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Questions tagged [electric-current]

A measure of the rate at which electric charge is transported (especially through a circuit), it has units of charge/time.

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How cell drives electrons to flow in a metal wire?

This was my approach using some facts I'd known- At cathode and anode of a cell reactions take place making positive terminal positively charged and negative terminal negatively charged I.e. there are ...
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Do $\rho$ and $\vec j$ change in a moving frame?

Consider a cylindrical symmetrical infinite wire with radius $R$. The wire has constant charge density $\rho$ and current density $\vec j$ (pointing to the right). This is measured from the stationary ...
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Special relativity when observer is traveling with the electrons creating current

There was a situation that has completely baffled me. I<-- -----wire----- q Essentially there are 3 things going on. Positive Charge: Below the wire ...
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23 views

Electric potential due to a current source - Basic equations

In my book I found the folowing formula of the electric potential generated by a current source: $$ \Phi = \frac{I}{4 \pi \sigma} \frac{1}{r} $$ where I is the current, $\sigma$ the electrical ...
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Supermash Voltage Quesiton [closed]

I need to find the voltage on Va.I tried supermesh but nothing seems balancing the equations.Any ideas? 0.4+(0.2-a).1+(0.2-b).1=0 a-b=0.4 (a-0.2).1+a.1+(b-0.2).1+b.1=0
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Induced Currents in Circuits

I was given the following question:- The plane figures shown are located in a uniform magnetic field directed away from the reader and diminishing. The direction of current induced in the loops is ...
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2k views

Watts vs. volts amperes

What I understand: In simple DC circuits, this is a product of the current and voltage, such that 1 watt = 1 ampere x 1 volt I understand that a watt is a unit of power (change in energy per unit ...
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How does electric current continue to flow in a circuit despite there being zero potential difference?

Consider a conductor connected to a battery by conducting wires. When wires are connected then after a very small amount of time steady state is achieved and voltage across conductor becomes equal to ...
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Determining current in a branch having no resistor

In context to the diagram below , it is quite easy to find the current flowing through section AD , which turns out to be 2A , however , I cannot determine the current in any other branches with ...
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Can current travel backwards? [closed]

This is not a homework problem. I posted this specific question as it would be easy for me to explain. If a current flows through the wire it encounters a short circuit 1 and after travelling through ...
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89 views

Why can't free electron flow in water to conduct electricity?

This question is related to how batteries work. In a battery, the electrons can only flow in conductors, because they can't flow in the solution. my own thoughts on the matter: I believe it is ...
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3answers
131 views

How to show that the electrons responsible for a current have an energy within $k_BT$ of the Fermi energy?

It is commonly written in textbooks that in metals the electrons responsible for an electric current are the ones that have an energy about $E_F$ and a few $k_BT$ around that energy. See for example ...
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Current when capacitor and resistor placed in parallel?

If the question is too long please comment to shorten it atleast , I really need an answer. I have just started learning about RC circuits and these circuits are confusing me.My questions-1)What will ...
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1answer
57 views

What forces are acting on electron in a circuit? Do electrons act on each other in a current?

What forces are acting on electron in a circuit? What is the source of such kind of forces? Do electrons act on each other in electric current? If i have an ordinary electric circuit with only one ...
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28 views

Question about the purpose of a transistor [closed]

I've been studying about diodes and transistors and something made me wonder about the purpose of transistors. In the examples we were talking about increasing current by using two batteries with a ...
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Connecting one lead of capacitor to a certain charged object (to get a potential difference)

Setup-A charged sphere , connected to one plate of capacitor , other lead of capacitor is free. Question-Will the capacitor plates go through a charge redistribution ? Arguments/Counterarguments-I ...
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Is a complete circuit required for capacitors to redistribute charges?

Suppose I have two capacitors of different capacitance $C_1$, $C_2$and they have been charged prior connecting by voltage of $V_1$ and $V_2$ respectively the positive plate of one capacitor is ...
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Physical Relation in Maxwells Equations of quantity between as well as fundamental forces

Recently learnt about Maxwells Equations, am wondering what is the physical relation between electric field E and magnetic field B. It would help if the physical meanings are related to the ...
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one terminal of battery connected to opposite terminal of identical battery

I have read almost all answers on PSE and ESE but none of them are to the point or maybe I am not understanding.I have described the setup in the title , I just want to know what will happen , will ...
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Current direction in an electric circuit

in the picture, in the circuit 1, we can see the conventional current direction in the cirucit 2, we can see the real electrons direction it is right i think. but then i have a big problem, during ...
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How to use energy conservation in following case [duplicate]

A capacitor of capacitance C is intially uncharged is connected with a battery of emf ε.Find the heat dissipated in the circuit during charging?How can we apply energy conservation although there are ...
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2answers
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Does current flow in the wire when only one terminal of the battery is earthed?

Let me specify beforehand that this question has been asked previously but I haven't been able to satisfy my curiosity.I know a battery maintains a potential difference between it's terminals , let's ...
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1answer
30 views

Work done in moving a charge in circuit?

Why is the work done in moving a charge from one point to another in a circuit through any path the same even though heat and other losses are there?
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4answers
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Confusion about electron flow and current

So, I learned in class that current is defined as positive charges moving from south to north. However, in all reality, the negative charges are moving, but the convention of positive to negative wors ...
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1answer
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How can the Neutral wire be 0V if its AC? [duplicate]

So I understand Alternating current like a battery, in which the Poles are constantly changed out, so the circuit stays completed, but the electrons change directions. But how can then in an AC plug ...
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1answer
45 views

Is there even a slight transient current when a piece of wire is connected to a single terminal of a cell?

Suppose I have a cell/battery , both the terminals are at non-zero potentials.If I connect a piece of wire to say the negative terminal will there be some sort of electron redistribution in the wire. ...
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Isn't Kirchhoff's junction law a violation of conservation of charge?

As a beginner of classical electrodynamics I am quite confused in understanding Kirchhoff's junction law or it may be the reason that I misunderstood the law of conservation of charge.Please correct ...
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If current through a resistor is zero, does the circuit break?

I'm really confused. I'm studying about how capacitors are charged, and I learnt that there's a resistor attached in series with the capacitor when it is being charged. When the capacitor is fully ...
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3answers
64 views

Charging capacitor in an incomplete circuit [closed]

I have 2 confused questions regarding the below circuit. please help me out How will the capacitor even charge in the following scenario when the right side of the capacitor is not connected to ...
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31 views

Question about current density

I was looking at past exam papers and found a question that I can't understand. It is basically about current flow but the diagram is really confusing me. The diagram is the following: The question ...
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0answers
51 views

Proof of Ohm's Law [duplicate]

I was watching MIT OCW 802 and the lecturer mentioned that Ohm's law has a proof by quantum mechanics. Can someone please explain this.
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What is the current in a short linear antenna in an alternating $E$-field?

Consider a short linear wire with some low but non-zero resistance, such as a copper wire. If this wire is then placed in an alternating electric field that is oriented parallel to the wire, the field ...
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3answers
12k views

Will the volt, ampere, ohm or other electrical units change on May 20th, 2019? [duplicate]

When watching a video by Veritasium about the SI units redefinition (5:29), a claim that the volt and unit of resistance (presumably the ohm) will change by about 1 part in 10 million caught my ...
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47 views

Evaporating tungsten wire

Consider an incandescent bulb having a thin filament of tungsten that is heated to high temperature by passing an electric current. The hot filament emits black-body radiation. The filament is ...
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1answer
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What is the cause of resistance?

I searched for this question on the internet but didn't got a satisfactory explanation. What I thought on the topic is that the cause of resistance is 'the effective nuclear charge'. The nucleus ...
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3answers
44 views

Current Divider rule

If you have two resistors $R_{A},R_{B}$ connected in parallel with a battery, you can find the current that flows through one resistor ex.$R_{A}$ using the current divider rule: $$I_{A}=\frac{V_{T}}{...
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How does resistance affect the voltage drop? [closed]

There is a series curcuit and there are 5 resistors in it which are the light bulbs. I know that current is directly proportional to the voltage and inversely proportional to the resistance. Can ...
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1answer
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Induced EMF in an inductor

In the above figure, the circuit is closed for a very long time and is then opened. It is stated that "the emf across the inductor just after opening will be very high so as to oppose the change of ...
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Thermal Energy in a Conductor

We know that thermal energy developed in a current-carrying resistor is given by $U=I^2Rt$ and also $U=VIt$. So my question is- Should we say that $U$ is proportional to $I$ or $I^2$
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Intuitively, why is the net current through a volume $0$ if the current is steady?

Say I want to find the total current passing through the following volume, provided by Griffiths' textbook on Electromagnetism. It's not the most useful image, but perhaps imagine the inner curved ...
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What is the Electron Flow in a wire with 2 power sources 180 out of phase?

If you took two independent power supplies and set them to a sine with each power 180 degrees out of phase. The powers supplies will share a common line and the load will be equal_____________? Do ...
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Direction of the current and the electrons [duplicate]

If the electric current is defined as Coulomb/second, why is the direction of the current is just the opposite of the direction of the flow of electrons?
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At null temperature (0 Kelvin), is the current going through a diode (PN junction) null?

At null temperature (0 Kelvin), is the current going through a diode (PN junction) is null, for a positive voltage in a direct polarisation, above the built-in voltage of the depleted region ? If ...
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2answers
49 views

What should be the independent variable in a resistance experiment?

I was asked a question by a student today and I have been pondering about it for a while now. In an experiment to measure resistance of a conductor, should we vary voltage across the conductor and ...
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3answers
110 views

Why is a net flow of positive charge in one direction equivalent to a net flow of negative charge in the opposite direction?

If I understand correctly, conventional current was defined with reference to positive charges because it was found that a negative charge flowing in one direction is actually equivalent to the same ...
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1answer
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How does the $I$-$V$ curve for bulk metal look like?

For semiconductors, the current (I) vs. voltage (V) relationship is as shown in the picture below. As we increase the applied voltage, the electron-hole pairs generate increases too, so we see an ...
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1answer
670 views

Size of electromagnet needed to replicate Earth's magnetic field

I guess the title says it all. How big of an electromagnet would you need to generate a magnetic field the same as Earth's? Like, what kind of amperes are we talking here? (Assuming a hypothetical ...
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2answers
37 views

Kinetic energy and current

When a battery is connected to a resistance circuit, we know that it loses energy because heat is emitted as a result of the collisions between the electrons and stuff, but my question is, is the ...
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1answer
28 views

Why isn't $V_L$ not equal to $i_LR_L$ according to Thevenin's theorem?

According to Thevenin's Theorem $I_L= \frac{V_{th}-V_L}{R_g}$ whereas $I_L$= current through the load. $V_{th}$= The potential difference across the load resistance when the load resistance is ...
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13answers
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What *exactly* is electrical current, voltage, and resistance?

I am taking AP Physics right now (I'm a high school student) and we are learning about circuits, current, resistance, voltage, Ohm's Law, etc. I am looking for exact definitions of what current, ...