# Tagged Questions

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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### Lightning, Electrical breakdown, and Current

Recently a discussion came up about this gif: http://i.imgur.com/r9Q8M4G.gifv This lead to a few questions about electrical breakdown of insulators. The disagreement we're having is whether or not a ...
928 views

### Why is current the same in a series circuit?

So I am a 10th grade student and my teacher told me that the current is the same at every point in a series circuit. It does split up in parallel circuit but it then recombines and the current flowing ...
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### Why is the electric field perpendicular to a circuit zero?

Griffith briefly addresses the uniformity of the electric field in a wire using Laplace's equation by assuming that the electric field is always parallel to the wire (i.e. $\mathbf{E}\cdot\hat{n}=0$). ...
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### Question regarding Kirchoff's loop rule

My problem is that there are n cells connected in parallel which are connected to an external resistor. Now can we use Kirchoff's loop rule to evaluate the current through the resistor by considering ...
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### What happens to metal when exposed to an electric current for an extended period of time?

I was wondering what happens to the actual metal (copper, aluminum, silver, gold) when electricity is ran through it for a long period of time. Say years like the wire in a house. Does the ...
3k views

### Why don't loop currents produce light?

If a charge travels in a circle it must accelerate, thereby producing EM. However, a wire in a circular loop is analogous to many charges moving in a circle. So, why don't circular currents produce ...
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### Current carrying conductor

In a current carrying conductor, the net flow of charge is zero. Is this possible? Arent the charges moving? Are the charges moving in a current carrying conductor?
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### Range of voltmeter [closed]

I have understood how the range of an ammeter cannot be decreased. But I don't seem to understand how the range of a voltmeter can be decreased. Pls help.
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### Why ohm started his derivation from $V$ is directly propotional to $I$ but In his statment he says $I$ is directly propotional to $V$? [closed]

Why ohm started his derivation from $V$ is directly propotional to $I$ but in his statement he says I is directly proportional to V?
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### Same current flowing [closed]

In the following circuit how can we say that the current flowing through both the $4\Omega$ would be same . I know it would be same if in middle the $\frac{2}{3}\Omega$ is not there but here it is ...
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### Does removing half of toroidal ferromagnetic core significantly reduce flux density in the remaining half?

Assuming a DC current in a cable has induced a magnetic field around the cable, and a ferromagnetic toroid is used to concentrate the field; if half of the toroid were cut away (so the cable is no ...
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### Circuit with voltage source, resistance and current source

Suppose I have a (closed) circuit with a voltage source $V$, a resistance $R$ and a current source $I$ (in this order). Is it true that the voltage across the current source is $V-RI$ ?
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### On touching the negative terminal of battery, shouldn't this negative charge flow to earth?

On batteries one terminal is clearly mentioned as negative. I wonder can we neutralize this terminal by just touching it with finger? In electrostatics it is common to neutralize a charged object by ...
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### Current through a chargedwire

When current is passed through a conductor which is negatively charged ( has excess electrons), what will be the effect on the current due to this charge? In the case of a hot filament used for ...
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### Is the South Pole of an electromagnet always at the end where current is drawn into it?

I'm trying to determine in which direction a magnetic field will be produced in regards to the direction of current in an electromagnet. Will the end of the electromagnet from which current is drawn ...
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### Find the resistance in a mixed circuit

I have this circuit and from what I understand to find the resistance of $R_1$ I need to use $V = RI$. So I found the Voltage for $R_2$ to be $1.5$ V and the voltage for $R_3$ to be $0.996$ V. What ...
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### Won't the Power be dissipated in the first quadrant of this graph?

In the following picture: In the first quadrant of the V-I graph(for an Independent Current Source, where the voltage supplied is positive on the top) won't the power be dissipated instead of being ...
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### What is the voltage drop across a wire [closed]

If we attach a resistor in series, most diagrams only consider the voltage drop across the resistors. What happens when we remove all of the resistors? Why does the voltage drop across the wire become ...
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### Discharging a capacitor

Suppose I have a charged capacitor, meaning there's a voltage (electric potential difference), say, $2V$, between its two plates. We don't know the electirc potential of the individual plates, right? ...
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### What started the magnetic field of Earth [duplicate]

The Dynamo theory gives a good explanation of the magnetic field of the Earth: the Coriolis force focus inner currents into current spirals generating magnetic(s) field(s). What I'm trying to ...
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### Resistance increase with length because of more scattering?

I am referring to one of the answers to this old question. I can't add comment to it because I don't have enough reputation. So here I rephrase the question: does resistance increase with length ...
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### Why alloy have more resistance?

Is there any simple way to understand why alloy have more resistance than metals? My teacher ask this, I answer that, there might be more free electrons in metals than an alloy, but she said you are ...
5k views

### How can a battery charge up another battery to a higher percentage?

Say I have my phone on 5% and a large battery pack on 35% and I charge the phone. By the end the phone is on 100% and the pack is on 12%. How can the battery pack charge the phone up to a higher ...
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### Is the energy needed for a current through a straight and a coiled wire different?

When you add current to a straight piece of wire does it use less electricity than if it was coiled? Does the curve of the wire and proximity to itself make a difference in energy consumption?
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### Can we derive Biot Savart law from Coulomb's law?

Can we derive Biot Savart law from Coulomb's law by setting a current source at an instant in place of one of the charges? Let's say $dl$ is the length of the conductor having $dQ$ charge which ...
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### Even when the drift velocity of the electrons is very small, how is current in the circuit established immediately?

So I have this question in my textbook and Ive also got it in my test. Ive written a wrong answer. My friend wrote the drift velocities of each particle add up and he got full marks. Is it right? Can ...
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### How can a sinusoid be a steady current? [duplicate]

As far as I understand it, a steady/stationary/constant current is defined to have $dJ/dt=0$ (i.e., no explicit time dependence). So I would say that sinusoids cannot produce steady currents, yet ...
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### Earthing, neutral and Earth's conductivity

Ok so this is gonna be a lot of mini-questions. What exactly is the neutral wire? How does earth conduct electricity for a live AC mains even though its just dirt and stones (it should be an ...
20 views

### Change in the EMF of the battery while charging

While charging a battery current is passed from A to B. We form the equation as follows- $$V_A - E - i_r= V_B$$ If the battery is discharged, how can we consider the EMF of the battery in this ...
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### How to properly apply Ampere's Law in this case?(Square Loop)

Suppose ABCD is square loop (conducting). There is a wire carrying a current $I$ into the plane of paper within the region of loop. So how to properly apply Ampere's Law in this case? The closed ...
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### Elementary derivation of $P = UI$ starting from the definition of voltage as work done per unit charge

Consider the following elementary derivation of the formula $P = VI$ for Joule heating of a resistor $R$ for the dissipated power $P$ where the voltage over the resistor is $V$ and the current $I$. ...
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I'm learning electromagnetism from Purcell's book. He say that if we have the following circuit: $$-\frac QC + RI = \mathcal E_0\cos\omega t~,\quad I = -\frac{\mathrm dQ}{\mathrm dt}$$ The ...
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### How does the ion mobility influence the elctrical fiels?

So I have a system of three electrodes, anode, cathode and reference electrode. When I apply a negative current and then register somehow the activity of the sodium chloride solution. Then I apply a ...
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### How do charges accumulate even though current flows through a capacitor?

I don't understand why do charge accumulate on each plate of capacitor.I learned about displacement current which flows through the gap of the capacitor and this makes the circuit continuous.But why ...
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### Applying a voltage to a homogeneous semiconductor

Imagine that there is a homogeneous semiconductor (either a p-type or an n-type, but just one of them) uniformly doped. There is no diffusion current because of the uniform dopage, and there is no ...
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### How to calculate tunneling current between two metals separated by a dielectric?

If I have two metallic electrodes (e.g. Al, Cr) separated by a dielectric (ε, d; e.g. SiO2), how can I calculate the tunneling current as a function of applied voltage?
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### Heat Production in a Current Carrying Wire

The rate of heat production in a wire carrying an electric current is proportional to... The answer is meant to be current with a power (e.g. the square root of current, just current, current ...
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### DC current in a wire

I'm sure that this question was addressed here before, but I failed to find any other instances, so with your permission I ask the question myself. I'm experiencing a very disturbing glitch, there is ...
135 views

### Is resistance proportional to resistivity: $R=\textrm{const}\cdot\rho\;?$

Suppose we have a resistor in a strange shape, filled with a medium of resistivity $\rho$, assuming only Maxwell's equations apply, is it true that resistance $R$ is proportional to $\rho$, even for ...
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### Why does current follow a conductor above a ground plane

Suppose there is a conductor above a ground plane. Current flows from a source through the conductor to a load on the other side. Depending on the frequency of the current the return path through the ...
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### electric current

How can positive charges flow in current? I mean , we know that there is a particle called electron which can move but there is no such positively charged particle which can flow , there can be ...
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### Voltage in parallel and series connection

In series connection, voltage is said to be different and current constant across the circuit. How does it come about ? Is it due to the accumulation of electrons on one side due to resistors? Or, if ...
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### Why do proportionality constants come on only one side?

We know that voltage is directly proportional to current. Then if we change proportionality to equality, we get $V=IR$. Why not $I=RV$??
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### Armature of electric bell [closed]

I want to know that why is the armature of the electric bell made up of soft iron ? I googled this out and everywhere it was written that it is because of its propert to aquire electromagnetism but I ...
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### How SPAD work over Break Down voltage?

SPAD (Single Photon Avalanche Detector) works beyond Breakdown Voltage which is mentioned as Geiger Mode. But how this actually working. When bias voltage aceede breakdown voltage, generally high ...
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### Electrons, Electric Current [closed]

In a DC circuit through a wire, is saying: " Electrons are a flow of matter and electric charge. Protons are a flow of electric current and matter. " the same as saying Electric Current/...
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### Difference in directions of charge and current.?

I just dont understand that why does charge flow in a different direction as that if current when current is the rate of flow of charge.
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### Why is it that for a source of emf, current flows from lower to higher potential?

I'm quite confused about this actually! In fact, I had always thought current flows from a region of higher potential to a lower one. Does it have anything to do with the fact that it's a source of ...