# Tagged Questions

The study of the presence and flow of electric charge. Charges, currents, fields, potentials.

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### Assumption of element for integration

In a round wire of cross sectional radius $R$, current density varies with the radial distance from axis of wire as $J=Cx^2 \, \mathrm{A/m^2}$. Find total current flowing in wire. ($J$ = Current ...
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### Use of rheostat in a potentiometer practical?

in potentiometer practical why a rheostat is used in series to potentiometer wire? as we move the jokey the primary circuit current will also change. so is it to flow same amount of current by change ...
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### Can we use magnetic energy to produce electricity?

Magnets attract each other with a force (magnetic force), because they possess magnetic energy. My question is, is there any way, by which we can convert that magnetic energy into electrical energy? ...
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### Light bulbs Flashing on when disconnected

For the 2nd time I've had a lightbulb flash on in my hand after removing from the power socket. The first time the overhead light in my hallway was out for a couple of days before I got around to ...
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### Could we use nuclear bombs to generate electricity? [closed]

it seems the biggest problem with fusion power is confinement. on the other hand, we developed a fusion bomb in just a few years. i was wondering if it could be economically viable to use nuclear ...
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### If the electric field inside a conductor is zero then how does current flow through it? [duplicate]

I read in a book that when a conductor is placed in an electric field then the free electrons in the conductor will align in such a manner that an electric field is induced which is opposite to the ...
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### Why are electrons negetively charged? [duplicate]

Why have we assigned a negative charge to electrons (and positive for protons)? I feel it would be easier if electrons were positive (thereby, protons negative)- electrons would flow in the direction ...
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### Electrons moving in a simple circuit with a battery and a light bulb

I believe my understanding of electric currents is flawed and want some help to clear up a few things. I'm not looking for a precise scientific understanding, but to understand the basics. I'll try to ...
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### With the help of a given charge is it possible to obtain a charge many times greater in magnitude

Consider a spherically conducting sphere. If a charge(say positive) is placed near the sphere, then it will lead to separation of charges inside the sphere.My question is, can we create charges more ...
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### $P = \frac {v^2}{R}$ derivation confusion [duplicate]

I have always had a confusion of why we use $P = V I$ or $P = I^2 R$ and not $P = \frac {V^2}{R}$ for relating to power loss due to heat in high tension lines. I know there are a lot of ...
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### How does the viscosity of a non Newtonian fluid (ooblek) affect its resistance to electricity?

I know the conductivity of water is based on whatever is dissolved into the solution, hence pure water does not conduct electricity. However, these ions in solution must also be free to move around. ...
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### Which makes for a better equivalent capacitor? In series or in parrallel? [closed]

I understand how capacitors in series and in parallel work. However, I am wondering if it makes a difference, in terms of making a better capacitor that can store more charge, would you connect them ...
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### How does increasing the distance between 2 copper plates in a circuit affect the capacitance? [duplicate]

We have been told that the voltage decreases, but not been given a proper explanation by my teacher. Can anyone shed some light on this? Also, does increasing the distance between the plates of a ...
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### Flux - Scalar Multiplication in Integral?

No textbook and website seems to answer this so here is my question: When we have a scalar flux: I understand that you take the scalar product of the vectors. And I understand the need for using an ...
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### A wall-outlet's hot-slot pulses energy in only ONE direction…toward the ground. How can this be considered ALTERNATING?

I'm trying to "see" electrical-energy transfer, at every viewing elevation (from the femto-scopic level to the macro-scopic level), all the way from the power plant (through the application) to the ...
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### Power lines and cars

A live, active power line fell on the hood of my car. I was told to turn on my car and back away. Was this the proper advice?
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### Loss when transfering electrial energy

Let's say we want to transfer a given amount of electrical energy $E$. We could do this with a voltage of $100\,\rm{V}$, but it's better to transform the voltage to $1000\,\rm{V}$, hence the loss of ...
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### Why does the current in a purely capacitive AC circuit lead the voltage by 90 deg?

1.When we mathematically derive the expression for the current from a sinusoidal voltage source (v=V sin(wt)), we take the derivative of q=cv where c is the capacitance. The final expression we get is ...
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### Generating electricity in space with magnets

Assuming we have a very strong magnet of strength B and of uniform mass in space inside a coil of copper wire of turns N. Also, assuming that the magnet spins at the centre of the coil with no ...
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### Does AC-current reverse direction only in the main circuit (the powerplant-to-powerplant circuit)?

I'm trying to "see" electrical-energy transfer, at every viewing elevation (from the femto-scopic level to the macro-scopic level), all the way from the power-plant to the application. The question ...
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### Why does a rotating aluminium disc slow down when a current carrying coil with iron core is held above it?

What I don't understand is it the Emf induced that slows down the disc or is it a force.
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### High Voltage Powerlines - clarification of energy loss

I've been having a bit of trouble understanding the High-Voltage powerlines. If I was sending power from $A \rightarrow B$, we have: Ohm's law $V = IR$ Power lost in the form of heat $P = I^2 R$ ...
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### Does electricity have an associated entropy?

One can certainly measure entropy changes associated with the generation of electricity, but does electricity itself have an associated entropy (maybe related to voltage, current etc.)?
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### Why does the Emf generated by a magnet going through rings of coil generate a sinusoidal curve of Emf vs time?

I am having trouble writing the reason for the part of the curve to cut the x axis at Emf = 0 and when reason for curve to form max and min peaks.
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### Conceptual Doubt Regarding Electric Circuits [closed]

There are a few questions which have always bugged me. Unfortunately, due to time constraints, I end up memorizing an example, hoping to imitate that knowledge in an exam question. Consider the ...
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### Is it possible to express Fleming's Left Hand Rule and Right Hand Rule in terms of vectors?

I recently studied Fleming's Right Hand Rule and Fleming's Right Hand Rule for electromagnetism (For locating direction of Force, Magnetic Field and Current). Using my hands to find the direction is ...
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### charge on the capacitors

When we connecting a capacitor to a battery of $V$ volts. After it is completely charged, it is disconnected from the battery, and if we connected to another capacitor. In this case, there is no ...
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### Why is Electric field flux through a closed surface in Gauss's law not zero?

I learned that the vector flux through any closed surface is always 0. So if you have a sphere(closed surface) and you put it in an uniform electric field, then the total flux is 0. However, the ...
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### if the voltage is the driving force of the current, how can it lead or lag?

Correct me if I'm wrong on this, but up till now I've assumed that the voltage across a resistor could be seen as both the energy lost by a current passing through it and the energy needed for a ...
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### Batteries Do Not Supply Electrons?

I've read that a battery does not supply electrons, it establishes the electric field that exerts force on the electrons in the wires. This makes total sense to me for AC, but not for DC. The way I ...
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### why is the vertical component of the phasor an imaginary number?

I was learning about the phasor representation of AC circuits, and on adding two out of phase phasors they were each resolved in to a horizontal and vertical component to facilitate the addition. What ...
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### Basic concepts of electrostatics

How to deal with a grounded conducting sphere (I.e finding charge on it) in uniform electric field ? And if any two charged conducting spheres are in each other's electric field then will ones field ...
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### Are AC waves actually a sin function or just appear in their alternating nature as sinusoidal waves?

I mean do we use the graph of a sin wave just as a representation of how the current varies, or are the actual instantaneous values of current really an output of a sin function of the angle the ...
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### Why do they rub rubber with wool while glass with silk and not otherwise?

why not the other way round, and why do they choose wool and silk in particular to charge the rubber and glass rods ?
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### Movement of charges in presence of electric potential difference

This might appear to be a bad question to some but i can't figure out the answer. While reading about an electric circuit, i found this on the web: Over the course of time, one could think of ...
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### Electronic Transport not covered by Bandstructure in Solid State Physics

From what I have read, most of the electronic transport phenomena in solids state physics seems to able to be determined with the bandstructure. Schottky Barriers, bandgaps, band discontinuities can ...
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### Effect of potential difference on capacitance

I've read multiple threads here discussing the relation between capacitance and potential difference and they have begun to confuse me. I have a homework question about which of the following will ...
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### Why are electric shocks felt asymmetrically?

I have been zapping people quite a lot recently (e.g. when shaking hands), probably due to new shoes. What I noticed is that usually I can't actually feel the shock, even though the other person quite ...
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### Why is the electric current instantaneous while the drift velocity of electrons is slow? [duplicate]

The speed of an electron is very slow while going through a conductor(like 1mm per second),but the current passes instantaneous.why?
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### Null point (vector) between n point charges

I have derived the result for 2 positive charges, and for one positive one negative can be obtained by using the minus sign correctly. But I was unable to extend it or solve for n charges. Is my ...
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### What is the reason for extremely high speed of electric current?

I know that electric current is the flow of electrons but electrons have a very slow drift speed (about 2mm/s). How is it that electric current reaches its destination at almost the speed of light?
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### Are objects generally neutral or charged?

Basically the questions relates to what is taught about electroneutrality and has 2 parts: Is the overall charge in the universe zero? Are objects the world generally neutral or slightly charged, ...
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### Amplitude of voltage from centre tap rectifier?

Should be the amplitude of voltage obtained from a centre tap transformer be about half if not rectified? Because in centre tap the potential difference for each half cycle is taken a cross only half ...
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### Wind turbine design question [closed]

I am planning to design a wind turbine that is has rotor blade radius of 0.915m and is connected to a generator. The generators specifications are, it is an ac generator with 5000 coil turnings and a ...
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### Is the electric field strength along an equipotential surface constant?

I'm trying to determine whether or not the electric field strength $|\vec{\mathcal{E}}|$ is constant everywhere on an equipotential surface. I know an equipotential surface is defined as  S = \{\...
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### Magnetic field of rotating charged insulating loop

A charged insulated square loop of side length $a$ is rotated about an axis perpendicular to its plane. What is the ratio of the magnetic field in its centre to the magnetic field of a rotating ...
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### Can current be induced in a grounded conductor?

I'm engaged in a rather lively debate with a group whose physics I believe to be a bit shaky. Basically they're claiming that if a conductive object is grounded to earth, the current cannot be ...
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### Voltage without charge

Can a non-moving charge still have a (nonzero) voltage level? Basically, if i(amperes, measuring current)=0, does V(voltage) have to be 0 too?