a Solution [/B] I set the bottom node as the reference node and worked from there to find the three equations for the loop. When I try to eliminate ##I_4## by using ##I_4 = I_2 - I_3## I run into...
  21. A

    What happens to a coil of wire as current is increased?

    Homework Statement Homework Equations L = (N * F_b) / I (where F_b is the magnetic flux) emf = -L * (dI/dt) The Attempt at a Solution I originally thought that the inductance would decrease since it is inversely proportional to current. But, looking at the equation for emf, that would...
  22. A

    Simple inductance question: Finding steady state current

    Homework Statement Homework Equations I = E / R_total The Attempt at a Solution I mostly just want to clarify that my thinking is correct. The solution for this problem shows that the current is split evenly between the two paths. Is that because we're assuming that the inductor has no...
  23. R

    B Are All Four GW Detectors Currently Operational for Simultaneous Observing?

    The second LIGO observational run started last year and according to Wikipedia the germany and italy based GWs detectors Geo600 and Virgo are already operational, I would like to confirm whether as of now the 4 detectors(2 from LIGO,1 GEO and 1 VIRGO) are simultaneously fully operative. I would...
  24. alfab

    The functional form for dependence of force on Current?

    I am working on a lab where we were measuring how magnetic force between two parallel conductors varies with current and the separation between the two conductors. I need to find a formula for the dependence of Force on current to create a fit line on the data in my graph that shows the relation...
  25. mfb

    I B -> s µµ decays: Current status

    Something curious is going on with these decays. LHCb gives a seminar talk Tuesday next week, a livestream will be available. Edit: See results discussed starting here I'll summarize the current status here. I tried to keep most at the advanced (I)-level, but I don't think that always worked...
  26. jlmccart03

    Find current through inductor after many time constants.

    Homework Statement In the figure, R = 1.9 kΩ and ε0 = 60 V . When the switch is closed, the current through the inductor rises to 10 mA in 30 μs . What will the current in the circuit be after many time constants? Homework Equations I = V/R or I = ε/R if current is constant which after many...
  27. Sevs evans

    Is it possible that there is a 220 volts but low current?

    I read at the power outlet,the meter detect 220 volts but the split type AC doesn't work.it happens when I used the back up generator.
  28. D

    Find output current of NMOS transistor

    Homework Statement Vtn = 0.4V W/L = 10 NMOS1 Saturation Region Drain = 2.5V Gate = 1.9V Source = 0V Vtn = 0.4V W/L = 10 NMOS2 Triode/Linear/Ohmic Region Drain = 0.5V Gate = 2.2V Source = -2.3V tox = 9um un = 250cm^2/V W/L = 10 Homework Equations Saturation: Id = Kn * (Vgs-Vt)^2/2...
  29. Addez123

    Does a wire loops' magnetic field affect it's current?

    When you run current through a circle formed wire it generates a magnetic field. Will this field affect the current in the wire that generates it? I mean if it does wouldn't the calculations for the created magnetic field be rather circular? The magnetic field depends on the current which in...
  30. G

    Does current flow back to the power plant through the ground?

    Hi. I fear I might not have understood some fundamental concepts about electric power transmission. So we have "neutral" which is brought to Earth potential. Does this mean the electrical circuit from the power plant over highly conductive aluminium cables to my home closes back to the power...
  31. S

    Charge passing through a cross section for a time varying current

    Homework Statement The current in a wire varies with time according to the equation I(t) = 6.00 A + (4.80 A/s)t, where t is in seconds. How many coulombs of charge pass a cross section of the wire in the time period between t = 0.00 s and 3.00 s Homework Equations I=dq/dt The Attempt at a...
  32. D

    Simple test using current values to prove polarity

    I work in a large electrical machine shop. We have a test that no one can explain to me. We energise a dc field frame (in this case 6 pole) with ac and record the current draw, then reverse the polarity of connection, energise and compare values. If a pole is reversed polarity then a difference...
  33. B

    Need help with permeability of free space.

    Homework Statement In a lab that I did in Physics we calculated the magnetic field of a solenoid while constantly increasing the number of time the wire was wrapped around the electromagnet. After I obtained all the values, plotted it in a graph and found the line of best fit, the slope came...
  34. S

    Voltage drop and current through each resistor

    Homework Statement Determine the voltage drop and current through each resistor. *This is just my sketch of the problem since I couldn't take a clear picture of it. Homework Equations Ohm's law V= IR Parallel total resistance Req=1/R1+1/R2+1/R3+... Series total resistance Req=R1+R2+R3+...
  35. kookamlok

    Misunderstanding about the choices of current values in KCL

    【Moved from general forum. Homework template is missing.】 By KCL, -ID2 + (-I2) = 0 0 = ID2 + I2 Q1: Do you think this equation is correct? (i assume it is correct because it came from my professor's notes) Q2: Which node do you think this equation is used for making this equation with...
  36. P

    Kinetic energy in ocean current

    Homework Statement Consider an Ocean Current flowing at 2.5 m/s. a) How much energy is contained in a cubical block of water 1m on the side. (The density of the water is about 1030kg/m^3.) b) If the flow is perpendicular to one of the cube faced, what is the rate at which current flow carries...
  37. P

    Electromagnetic induction in current loops

    would be really grateful if someone could help throw some light on this - its probably really simple but I am typing myself up in loops! I have a piece of wire which is placed in an external AC magnetic field which is varying sinusoidally. The wire is folded to make two rings of radii r1 and r2...
  38. P

    Building speakers, induction and induced current

    i made a speaker from a cup, a coil of wire and a magnet. I hooked up both of the ends of the wire to a headphone jack and it works. Albeit very low sound, but it works. Can you point me in the direction of some equations that will show me the most influential factors on how to make it louder...
  39. K

    Electricity, voltage, current, resistance relationship

    Hi, The Circuit I am referring to is a simple series circuit with the resistance of the wire is negligible. I am confused about the fact that if we increase the resistance of a resistor in a circuit, the PD across the component will also increase. From my understanding I thought increasing the...
  40. S

    Solving Magnetic Field & Current Direction Problems

    Homework Statement Two circular coils of diameter 30.0 cm are parallel to each other and have their centers along the same line L but separated by 22.0 cm. When an experimenter views the coils along L, the coil closer to her carries a clockwise current of 2.50 A. Find the magnitude and sense...
  41. S

    Magnetic force on current carrying wire

    Homework Statement A wire along the z-axis carries a current of 6.8 A in the +z direction. Find the magnitude and direction of the force exerted on a 6.1-cm long length of the wire by a uniform magnetic field with magnitude 0.36 T in the -x direction. Homework Equations F=I(LxB) The Attempt...
  42. Manoj Sahu

    Neutral Conductor Current: How is it Possible?

    I read in a book that during normal working condition (balanced system) the current through a neutral conductor is zero i.e., Ia+Ib+Ic =0 where Ia, Ib, Ic are phase current of three different phases a, b, c. How is that possible? I mean if you look at mathematical result of the phases they are...
  43. A

    Synchronous Machine Voltage Curves & Torque Relation to Armature Current

    Hello everyone Im new on the forum and I just discovered what are sync machines... I have really basic question what I still cannot figure out.. I did some experiments with motor for different field currents and torques. In the result I measured armature currents and did V curves. But next...
  44. B

    Circuit that reverses the flow of current to a motor

    Hello, I am building a small car that upon hitting a wall will go backwards, in other words reverse the current flow. I have all the components requiered (resistors 3k and 1k, wires, 6V battery, and an H-bridge, locking button) only thing I do not know is how to connect them all together. If...
  45. Akmalidin

    Constant Current Source for high current

    Hi, I am building a charger for my bicycle front and tail light that uses dynamo to charge them while cycling. However, depending on my speed, current is fed differently to lights and they start to flicker. Therefore, I was wandering if there is a way to make a constant current source which...
  46. Kelsi_Jade

    Find the Current Flowing through each resistor

    Homework Statement Homework Equations / 3. The Attempt at a Solution Looking to solve mistakes to study from homework. Here's what I had so far[/B]
  47. M

    Calculate the temperature of a wire as an electrical current flows through it

    Hey, so I'm just wondering what are the formulas needed to calculate the temperature of a wire after x amount of time as an electrical current is passed through it. I know how to solve for it... I just forgot the formulas. Thanks
  48. Vanessa Avila

    Finding the current through the battery

    Homework Statement I am confused what to do but I have to find the current through the battery: Homework Equations V=IR The Attempt at a Solution I decided to find the equivalent resistance and do V/R = I using the 14V, but I believe my Req is wrong. What is throwing me off is the...
  49. S

    Would current flow in a vacuum like space

    Would lightning work in space? I think it would but you wouldn't be able to see it? Let's say I have some sort of device that creates a lightning bolt, if I shot it at a watermelon in a vacuum or another target would it hit the target, or nothing happen because of the vacuum?
  50. G

    Current at Extreme Frequencies

    A work colleague of mine told me that if you have an AC voltage across a wire and the frequency is high enough, there would not be any current, because electrons don't have time to move from one atom from another. Is there any truth behind this?
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