What is Current flow: Definition and 137 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. Understanding Inductance and Induced EMF in Simple Circuits

(a) ##\displaystyle\mathcal E=-L\frac{di}{dt}## = -0.260 x -0.0180 = 0.00468 V = 4.68 mV (b) Current always flows from higher potential to lower potential. So, b is at a higher potential. My textbook says that my answer for part (a) is correct but part (b) is wrong. Please help!
2. Propagation speed and LC model of transmission line

I am a bit confused on the speed of voltage propagation in the transmission line and I hope someone can enlighten me. I understand the speed of voltage propagation is in the same order as the speed of light and it is much faster than current. But if we can model the transmission line with a...
3. I have a question about diodes and the PN junction

Is the PN junction inside a diode what makes the electrical current only flow in one direction and not in the opposite direction? If this is so, why does it happen? Also Why is the P-type material said to have empty holes and the N-type material to have free electrons?
4. B Where Do Electrons Go When a Battery Loses Charge?

I am no physicist or student and am asking question in order to out try and understand why my old tractor is not charging. This got me into understanding the concepts of how the generator and voltage regulator work to create a current to charge the battery. My investigations pulled me down in...
5. Battery circuit current flow when charging

I would like to know when a alternator is charging a battery is the current flow a series opposing circuit......?
6. I Can current flow in an open circuit?

I have two related but separated questions: 1. If I have an open circuit connected to a battery, let's say an alkaline battery connected to a straight wire and nothing more, once I connect the battery to this wire there will be for a short time a current in the wire? Since in the battery due to...
7. 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...
8. In what way does current flow through a potentiometer?

Above is a picture of a potentiometer with terminals A, B, and W. Does current always from from A to W or can current flow directly from A to B? Is there usually both? And what do they mean when they say a potentiometer is an effective "voltage divider"?

N/A
10. 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...
11. When current flow reach indeterminate form

Homework Statement If the current flow, in a branch of a circuit, is a function of say (√(x + 2)-2)/(x-2) (or any such that give an indeterminate form at a certain value) of an input source current x. What current will be flowing on that part of the circuit, when the function become...
12. Current Flow Through Lamps in Circuits

Homework Statement [/B] State and explain whether or not current will flow through the lamps in these circuits Homework Equations None The Attempt at a Solution I am confused with figure 6 as my explanation is different from my textbook's answer. My textbook says: "Figure 6 – the lamp is...
13. B LC Oscillation: Current Flow & Charge Polarity

when in LC oscillation current flow from inductance to capacitor and charge is opposite polarity. why don't current flow in reverse of it and charging the capacitor in same manner as it was earlier.
14. Why does a resistive wire heat up from current flow?

The kinetic energy of electrons in a conductor is roughly 9 orders of magnitude greater than the kinetic energy from the drift velocity of the electrons. It seems that the kinetic energy from the drift velocity is not enough to account for the heating, where does the heat energy come from? Cheers
15. Current Flow Through a Common Part of a Circuit (batteries and light bulbs)

Hello, I have a simple question regarding current flow through a common part of a circuit. I encountered this as I am reading "Code: The Hidden Langauge of Computer Hardware and Software" by Charles Petzold. The images I've attached display what I'm talking about. I'd like to know if there's a...
16. In which direction does the current flow?

Homework Statement We bind two batteries with voltage 2V and 1.7V with inner resistance 0.2Ω and 0.1Ω in parallel series in such way that we bind each positive poles and negative poles together. What current runs trough the circle? What is the voltage between contact points of the batteries...
17. Find the current induced in a wire loop by a nearby current

Homework Statement Homework EquationsThe Attempt at a Solution When the circuit moves creates magnetic force that moves the some charges in the wire and that is a current. That is what i thought. F = Q.v B sin theta B = ( permeability Of vacuum* I)/(2pi.r) But how to find the I? Thank you...
18. What's the current from this circuit? Is it a short circuit or not?

Homework Statement Pic A, what's the I2? Pic B, what's the current across a-b ? Homework Equations V = I*R Voltage in series is different, the current is the same Current in parallel is different, the voltage is the same The Attempt at a Solution from Pic A, I found that I1 = 1A, I3 = 1A...
19. T

How does a resistor exactly reduce current flow in a circuit

Greeting . It is clear to me that the resistor represents a physical obstruction to the passing current I do not know how exactly it works and I will try to show what I was really interested in the diagram.
20. Understanding Linear Motors: Right Hand Rule & Current Flow

Hi there, I attached an image of a basic linear motor. I'm a little confused if I use the right hand rule or left hand rule. I did it both ways and I think the left hand rule is the only rule that allows for a force being applied to the right. I assume the current is going down rather than...
21. Current flow in a two source circuit

Hi guys, is the current flow in this picture correct? I'm trying to understand current flow in a two source circuit.
22. D

Temperature related to Current flow on BBr or cables

Temperature with hot spot by Ir thermal cameras of modern development is being used for measuring on the object of terminal surfaces and cable working temperatures in particular working loads. However, so far no measurements has been designed to obtain the result on the flow of current...
23. Capacitor - why does current flow

I have question, why can condesator get charged, when connected to voltage source, if for current to flow, there most be closed wire, but here it is not, but there still is current? Thanx for answers.
24. Current flow on the surface of a permeability bigger than 1

Hi, Quick description of the problem at hand: spherical perfect conductor around the origin with radius a, spherical shell (with radius b) around it made of a material with given magnetic permeability bigger than 1. Uniform Magnetic field in the area. The solution I am looking at (which I won't...
25. How does electric current flow through a conductor

There's been a discussion going on since this following thread: Range of frequency of electromagnetic wave how electric current flow through a conductor. I need a proper clarity, does the electrons literally displace and flow or just the disturbance/energy travel through conductor making...
26. 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...
27. 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?
28. Current flow direction in "infinite" cube of 1ohm resistors

Homework Statement Write a program to find the equivalent resistance between two opposite corners within a grid of "infinite size" with resistors between each point. So basically we have an infinite cube made up of cubes with 1 ohm resistors between each node. Homework Equations Kirkoff's laws...
29. Resistance calculation on right angle current flow

As you know, resistance of a rectangular shape is given by R=ρ A/L But how do we theoretically calculate the resistance of the bottom case? ( now, the current flow is not parrallel, current flows from bottom through the right side) I would like to know if there is any references for this...
30. Direction of current flow in KCL/Node Voltage Confusion

Homework Statement ------------------ Homework Equations V=IR KCL/Node Voltage The Attempt at a Solution These are the solutions to some old homework assignments that my teacher posted, but I am very confused on the way he labeled his current flows in these problems. In the first picture...
31. Current flow model through a resistance field

Hey everyone. I thought about this problem the other day, but I don't know what theory I need to solve this problem. Given a 2D rectangle with a known, varying resistance, and a known voltage drop across the length, how would one calculate the current density at each point on the surface. By...
32. About capacitor -- how can current flow "through" it?

Usually people get kind of frustrated about how can a capacitor charge up when there's no current flowing through, including me. Can I interpret the picture better by considering the electric potential set up by the battery across the circuit? Is this interpretation a correct one? Sorry for...
33. Detecting Current Flow in a Circuit with LEDs

I am desgning a circuit(network), where i need to show the path traversed by the greater part of the current at each node, consecutively. using an ammeter (or voltmeter) in every branch (around 20) makes it too tedious. Will LEDs do the required work? But they would light up at all locations...
34. Circuit Problem -- With only a battery in the circuit, will current flow?

Homework Statement Will current flow in an ideal circuit given that there is only an ideal battery in the circuit? Homework Equations V=IR The Attempt at a Solution Since there is no resistance through out the circuit no potential is dropped so no current flows
35. Neutral Wire Current Direction and Magnitude in AC Power Distribution

What determines the direction of current flow through the neutral wire? What determines the value of the current through the neutral wire?
36. Skin effect and magnetic field of a flattened conductor?

A conductor with a large high frequency AC current causes a "Skin Effect" meaning that most of the current flows at the surface of the conductor. What does the skin effect look like if you have a conductor with one side flattened? And what does the resulting magnetic field look like? See...
37. A Fermi energy Ef changes with applied electric field?

Hi people, I don't understand why when we apply the electric field to the metal Ef remains the same. Ef as translation energy of electrons remains the same but we accelerate the electrons with applied electric field so the translation energy increases too? In other hand according the formula...
38. Current flow across inductors in Series

I can't articulately ask the question so I drew a diagram. In the diagram, both capacitors are equal in capacitance. The bottom inductors are both 10000 nh and the top are 100 nh. A. Will the capacitors charge at the same time? B If we switch the large inductors to the top and the small to the...
39. Increasing current drawn in Arduino Motor Shield

I am currently using the Adafruit Motor Shield in conjunction with an Arduino Motor Shield to control two 7.2V DC Motors. The DC Motors are being powered by a 7.2V, 3000 mAh Nimh battery. When the two DC Motors are being powered in parallel directly by the Nimh battery, they are able to move...
40. Calculate the required current flow in the suspended wire

Homework Statement In the figure, the top wire is 1.5 mm diameter copper wire and is suspended in air due to the two magnetic forces from the bottom two wires. The current flow through the two bottom wires is 70 A in each. Calculate the required current flow in the suspended wire. Homework...
41. Help with current flow, voltage, resistors in basic circuit

Im reading this stack exchange question: http://electronics.stackexchange.com/questions/28897/how-to-choose-value-of-resistor-in-voltage-divider So there is a 5V circuit with 2-100 Ohm resistors that yields a voltage drop across the divide of 2.5V. The current through the circuit is 25mA...
42. Trouble understanding - to + vs + to - current flow

Homework Statement When reading about directions of magnetic flux in relation to current flow on pages 6 to 8 of http://www.free-energy-info.tuks.nl/Non-Ferrous-Magnet.pdf , I found that in figure 11 the current is traveling from + to - terminals, while in figure 12, the current flows from - to...
43. Does current flow in both wires or in one in our homes?

If we have a source of AC current with two terminals ( A and B ). We connect a device with this source. Now we say that one wire is live and other is neutral. But my question is that, how one wire is neutral. As we say that in AC current the terminals change the polarity. Its mean that some...
44. PN Junction: Current flow in Reverse Bias

Can someone explain why after a certain voltage, current flows. We were taught that in pn junction when a reverse voltage is applied the depletion region grows wider. Using this no matter what the voltage current should not increase. So why does a current flow when a reverse current is applied.
45. Trying to understand the finer points of current flow

I'm looking at an ungounded 3-phase system here for starters. In a perfectly ungrounded system, grabbing a phase seems safe in theory, but in practice (because perfect ungrounded doesn't exist), this is a bad idea. I'm trying to determine exactly WHY. If I have a perfect ungrounded system...
46. Ion Flow Through a Channel: Current and Charge

Sodium ion flows a through a cylindrical ion channel --> diameter = 0.85 um and is 5 um long. potential difference b/w the ends of the channel is 225 mV drift velocity = 0.015 m/s in a period of 1 ms, a total of 15*10^6 ions exit the channel a. total charge exiting the channel in 1 ms =? b...
47. Does any current flow in reverse PN junction?

Homework Statement Homework Equations [/B] When a diode is reverse biased positive donor ions are left in the N semiconductor and negative acceptor ions in the P type. And since the N is conected to + and its donnor ions has a large +charge, why no electrons from P cannot cross the junction and...
48. Boundary conditions for 3d current flow through water

I've forgotten a lot of field theory so I've been rereading it in a couple of electric field theory textbooks. What seems like a simple problem falls between the cracks. I hope some readers can help - it will be appreciated. My application seems simple (solution will require numerical FEA but...
49. Question about current flow and diode?

Ok, I'm trying to simulate a circuit containing a diode and I am a bit confused. I thought the arrow direction on the diode symbol shows which direction the current is able to flow through it. However, in my simulation, it is showing that the diode is limiting current flow in the exact...
50. Current flow in semiconductors

I have big trouble understanding how current flows in semiconductors. As i have understood it it has to do with "valence" and "conduction" bands. I see valence bands as an discrete energy level within an atom that are possessed by electrons. These electrons do not contribute to a net current...