Questions tagged [conductors]

For questions about materials which allow the flow of an electric charge (electrical conductors) or the transfer of heat (thermal conductors) through them.

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Charge distribution on a conducting solid disc [closed]

Imagine that you have a disc of radius $R$ with charge $Q$ on it. It is a conducting disc. What would be the charge distribution? Is there a uniform distribution over whole area? $\sigma=\textrm{...
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Why is stainless steel a poor conductor of electricity?

I recently had a metal plate put in my shoulder and was wondering why stainless steel isn't a good conductor (At least I hope it isn't). Does the alloy just lack free electrons? Why is that?
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Why is gold used in computer parts when Silver and copper are not only better conductors, but cheaper? [closed]

I was reading a question and found this interesting answer. https://physics.stackexchange.com/a/334378/113093 Which mentions these materials that aren't very conductive, that are used in every day ...
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397 views

Temperature distribution in a current carrying conductor

A rod of uniform cross section and composition is connected across a battery. Let the middle part of the rod(when divided into three equal parts) is heated uniformly. A book says that the temperature ...
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1answer
702 views

Will heat flow by conduction oscillate until thermodynamic equilibrium is reached in a solid object?

Consider the following thought experiment with $2$ conducting objects $A$ and $B$, where object $A$ is initially at a much higher temperature than object $B$. The objects are now placed in perfect ...
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Force on a point charge $q$ inside a cavity in an uncharged conductor

This is problem 2.40 from Introduction to Electrodynamics by D. J. Griffiths: A point charge $q$ is inside a cavity (not necessarily spherical or anything similarly regular) in an uncharged ...
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Rigorously prove that electric field is zero in a perfect conductor

I have ran into a problem while trying to prove that the electric field is zero in a perfect conductor My argument went something like this: We know that: $$\vec J = \sigma \vec E$$ In a ...
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107 views

How do electrons lose their kinetic energy in ideal wire?

Electrons keep accelerating due to the electric field (produced by the battery) along the circuit. So electrons gain kinetic energy, hence their drift velocity changes. But this is not the case: ...
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345 views

Why do electrons follow the conductors shape?

I'm stuck thinking about this situation. I imagine that there are two oppositely charged objects at short distance $r$, put inside an insulator (Can I say air?). They generate a net elctric field, ...
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4k views

Why is soil more conductive than water?

Compare the following two sources: High quality deionized water has a conductivity of about $5.5~\mathrm{\mu S/m},$ typical drinking water in the range of $5$-$50~\mathrm{ m S/m,}$ while sea ...
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697 views

Electric field below conducting plane

In Griffiths introduction to Electrodynamics, the classic image problem is presented: There is a charge $q$, above a grounded conducting plane. Griffith says that the electric field below the plane is ...
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889 views

Drift velocity in Drude model

this is a very short question, probably I'm missing something really simple: according to Drude model, we have for the drift velocity of electrons, being also the average velocity: $$ v_d = \frac {-e ...
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483 views

How free and bound charges in metals interact?

In dielectrics, distortion polarization of bound charges occurs in response to applied electric field. In metals, free charges produce current in response to applied electric field, but metals have ...
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217 views

Some confusions regarding electrostatic shielding

A spherical conductor A contains two spherical cavities as shown. The total charge on conductor itself is zero. However, there is a point charge q1 at the centre of one cavity and q2 at the centre of ...
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1answer
31 views

Plane of charge versus plane of charge on surface of conductor

The exercise below aiming to test my understanding has me confused: Why is the answer $(B)$? To me, I can envision for infinite planes of charge that its electric field lines are leaving normal to ...
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1answer
379 views

Propagation of EM waves through antenna

I read in the book that when we apply high-frequency signal to a conductor, the signal propagates as a sinusoidal current in a conductor. But when the conductor is connected to the antenna, the signal ...
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1answer
7k views

Surface charge density relation with the radius of curvature at the surface of a conductor [closed]

In a text book it was given that the surface charge density of a conductor at a particular region on its surface is inversely proportional to the radius of curvature at that region. I didn't ...
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1answer
267 views

How do electrons actually move in a wire? [duplicate]

Do they jump from atom to atom or are they free-flowing? Where does resistance fit in? Do electrons physically HIT the atoms? If so, how do they hit atoms if the nucleus is small and far away from the ...
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695 views

Hollow conductor containing charge: why is internal field cancelled outside and why are the field oustide the cavity zero inside the cavity?

I've a doubt on the following situation. Consider a hollow conductor $A$ (of arbitrary shape) containing another conductor $B$ (again of arbitrary shape), with a positive charge $+q$. By the ...
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How does crystal lattice explain electrical conductance?

From http://education.jlab.org In a metal, the atoms are arranged in a crystal-like configuration. ... Now, in a metal, the valence band is relatively close to the conduction band - ...
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1answer
488 views

Why does a conductor shield its inside from its outside, but not vice versa?

A point charge outside a hollow conducting sphere will produce no field in the hollow interior: the metal shields the interior. But a point charge inside the hollow interior will produce a field ...
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1answer
335 views

Local nature of a surface charge density

Boundary $S$ of a cavity in a very large (perfect) conductor is a connected compact (smooth) surface. A positive point charge $+q$ is placed inside this cavity. From Gauss' law we know that the total ...
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82 views

Why is the electric field between two conducting parallel plates not double what it actually is? [duplicate]

According to here: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesht.html We can treat two parallel plates as being a single conductor which has an electric field of $\frac{\sigma}{\...
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995 views

Method of images and induced charge

I've read the section in Introduction to Electrodynamics by Griffiths over and over and I still don't understand the concept of the method of images. This problem builds on the concept of using an ...
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3k views

Why is the magnetic force experienced by a current carrying wire perpendicular to the length of the wire?

I don't quite understand why the force is perpendicular, can somebody explain with a magnetic field diagram as to how the perpendicular direction is produced as a result of the interaction of the two ...
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Skin effect fully explained by plane wave attenuation?

I went over the explanations of the skin effect in multiple sources. However, I still don't understand how the fact that this equation: \begin{equation} (\Delta - \mu_0\sigma\partial_t - \frac{1}{c^2}...
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Charge distribution on plates [closed]

$A,B,C$ are $3$ identical metallic plates. Initially, charges $Q$, $4Q$ and $2Q$ were given to $A$,$B$ and $C$ respectively. Find final charge distributions when $B$ was earthed and $A$ and $C$ were ...
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If we know the units of a quantity is it valid to write a formula just so that the units are dimensionally correct?

Here is a very simple example: The definition of an electric field is $$\vec E = \frac{\text{Force}}{\text{Charge}}=\frac{\vec F}{Q}$$ and it's dimensions are N$\mathrm{C}^{-1}$ (Newtons per Coulomb)...
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Charge inside conductor

I know that the $E$ field inside a conductor is zero. What happens if I put a source of charge inside the conductor? Say the conductor was spherical centered on the origin and there exists a charge ...
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Is current the speed of the electrons?

My teacher got me really confused this time. He said that current is the rate of flow of charge. If this is true, then current could be the speed of the flow of charge (ie. the kinetic energy of the ...
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Electric Field within the cavity of a conducting sphere?

So the hypothetical situation that I am confused about is below: The situation consists of a point charge, +q, contained within the cavity of a spherical conductor of neutral charge. I understand why ...
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2answers
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Why do electric field lines start and end at 90 degree at the surface of a conductor? [duplicate]

There is one property of electric lines of forces which states that: Electric field lines start and end at 90 degree at the surface of the conductor. But why is that so? Is there any proof for ...
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6answers
150 views

Why is it assumed that magnetic forces arising from magnetic fields do not do work on a current carrying conductor?

Imagine a long, thin current carrying conductor carrying a current $I$ and moving through space with a velocity $\mathbf v$. If there exists a magnetic field such that there is a force on the current ...
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569 views

Quantum mechanical interpretation of resistance and voltage drop

It is generally said that Ohm's law isn't a real law since it is only a fine model found through experiments to explain the nature of circuits. And resistance is defined as the ratio of the voltage ...
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545 views

Is Ohm's law valid for all frequencies?

From continuity equation and Ohm's law it it's possible to say that: $$ \nabla \cdot (\sigma \mathbf{E}) = -\frac{\partial \rho}{\partial t} \Rightarrow -\frac{\partial \rho}{\partial t} \frac{1}{\...
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Why are there no charges inside a conducting sphere?

Why is it necessarily true that all charges occupy themselves only on the surface of a conducting sphere, and not anywhere inside the sphere? One argument is that if a charge were to be inside a ...
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Are insulators non-ohmic conductors?

Can insulators/ dielectrics be considered as non-ohmic conductors ? As they apparently breakdown when sufficiently large potential differences are applied across them.
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Conductance and conductivity

What is the relationship between conductance and conductivity? Is there any formular that can explain their relationship? I am so confused.
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Electric field inside a conductor and induced charges

My textbook says two different things and I'm not sure how to reconcile these two: electric field inside a conductor is always 0. for a conductor with a cavity with a charge q inside it, the field ...
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3answers
1k views

electrostatic shielding

When we have an uncharged conductor with a cavity and apply an external electric field, the charges rearrange to keep the electric field inside the metal zero. The driving force is the need to keep ...
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710 views

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 ...
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113 views

Bubble of air in resistor follows $ r^{3}$ law?

I used a program to simulate the resistance of a resistor when a small bubble (compared to size of the resistor) of air of radius $r$ was placed inside the resistor, as $r$ increased. I plotted the ...
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411 views

How does the force on two positive point charges change when an infinite conducting plane is inserted? [duplicate]

This kind of a configuration struck me when I read this question. The original question asked how the force on the two charges would change if a metal plate was inserted between them. This question ...
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Why is the electric field around a hollow spherical conductor homogeneous, even with an off-center charge inside?

I have a lot of records in EM, and I know all about charge induction and Gauss's theorem for systems of conductors, nonetheless I still have a problem that I cannot face without feeling uncomfortable. ...
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1answer
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What is an ohmic conductor?

Is it a conductor whose temperature doesn't change when you increase the current through it, or a conductor whose resistance is constant provided its temperature doesn't change? I've seen it defined ...
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6answers
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Do electrons flow only on the surface of a wire?

Since the $\vec{E}$ field inside a "perfect" conductor is zero, do the electrons(the current) flow only on the outer surface? This has bothered me since I studied electromagnetism. Thank you for ...
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240 views

Charge distribution in the wires and resistor, in a DC circuit

1) How do the electrons in a wire with 0 or negligible resistance arrange themselves in order to make the field in the wire 0? 2) The electric potential drop across a resistor is far more than ...
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181 views

How the current moves in the battery and outside the battery?

Does it move again to the negative terminal or stays at the positive terminal until the electrons all come .so the voltage will.be zero and current flow .I want simple clear explanation because i am ...
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600 views

How is the speed of electricity determined?

Before I am told this is a duplicate, I'd like to be specific here. I have searched online for an answer regarding the speed of electricity in general and haven't found what I'm looking for. Even in ...
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1answer
95 views

Direction of AC current in a very long wire [closed]

Suppose an external wire of length 10^8 meter (very long indeed) is connected in between the slip rings of an AC generator externally. Taking the speed of current propagation to be ~10^7 m/s, then it ...