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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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20 views

Wheatstone bridge circuit diagram [duplicate]

How can we draw any Wheatstone bridge circuit from a given circuit
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Galactic Birkeland currents

Does Milky Way or any other galaxy produce Birkeland currents such as seen on Earth in auroras? If yes, how strong would they be?
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Nickel plated steel strip for li-ion Battery pack - Purpose of Nickel Plating?

I am trying to build a battery pack from 18650 batteries, each interconnection is made from steel strip, most '18650 strip' has a steel core with nickel plating. I have a question regarding the ...
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1answer
32 views

How is the voltage in this parallel circuit different across each component?

I'm studying up on circuit calculations and came across this circuit: I was taught that voltage in a parallel circuit is the same across all components, which would be the voltage supplied by the ...
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1answer
38 views

Is the current same everywhere in a series circuit?

When we say that the current flowing in a series circuit is the same, do we mean that the current is sane in the entire circuit i.e, charge per unit time is the same in the entire circuit at any point ...
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1answer
72 views

What is the use of resistors connected in series? [on hold]

If the current in a series circuit remains the same, then what is the use of a resistor? I read somewhere that as electrons flow through a circuit, they are accelerated towards the positive terminal, ...
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38 views

Current Density In a 3D Loop - Discretising a Model

I'm working on a finite element model as part of a line of research. Specifically I'm consider using vector finite elements (i.e 3 values x,y,z per node) to solve the Poisson equation in magneto-...
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2answers
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Can we say $i=i_{0}\lvert\sin(\omega t+ \phi) \rvert$ is alternating current?

$$i=i_{0}\lvert\sin(\omega t+ \phi) \rvert$$ $i_{0}>0$. Can we say that the current described by the above equation is an alternating current? $$i=i_{0}\sin(\omega t+ \phi)$$ We are mostly ...
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1answer
55 views

Why aren't salt water batteries used to power cars instead of lithium-ion?

I know salt water batteries are less efficient than lithium-ion, but water is safer, can be found anywhere, is cheap and 100% ecological. Even if it doesn't last long, you can refill anywhere. Why can'...
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2answers
33 views

In current flow, do electrons propagate simultaneously or one after another?

If we have 2 atoms (atom 'A', atom 'B') each with their own electron (A: 'Ea', B: 'Eb'): When Ea jumps from A -> B, simultaneously, is Eb in the process of jumping from B -> 'C'? or does Eb only ...
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2answers
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DC Motor: Split rings vs commutator [closed]

Question: In a simple DC motor (as shown below), explain the effect that replacing the commutator with slip rings would have on the operation of the motor, if no other change was made? My Attempt: I ...
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1answer
58 views

Kirchoff law of circuit confusing me

I have read that kirchoff first and second rule is in accordance to law of conservation of charge and energy respectively.But I cannot relate how it does justify.KCL just states that incoming current ...
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43 views

Vector potential, magnetic field and dipole moment due to a rotating cylinder

I've been struggling with the following problem: Consider a cylinder with height h and radius a with a homogeneous surface charge density $\sigma$ rotating about its symmetry axis with constant ...
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1answer
44 views

Current and Electricity

Is it possible that a current flows across a resistor although there exists no difference? If yes than how? Is this not a contradiction of ohms Law?
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Are the electric flux lines between the fixed nucleus and the moving free electrons in the wire cut when an electric current flows in that wire?

According to the displacement current theory, An electric flux variation around the wire is "I" when an electric current in that wire is "I". Please, check the following paper and equation (18) ...
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1answer
29 views

What's wrong about Maxwell's equations for a Hall probe?

I am using Maxwell's equation to analyse the current and electric field of a Hall Probe. A Hall probe is basically a thin sheet of metal with a current through it. When a uniform magnetic field $\def\...
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1answer
17 views

Current through a loop symmetric about a current carrying wire

For part (b) where the current i is increasing, the answer is apparently that loops 1 and 3 have zero current induced. This doesn't make sense to me. The magnetic flux is changing through the area of ...
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1answer
6 views

Do surface currents in superconductors only arise due to an externally applied magnetic field?

On the topic of surface currents or (screening currents) which are responsible for non decaying eddy currents that expel an externally applied magnetic field, does this phenomenon only occur when ...
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2answers
36 views

Contradiction about the direction of magnetic force

I have encountered two contradictory directions for the force felt by current in a wire immersed in a uniform magnetic field. Halliday says the force should be to the left in the situation pictured ...
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1answer
29 views

Switching the position of voltage probes changes the sign of the measured voltage. How can you determine the charge sign in a Hall effect then?

When you measure the voltage in a battery, for example, you place the voltage probes at the battery ends and get, let's say, a reading of 1.5V. If you change the position of the probes in regards to ...
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62 views

How does a resistor really alter the voltage across it?

This answer sums up the reason why a resistor does not alter the current flowing through it in a circuit. Let's say that we have a $10$ $V$ battery connected with two resistors of resistance $3$ ...
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2answers
53 views

Will the power dissipated in a resistor in an AC circuit vary with frequency?

In a recent examination I had a question where the examiner asked if the brightness of a bulb connected to an AC source would vary with frequency of AC source. The right answer was that it would vary, ...
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1answer
33 views

What causes current to move to the surface in superconductors?

I’m really trying to understand superconductors in an intuitive way here, although many say you cannot, anyway Im unable to find anywhere that explains to me why the current is on or near the surface ...
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3answers
49 views

Conceptual Understanding of Zero Curl in Ampere's Law

I understand that Ampere's law tells us that the current density times $\mu_0$ at some location must be equal to the curl of $\mathbf{B}$ at that location. However, conceptually this is troubling me. ...
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3answers
87 views

Is it true that whatever current enters a battery, also leaves the battery? Why?

How is it true that whatever current enters a battery also leaves the battery? Is it due to one of the Kirchhoff's laws? Can anyone show how that is? How can I reach this conclusion logically/...
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1answer
40 views

Relationship between current and voltage (I know little physics)

I'm a little confused about the relationship between voltage, current and resistance. I do know V=IR; but as to the relationship between voltage and current- (holding resistance to be constant) does a ...
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2answers
41 views

Can non-ohmic conductors have a constant resistance?

The diagram below shows the relation between a direct current I in a certain conductor and the potential difference, V, across it. When V < 1.8V, the current is negligible. Which ...
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1answer
44 views

Maximizing power, current, voltage

We're asked to maximize voltage across the resistor RL, then do the same for current and power. But to find a value of R that maximizes VL, I think we'd just say infinity. And to maximize current ...
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Confusion about non-ohmic conductors

Could someone please explain what happens in a non-ohmic conductor when the voltage is dropped in terms of current and resistance? It would help me a lot if it were done in detail. I don't understand ...
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1answer
49 views

What causes a magnetic field to be produced at a point in space, when an electric current is flowing nearby?

We know that a current induces a magnetic field along a circular path around it But what exactly causes the magnetic field to produced in that point of space? Is it that change in the direction or ...
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2answers
49 views

Confusion about Ohm's law

So does ohms law say if the resistance is increased the voltage will also increase but not the current? And in non ohmic conductors the current increases with the voltage even though the resistance is ...
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1answer
26 views

If the cross-sectional area of a wire doubles shouldn't the current also double?

In this question the answer is B but I don't understand how that could be possible considering the area has doubled.
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1answer
32 views

Using ammeter to measure voltage

Suppose you have the following circuit: Where R1 = 1 kΩ, R2 = 2 kΩ, R3 = 3 kΩ, R4 = 4 kΩ, R5 = 5 kΩ, Vs = 5V. The voltage in the branch with R5 is then 5 I where I over R5 is .064A. Suppose you ...
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35 views

Why can two nodes at the same potential be collapsed into one node?

I have a problem where I have a cube with resistance $R$ along each edge. I am asked to find the potential between various nodes (corners) using symmetry and the fact that two nodes at the same ...
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2answers
36 views

Voltage Change Across a Resistor/Circuit

Say you have a 9 volt battery, and you connect the two ends of the battery with a wire to form a circuit with no resistor. If you measure the potential difference between the two ends of the battery, ...
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A doubt and different approach regarding “A hypothetical magnetic field existing…”

A popular question from the book HC Verma's Concepts of Physics goes like this:- "A hypothetical magnetic field existing in a region is given by $$ \vec{B}=B_{0} \vec{e}_{r} $$ where er denotes the ...
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2answers
42 views

Proof of continuity of voltage across a capacitor

It is known that the voltage drop across a capacitor is a continuous function of time. This means that, for each instant t0, we may write: V(t0-) = V(t0+) This relationship is very used in the time ...
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2answers
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Confusion in usage of formulae for power dissipated in a circuit

When should we use $\frac {V^2}{R}$ and when to use $I^2R$. Because many times they ask about the power without giving details about series and parallel. I am really confused
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2answers
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What am I supposed to look for in the question “What is the total resistance between $X$ and $Y$?” [closed]

I'm not really concerned with answering the question but more so what I'm trying to look for. The question is "Three resistors are connected as shown. What is the total resistance between $X$ and $...
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Relation between AC Current and electromagnetic wave in transmission lines?

I m so confused we started by learning about electromagnetic waves in the vacuum , then we went to transmission lines and there the professor mentioned the em waves are traveling through them. I ...
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1answer
38 views

Can any other thing rather than current pass through conductor? [closed]

A conductor is an object or type of material that allows the flow of charge (electrical current) in one or more directions. Materials made of metal are common electrical conductors. Electrical current ...
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1answer
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Meaning of negative emf in the context of Kirchhoff’s Voltage Law

I’m wondering what it means when the emf of a battery is calculated to be a negative value through Kirchhoff’s Voltage Law. This is the problem: As you can see, we’re given the currents, and we can ...
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2answers
58 views

Could you transmit electricity wirelessly?

Since you can wiggle an electron to get a radio wave And if you 'wiggle' it fast enough you get higher and higher frequency right? So couldn't you just broadcast an electromagnetic beam or whatever ...
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1answer
74 views

Some confusion regarding RLC circuits

I'm a mathematics student, and it has been years since I last did current/voltage/resistor related subjects in high school. However, for one problem that I've encountered, I actually need to calculate ...
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1answer
31 views

In a simple resistor circuit, does the current reach V/R instantaneously?

Essentially, if I were to plot current against time for a simple circuit with a DC cell and a resistor in it, would there be a non-flat profile from time $t = 0$. So, between $t = 0$ and $t = t_1$, ...
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3answers
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Stumped on understanding a Feynman lecture about force from wire on magnet

I must (sheepishly) admit that I'm stumped on a beginning page of The Feynman Lectures Volume 2. I have included a picture from the page. [Let me know if I'm breaking copyright, or if I can include ...
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What does it mean by an AC of Infinite frequency?

For an AC of infinite frequency, Time period= 1/frequency = 1/$\infty\ $ = 0 So, this means the polarity of AC is 'reversed in every 0 seconds'? Can you clarify this phrase?
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Relation derivation based on the definition of Current Density

The current density is defined as: $$\textbf{J} (\textbf{r},t) = \rho(\textbf{r},t) \cdot \textbf{v}(\textbf{r},t)$$ where $\rho (\textbf{r},t)$ and $\textbf{v}(\textbf{r},t)$ is the charge density ...
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6answers
76 views

Potential difference and current

According to Ohm's law: $V=IR$. Therefore $V$ is directly proportional to $I$. Furthermore, $V=W/q$ and $q=IT$. Thus $V=W/IT$. Therefore $V$ is inversely proportional to $I$. How can $V$ be both ...
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1answer
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Charge stored in a capacitor with dielectric when relative permittivity varies

Suppose the relative permittivity of the dielectric in an uncharged capacitor of capacitance C varies with the voltage applied, e.g. k=xV where x has dimensions of V^-1 (After this capacitor is given ...