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. 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?
  2. D

    Harmonic Distortion in a current waveform

    Homework Statement [/B] Estimate the total harmonic distortion [THD] present in the current waveform using the formula: Homework Equations ##THD\left(I\right)=\frac{1}{I1}\sqrt{\sum_{n=2}^\max\left(In\right)^2}\times 100\%## The Attempt at a Solution I have attached a worksheet for this. The...
  3. J

    I Positron/Proton Scattering Weak Charged Current

    Hello, I'm wondering how you would go about drawing a Feynman diagram for a weak charged current scattering interaction of a positron and a proton. I have attached a diagram of what I have tried but it doesn't conserve lepton number (I think this is a problem, from what I gather...
  4. S

    AC Current in GHz Frequency and Zero Resistance

    Hello Experts, I am a physics newbie with big ideas. I have a question. I am thinking about how to produce a zero Resistance Current. We know we can do this using super-conductors in sub zero temperature, but maybe there's another way. My assumptions (which could be wrong): 1) Resistance in a...
  5. jlmccart03

    Find loop radius and current via magnetic field?

    Homework Statement A single-turn wire loop produces a magnetic field of 41.2 μT at its center, and 5.15 nT on its axis, at 20.0 cm from the loop center. Find loop raidus and current. Homework Equations F = qv x BThe Attempt at a Solution I tried to use the above equation, but could not figure...
  6. B

    Conceptual Understanding for Voltage in a Circuit

    I'm having trouble understanding circuits, particularly voltage. So my question is more of a conceptual dilemma. Please correct my definitions and relations if it is incorrect. Voltage is the energy provided per charge, and this energy is converted to KE once the circuit is closed, or in other...
  7. J

    Possibility that all current interpretations of QM are wrong

    Is there a possibility that none of the current interpretations of QM are right? Or is the current interpretations all that there will be on the table?
  8. D

    RC Multiloop Circuits, Find Current at Specific Time

    Homework Statement Homework Equations For a basic RC circuit during charging: q = CV(1-e-t/RC) i = V/R (e-t/RC) The Attempt at a Solution I can solve basic RC circuits but this is just out of my realm of understanding. I can also find the max charge of the capacitor. I'm not looking for...
  9. D

    Finding general expression for probability current.

    The conservation of probability says: $$\partial_t J^{0} + \partial{i}J^{i} = 0$$ Use the Schrodinger equation to obtain$$ J^{i} (\vec r)$$. I have no idea where to start this kind of problem because the notation makes no sense to me. I would appreciate a hint or nudge in the correct direction.
  10. P

    Find currents I1 and I2 in a 3-loop, 2-battery circuit

    Homework Statement Find currents I1 and I2 in the following circuit: Homework Equations I know I have to use Kirchoff's loop rule but I am not sure of the current going through the 5 ohm and 8 ohm resistors, is it just I1 and I2 respectively? Also do I incorporate the large loop at the...
  11. V

    Finding net magnetic field?

    A long horizontal wire carries 22.0A of current due north. What is the net magnetic field 20.0 cm due west of the wire if the Earth's field there points downward, 40 degrees below the horizontal, and has magnitude 5.0 E-5 T? My approach: 1. Drew north to the right and the wire lying flat, with...
  12. BAJ

    Parallel circuit of current sources

    Assume I have a parallel circuit of current sources with 5 current sources generating 1mA each. Therefore from both the terminals I will get 5mA total. Now if I add a battery to one of the terminals where current(i) will flow into my circuit. If i = 50mA, will I get 55mA current from another...
  13. S

    A question for mathematicians or current math PhD students

    Hi everyone. I wanted to pose this question to those who are currently working as mathematicians (faculty members or postdocs, or those who finished their PhD and are working in industry), or current PhD students in math. Did you double major in mathematics and physics in your undergraduate...
  14. Mind----Blown

    Surface current density-logic and definition contradict

    Okay, so in Griffith's introduction to electrodynamics, Griffith clearly defines surface current density as follows: "when charge flows over a surface, we describe it by the surface current density, K. Consider a 'ribbon' of infinitesimal width dL running parallel to the current flow. If the...
  15. I

    B How to remember what happens to I, V and R in a circuit?

    There are two circuits, each consist of a cell and two bulbs, in one circuit they are in parallel, and in the other they are in series. What's the best way to remember which lamp has the greatest pd, current and resistance when one bulb is brighter than the other in the series and parallel circuit?
  16. Peter Andrews

    Finding displacement current in an AC capacitor circuit

    Homework Statement A capacitor is made of two parallel plates of area A, separation d. It is being charged by an AC source. Show that the displacement current inside the capacitor is the same as the conduction current. Homework Equations Idisp = ε(dΦE/dt) Q = CV C = Aε/d Xc = 1/(2πƒC) Q(t)...
  17. D

    Engineering Finding the Total Force on the Circuit Loop

    Homework Statement The problem asks to find the Total Force on the Circuit Loop. I have a circuit loop with length 30.0 cm and width 10.0 cm with a current I2= 30.0 A that is flowing counter-clockwise. There is a wire that has the current I1=15.0 A flowing from left to right and is 7.50 cm from...
  18. T

    EM Induction:current in one coil inducing current in another

    Homework Statement Two coils P and Q are placed close to one another, as shown in the first figure attached. The current in coil P is now varied as shown in the second figure. Show the variation with time of the reading of the voltmeter connected to coil Q for time t = 0 to time t = t 2...
  19. M

    Current of RC Circuit After Switch is Opened

    Homework Statement See attached image for circuit diagram and givens. The switch has been closed for a very long time. a) What is the charge on the capacitor? b) The switch is opened at t=0 s. What current initially flows? Homework Equations V = IR Q=CV I=I0e-t/(RC) The Attempt at a Solution...
  20. P

    What is the value of I3 for the given line integral and values of I2 and B?

    Homework Statement The value of the line integral around the closed path in the figure is 1.79×10−5 Tm . https://session.masteringphysics.com/problemAsset/1385538/4/32-22.jpg There is I2 and I3 inside the closed loop. I2 = 12 A What is I3? Homework Equations Amphere's Law: B = Uo I(enclosed)...
  21. S

    Physics Current Outlook for Medical Physics?

    Hi all, I'm a current full-time employee in a calibration laboratory with a b.s. in applied physics. I see in my current position there is a ceiling for career opportunities and am looking to return to school for my masters. I feel that I would enjoy the clinical side of things, I consider...
  22. clamatoman

    Solving for RMS current of a resistor, help?

    Homework Statement A resistor connected across an AC power supply has a current given by I=(1.35A)cos(300t) when connected to a power supply with emf 120 V rms. Find the RMS current. Homework Equations IRMS=Imax/√2 The Attempt at a Solution IRMS=Imax/√2 IRMS=0.477 A INCORRECT Not exactly sure...
  23. A

    Finding expression for the current

    < Mentor Note -- thread moved to HH from the technical forums, so no HH Template is shown > Hi all, I'm trying to find an expression for the current i(t) as a function of C and V_out (t) after t = 0. I have an answer but still not sure at all if its correct or not. Here is my answer: I know...
  24. Asmaa Mohammad

    The relationship of the current before and after a change.

    Homework Statement An AC source was connected to a capacitor and an inductor (ignoring its ohmic resistance) in series. If the inductive reactance was equal to twice the capacitive reactance, and then the frequency duplicated, determine: 1. the relationship between the the current before and...
  25. G

    Autotransformer: Why does primary current go through coil?

    Hi. Why is it that in an autotransformer apparently most of the primary current goes through the winding and not through the load?
  26. chikou24i

    Pulse current discharge test of a Li-ion

    Could someone please explain to me what is the definition of a pulse current discharge, and what do we mean by pulse current discharge test ?
  27. G

    Can EMF be the same as the current (const)?

    As the title states, can EMF = I = const ?
  28. B

    AC current / circuit simulation software

    I'm looking for software that can simulate an ac circuit. After a quick google, I found several free online services (which I will try out). What I was wondering though is if anyone had some advice concerning my selection. A brief list of requirements: accurate simulation of different conductor...
  29. B

    Voltage & Current & Push & Force & Potential

    Homework Statement I’m trying to understand what voltage is. Getting confused. I've written my confusion as questions below and answered the questions. (i) What is voltage? (ii) What is voltage passing through a lightbulb? (iii) Is POTENTIAL just another...
  30. terryds

    Current as a function of time in an RC circuit

    Homework Statement How to determine the current as a function of time that flows in 10 ohm resistor, 100 ohm resistor, and 15 microFarad capacitor? Please help Homework Equations I = V/R I_capacitor = I e^(-t/RC) The Attempt at a Solution I only know the equation V=IR and the capacitor...
  31. A

    Why does the current take this path?

    Homework Statement (see attached file) Homework Equations Kirchhoff's laws The Attempt at a Solution (see attached file) I only included the work for measurement 1 since measurement 2 follows from that. I got both voltage values correct. However the paths of the current flow was incorrect...
  32. M

    How to Calculate the X-Component of the Magnetic Moment in a Rectangular Loop?

    Homework Statement A rectangular loop of wire with sides H = 22 cm and W = 77 cm is located in a region containing a constant magnetic field B = 0.82 T that is aligned with the positive y-axis as shown. The loop carries current I = 334 mA. The plane of the loop is inclined at an angle θ = 30°...
  33. D

    Programs What Are Current Issues Whose Answers Lie in Physics?

    I have decided that I want to pursue a career in physics and chemistry. It is very important to me that my career helps people. While I know that there are current testing and research being done for cures and treatments to numerous diseases, I don' think that biology is the field for me. Thus I...
  34. miguelcard

    Engineering Finding Current in a Thevenin Circuit

    Homework Statement Given a circuit with a total of 3 sources , 2 Voltage sources and 2 Current sources and 4 resostors, Find the Cirrent I2 passing through the branch where R2 and V2 are. And I am asked to give the formula for the value of the voltage in the current source. Attached the...
  35. I

    Why does the current need to be small when using an ohmmeter?

    Homework Statement The question wants to know why th current should be small through a wire when using an ohmmeter. Homework Equations None The Attempt at a Solution I can't think of a solution, and looking online doesn't give any answer.
  36. B

    Confused about voltage & current -- Please check my understanding

    Hello, This is not a homework but I’m confused about current and voltage. My understanding is fragile and I need to reinforce it with your help. Below I’ve written what I think I know to be correct. Please correct me where required. This is high school physics.(i) Current is the...
  37. G

    Magnetic flux and current directions of transformer

    Hello. Let's take a transformer picture first. The basic equation explaining how the transformer work is the equation of Faraday's law of induction. \begin{array}{*{20}{c}} {{V_P} = - {N_P}\frac{{d{{\rm{\Phi }}_B}}}{{dt}}\;\;\;\;\left( 1 \right).}\\ {{V_S} = - {N_S}\frac{{d{{\rm{\Phi...
  38. Bassa

    Initial Voltage in an RC circuit with a Current Source and no Voltage Source

    Homework Statement [/B] Derive an expression for vc(t) in the circuit of Figure P4.13 and sketch vc(t) to scale versus. I attached a screen shot of the circuit for this problem. time. Homework Equations V = IR V = V0exp(-t/tau) The Attempt at a Solution [/B] I am trying to find the...
  39. whatphysics

    Finding the forward current of diode

    Homework Statement A Si diode is operated at the room temperature (27 °C). For a forward current of 1 mA, the voltage VD is found to be 0.9 V. If the VD is 1 V, the forward current = _____ mA. Given that nVT = 26 mV The answer is 46.81 Homework Equations Shockley diode equation? The Attempt...
  40. U

    Which is better -- amp ground connected to frame or battery?

    There is this debate in car audio forums of this question whether it is better to connect your amp ground to the frame of the car or the battery.. basically they haven't came to a conclusion so I was curious what you guys think... Basically what I mean is that when you hook up an amp in the...
  41. Hamood97

    Find the two figures and the get value of the resistor and current

    Homework Statement finding the resistor and current which is following through the circuit[/B]Homework Equations kirchhoff law The Attempt at a Solution almost as fig 1 ( 9v=3.458 mA and 12v=11.122 mA) fig 2 (9v=1.472 mA and 12v=12.882 mA) i3=2.48 mA
  42. Asmaa Mohammad

    RLC Circuit Behavior with Changing Frequency, Capacitance, and Voltage

    Homework Statement In the tuned circuit below, what will happen to the reading of the ammeter when: a) source frequency increases. The voltage is constant b) the capacitance increases. The voltage and source frequency are constant c) The voltage increases. Source frequency is constant...
  43. nagyn

    Current through left bridge of a Wheatstone Bridge

    Homework Statement The ammeter in the Wheatstone bridge of (Figure 1) measures zero current when the resistance Rvar of the variable resistor is set to 189 Ω . What is the current IL through the left side of the bridge? Homework Equations Junction rule: ILeft + IRight = I4 I4 + I2 = I1...
  44. Y

    Calculate collector current of phototransistor

    Hello, I'm wondering if it is possible to calculate current the collector current of a phototransistor that is paired with an IR Led? I have an IR Led that is 13.6 cm away from the phototransistor and has a radiant intensity of between 65 mw/sr and 125 mw/sr. The phototransistor that I'm...
  45. solour

    Current Through A Resistor That Is In Parallel With A Capacitor

    Homework Statement [/B] My question is regarding part C of the question. Homework Equations V = IR V(t) = V(1-e^(-t/tau)) The Attempt at a Solution My idea is to use Kirchoff's Voltage Law and find the voltage of the capacitor as a function of time, then since the voltage across capacitor is...
  46. K

    Induced current in a moving bar on rails

    Homework Statement 2 movable conducting bars on a conducting rail with a uniform magnetic field heading inside the paper , what will happen to bar 2 if we move bar 1 to the left with a velocity v ? 3. The Attempt at a Solution i think that a current will be induced in bar 2 and pass to bar...
  47. Arup Biswas

    Good books for learning AC current?

    I'm a 2nd year Physics student! I want to learn electricity from it's absolute basics! Like AC current, how it is formed, where is formed etc. Please suggest me books which will tell me about the theory in details along with required mathematics too!
  48. I

    How to find Voltages and currents of the following circuit

    Homework Statement The circuit of the given problem is attached to this post (jpg file). All info is given in the photo. Problem: find VA, VB, IA. Homework Equations Ohms law KCL equations P = VI or V^2/R The Attempt at a Solution - First, I noted that VB = 9 - VA. - next, i set up a KCL...
  49. W

    Current through a conductor with varying cross-sectional area

    Homework Statement Homework Equations I = nqVA J = E/ρ J = I/A The Attempt at a Solution The underlying assumption was that current was constant across all 3 bits of the conductor, and thus answer is b. The concept I can't grasp is this: Why is current constant? Shouldn't a smaller A mean...
  50. L

    Induced current in a metal ring

    Homework Statement A metal ring with a radius of 10cm and resistance 0.1Ω passes through a delimited magnetic field, look at the photo posted below. The ring has a velocity of 5m/s, and the magnetic field has the field strength 0.4T. When the ring passes through the magnetic field, at some...
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