# 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 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 ...
1answer
439 views

### Energy dissipation in current flow

In section 4.8, Energy dissipation in current flow, of Purcell and Morin's Electricity in Magnetism, the expression for the power expended by a resistor is derived. The sections includes the following ...
1answer
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### 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. ...
5answers
760 views

### 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 ...
1answer
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### How to calculate flux density in a toroidal CT that has an electrical line pass through the center?

I have seen the Biot–Savart equation, but I don't know how to apply it. Does the conductor length need to be considered finite and equal to the core length, or will the calculation be for a conductor ...
5answers
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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 ...
1answer
218 views

### How can I redraw this circuit where I can apply Kirchoff's Voltage and Current Law to get correct Voltage at V?

I thought I can draw the -5V as a source but it did not turn out to be right, unfortunately.
0answers
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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 ...
1answer
331 views

### Why can't I measure my solar panels short circuit current?

I connected the multimeters COM port to the negative lead on my solar panel, the 200mA port to the positive lead on the panel. I then pointed a lamp at the solar panel the voltage was around 7V, but ...
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 ...
3answers
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### 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 ...
2answers
1k views

### Effect of Current on spring

When Current passes thru a spring , some books mention that it gets compressed. However, I think due to the heating effect of current, molecules will increase kinetic energy and the spring should get ...
0answers
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### 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 ...
4answers
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### Derivation of Ohm's Law

Is it possible to derive Ohm's law (perhaps in some appropriate limit) from Maxwell's Equations?
0answers
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### 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.
1answer
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### 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 ...
1answer
58 views

### 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 ...
3answers
46 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}}{...
3answers
181 views

### 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 ...
2answers
892 views

### Definition of Ampere

On Wikipedia it says: This force is used in the formal definition of the ampere, which states that it is "the constant current that will produce an attractive force of $2 × 10^{-7}$ newton per ...
1answer
29 views

### 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 ...
3answers
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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 $I^2$
2answers
956 views

### What is the value of EMF during a short circuit?

During a short-circuit, 'theoretically' current becomes infinite. But what about the emf? My attempt: Since the potential difference is zero, I guess the emf should also be zero. But again since p.d. ...
2answers
958 views

### What is the aperture in the hydraulic analogy of Ohm's law

Note: My question is duplicate of Why doesn't water come out of tap/faucet at high pressure when I turn it on?. None of the answers given there explains how the continuity equation fits properly. That'...
4answers
2k views

### Why do Capacitors discharge?

I understand how capacitors charge and i know they discharge but i am so confused why they discharge. How do they suddenly know when they are full to discharge. I am doing a school report and really ...
1answer
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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 ...
2answers
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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 ...
1answer
340 views

### Ampere's Law question

If we have a current carrying wire through a rectangular loop, the magnetic field through the loop, according to amperes law, is $\int B\,dl=\mu I$. But what if we have a second wire going through ...
1answer
2k views

### Electric current in quantum mechanics?

Quick question: I want to find an expression for the (electric) current density of an electron, in quantum mechanics. Either a single electron or a general charge distribution $\rho$. Classically ...
0answers
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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?
0answers
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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 ...
2answers
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### 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 ...
3answers
120 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 ...
1answer
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### 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 ...
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 ...
1answer
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### Will electricity follow a path of least resistance on a rotating conductor?

I would like to know if electricity will follow a path of least resistance on a rotating conductor. Please reference the drawing below. This is showing a rotating non-conductive disc with a strip of ...
2answers
47 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 ...
1answer
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### 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 ...
2answers
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### Why is there a phase difference in RC circuit?

In a capacitor circuit,the there is 90 degree phase shift between current and voltage in capacitor(when supplied sinusoidalvoltage and it varies from 0 to 90 degrees in a RC circuit.Can somebody tell ...
1answer
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### Direction of magnetic field around a straight current carrying wire

I am currently studying for O Level and I have been learning about electromagnetism for the past year. The topic has never clicked for me because I've never been taught the true relationship between ...
6answers
219k views

### Why is AC more “dangerous” than DC?

After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...
1answer
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### Why do we use a specific point to find the resistance of a non-ohmic conductor? Why not tangent?

I was wondering why can't the tangent be used to do this calculation? Can a randomly chosen point be used?
0answers
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### Proper utilization of Ampere’s Law

I am tasked with finding the magnetic field due to a bus bar, which seems to have the exact same set up as Problem 7.62 in the fourth edition of Griffiths' textbook on Electrodynamics. To which I ...
2answers
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### Is the electric field in the wires of the parallel circuit always the same and how that affects current?

When we connect two resistors connected in parallel with a battery, it creates an electric field through this wire. well, my question here: Is the electric field in the main wire is the same as the ...
1answer
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### Relationship between concentration and resistance of aqueous solutions

I'm a senior physics/chemistry student working on a practical assignment where I am trying to identify the resistance of CuSO4 in solution (distilled water). I have recorded my data and determined it ...
1answer
756 views

### Diffusion and Drift currents in forward bias

Why do the current in diode in forward bias configuration called "Diffusion current" even if this current is a resultant of external voltage supply which create electric field in diode ,hence should ...
2answers
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### What happens when very high resistance is connected parallelly with low resistance

$1.$What happens when a resistor of very high resistance (say $10,000 \Omega$) is connected in parallel with a resistor of comparatively lower resistance of about (say $100 \Omega$)? Is the ...
6answers
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### Why is high voltage dangerous?

High $V$ low $A$ electricity is transformed into low $V$ high $A$ through a step down transformer for safer use in homes. But how is it any safer? The wattage is the same for the pre-transformer ...
0answers
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### Does the electric current inside a wire fluctuate when the wire shape is changed while still having it connected to the terminals?

The electric current inside a wire depends on the electric field across the infinitesimal segments that the wire consists of. If we readjust the shape of the wire, i.e. make changes to the conducting ...
0answers
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### What causes the magnetic field around a wire? [duplicate]

According to maxwell’s equations, a magnetic field is caused by a changing electric field, but where is this changing electric field in the context of a current carrying conductor that has an induced ...