# 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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### Diffusion current in semiconductor while applying an electric field

In case of intrinsic semiconductor, while applying an electric field, only drift current should exist, right? As diffusion current is due to concentration gradient. So the electron flow will be ...
201 views

### Magnetism And Special Relativity

I've read an explanation about 'how moving charges produce magnetic field' according to special relativity. It proves how magnetic force is just another artifact of electric force viewed from a ...
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### Why can't excess charge travel through an insulator?

Lets say you have a closed circuit connected to a battery made of copper wire. Lets say that at one point of the copper wire there is plastic. The electrons can't flow through the insulator and back ...
40 views

### Do wires with DC current vibrate like wires with AC current (very tiny vibrations)?

Do wires with DC current vibrate like wires with AC current (very tiny vibrations)?
232 views

### Magnetic force acting on a current carrying wire

I am a high school student and I would like to know why in a magnetic field the Force, $F$, is equal to $BIL\sin(\theta)$, where $\theta$ represents the angle between the magnetic field and the ...
111 views

### What does an induced emf do to a loop of varying current?

I know that the magnetic flux through a loop in space is proportional to the current such that $\Phi=LI$. Therefore a change in magnetic flux will produce an emf, so $\mathscr{E}=-L\dfrac{dI}{dt}$. ...
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### How to calculate the summary of input current in finite element model?

I have a finite element model of homogeneous conductor in electricity with stable voltages setting. For simplicity, the conductor is in 2d dimension and a round shape. The boundary is insulated. I set ...
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### What is the difference between current and the ampere?

I have always thought that current has the same definition as the ampere. When this problem comes up: So I instinctively choose answer A. But according to the my book, B is the answer?!?! But why? ...
32k views

### Speed of light vs speed of electricity

If I arranged an experiment where light raced electricity what would be the results? Let's say a red laser is fired at the same time a switch is closed that applies 110 volts to a 12 gauge loop of ...
235 views

### Time-varying magnetic field and classical electrodynamics

My question relates to magnetism and classical electrodynamics. The following is a reference. This question says $\downarrow$ (do not answer to this): $N$ sources of current with different emf's are ...
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### How to measure the distribution of electrical potential in water?

I read somewhere that they used micro-electrodes, where the reference electrode was placed in a glass filled with KCL and the probe electrode in the water that was to be measured an used a motor and ...
758 views

### Does direction of current in Node Voltage method circuit analysis matter?

I am trying to solve the following circuit using the node voltage method, but I'm having issues with figuring out how current is supposed to flow in and out of nodes. I understand that the current ...
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### Continually increasing current for same potential difference when resistance is zero

Given a circular wire connected to a battery with a potential difference of v across the wire. And given the fact that resistance in the wire is zero. If a constant potential difference is applied ...
410 views

### 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 ...
131 views

### What exactly does Ohm's law say?

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, R ...
556 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 ...
160 views

### Brightness of lamp

Brightness of lamp (power) depends on two factors: Current which flows through the lamp. voltage (p.d) across the lamp. In the figure: When the variable resistance increases, what happens to the ...
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### What is the area $A$ in the magnetic flux for AC generator and a coil?

I am getting confused with what area do you use in AC generators and coils. Let me explain: in an AC generator, there are two coils that rotate. When using the equation - magnetic flux $= BA\cos(x)$, ...
236 views

### Electric current dipole moment

Electrical Current Dipole of dipole moment $\mathbf{p_{EC}}$ has unit of $A\cdot m$. My knowledge of dipole moments unfortunately stopped in high school where I learned that dipole moment $\mathbf{p}$ ...
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### What does 'Oppose a Change in Current' really mean from Lenz Law?

We all know what Lenz Law is, but I have a bit of trouble conceptualizing the phrase above. Does 'Oppose a Change in Current' means it will take more time for the current to increase to its maximum ...
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### How can I simplify this circuit? And how can I find the Thevenin equivalent for it? [closed]

I am struggling to find a more simplified version of this circuit, which in turn is making it more difficult for me to find the Thevenin equivalent for it as seen through the RL resistor. The line ...
551 views

### Current in discharging capacitor through fixed resistor?

In the textbook I'm using for physics it says that the charge left on the plates of a capacitor after time $t$, that is discharging through a fixed resistor, is $Q=Q_0e^{-t/\tau}$ where $\tau=RC$ is ...
39 views

### Time Constant of a Capacitor in DC

I've just started studying Physics and I'm not sure how you're supposed to calculate the time constant of a capacitor when a direct current is applied. DC means that frequency equals = so the ...
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### How does having free electrons make something a conductor?

My question is how does having free electrons make something a conductor? I know that the flow or movement of electrons create a current but can't you just add free electrons (such as a battery) to an ...
31 views

### What makes a conductor able to pass electricity?

My question is what makes a conductor able to pass electricity? I know that conductors have free electrons where as insulators don't have as many but can't you just add free electrons to the insulator ...
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### Why, when an electromagnet is connected to a circuit, does the electric current not reach the required strength immediately, but gradually? [closed]

When an electromagnet is connected to a circuit, the electric current does not reach the required strength immediately, but gradually. Why? When the battery terminals of the flashlight are briefly ...
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### What does the labelling of a conductor such as: 24 W 12 V mean? Does this mean the resistance of the wire or the current?

So I came across a question where a lamp was labelled 24 W and 12 V. 2 lamps that were identical and had this labelling were then put in series with a voltage supply of 12 V. Obviously the individual ...
598 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 ...
28 views

### Drift of electrons in a conductor connected across battery terminals and constantly being heated

I came across this question which was suggested to me by a friend . In this question , the correct answer marked is d , which states that the conductor will have highest temperature near D end . I am ...
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### Physical meaning of $F^{0\nu}j_\nu$

In my problem I showed that $F^{\mu\nu}j_\nu$ is a contravariant 4-vector. Now the question is what is its 0-component's physical meaning, i.e. the meaning of $F^{0\nu}j_\nu$ if $F^{\mu\nu}$ is the ...
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### Why doesn't a conducting wire in a constant magnetic field experience a force in the direction of the magnetic field?

Instead of using the wire's magnetic field for deriving using Newton's third law can't we do the opposite using the magnetic field produced by magnet ? I mean why doesn't the wire simply move in the ...
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### Why don't electrons still have energy after completing a circuit with a battery?

Firstly a battery causes an accumulation of electrons in the negative terminal right? Hence the positive terminal is relatively positive and so an electric field is produced. This electric field will ...
360 views

### How to vary the current using batteries?

I am making a door bell as a school assignment. It works by having a solenoid produce a magnetic field which attracts a pice of iron attached on a conductor. when the iron is attracted towards the ...
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### Why does a real DC circuit with 1 resistor have uniform current?

Imagine a DC circuit with small but non-zero resistance in wires and large resistance in a single resistor in series with the battery, all ohmic. Connecting the battery I imagine a surge of electrons ...
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### Ohm's Law gives me different values compared to the practical experiment with a multimeter - can you explain why?

I am studying physics in high school and am trying to understand electronics. Using Ohms law I calculated VIRP values for a simple circuit with three 1000 ohm resistors and a 9V battery. I then set up ...
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### Can non-harmful eddy currents be used to heat water? [closed]

I think after 'googling' some web sources that eddy currents are strictly localized in a volume of iron surraunded by a loaded inductive coil so can not cause an electric shock to a person while the ...
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### Are voltages in series LCR circuit added vectorially?

I am trying to understand Kirchhoff's voltage law in reference to AC circuits and this is a dummy problem I have solved to show my doubt.Quoting my textbook, voltages across components in a LCR ...
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### Bound current and Eddy current

I Know that bound currents are due to magnetization of any material while Eddy current is due to rate of change of flux through a metal so I wanted to know whether both currents are are independent ...
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### Is this explanation of electromagnetic induction correct? More specifically interpreting Lenz Law

When the magnet, starting with the north pole, goes towards a coil of wire (maybe a solenoid???) the magnetic field within the wire changes polarity in order to repel the north pole. This is so that ...
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 ...
14 views

### Bandwidth of a RLC Circuit

Bandwidth of an RLC circuit is defined as the angular frequency difference for which Power dissipated through circuit is half of that dissipated at resonance. What is so special about this range that ...
1k 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 ...
186 views

### Best visualization of electric current and voltage

I asked this exact question on the electrical engineering stack exchange, and it was suggested that I post it here: So, I want to know what the best way to visualize what is actually happening in a ...
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### Does the drift velocity of electrons in a wire having constant length and a constant voltage applied across a depends on the area of cross section?

I used the formula Current=charge densityĆ e Ć area Ć drift velocity i.e. i=neAV So this yield that drift velocity inversely proportional to area of cross section But the answer to this question is ...