# 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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### Why can I touch aluminum foil in the oven and not get burned?

I cook frequently with aluminum foil as a cover in the oven. When it's time to remove the foil and cook uncovered, I find I can handle it with my bare hands, and it's barely warm. What are the ...
27k views

### If water is not a good conductor, why are we advised to avoid water near electricity (no wet hands near circuits etc.)?

How can water be a medium to conduct current while its ionisation is so negligible that, in principle, no current should flow?
52k views

### Does electricity flow on the surface of a wire or in the interior?

I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that ...
31k 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 ...
12k views

### How does electricity propagate in a conductor?

On a systems level, I understand that as electrons are pushed into a wire, there is a net field and a net electron velocity. And I've read that the net electron drift is slow. But electricity ...
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### Speed of electrons in a current-carrying metallic wire: does it even make sense?

Does it make sense to speak about the speed of electrons in a current-carrying wire (non perfect conductor)? If so, what is their speed? Here are my thoughts: On the Internet (Wikipedia, ...
5k views

### Why don't free electrons escape from a conductor?

The thermal velocity of the free electron in a metallic conductor varies from $10^5\ \mathrm{m/s}$ to $10^6\ \mathrm{m/s}$. In spite of high velocity, free electrons fail to escape from the metallic ...
10k views

### How does a wire carry alternating current?

Consider a simple network of a bulb whose two terminals are connected to two wires with open ends A and B respectively A o--------💡--------o B Now if a DC ...
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### What keeps electrons on a negatively-charged conductor from leaving?

Imagine a negatively charged conductor in a vacuum. The excess electrons will be spread out over the surface such that the net electric field inside the conductor is zero. What keeps these extra ...
6k views

### Tree vs lightning rod: why does one burn and the other not?

I have this simple question, but I cannot find the answer. I saw this video about a plane getting hit by lightning. In it, Captain Joe explains why people do not get electrocuted. This has a simple ...
5k views

### What is it about the “conduction band” of a material that is distinct from the valence band?

I'm taking a course in nanotech and we're discussing nanoelectronics. This has led to a discussion of conductors, semiconductors, and insulators. I have a number of lovely diagrams explaining the fact ...
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### Are insulators and conductors arbitrary categories?

I have seen charts showing the transition from insulator to semi-conductor is at $10^{-8}~\frac{\text{S}}{\text{cm}}$ and between semi-conductor and conductor is $10^{3}~\frac{\text{S}}{\text{cm}}$. ...
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### Can a conductor run out of electrons to cancel external electric fields?

We have studied so far that electric field inside a conductor if no charge is placed inside is zero. But we know that every conductor has only a limited number of electrons. What happens when ALL the ...
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### Why is there an electric field in a wire even though it is a conductor?

If you take a perfect conductor, there cannot be a field across it since if there were, the particles would arrange themselves in a way to cancel out the field right? Yet, why does the same not hold ...
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### If we remove all electrons from a conductor, how can the positive charge rearrange itself?

Explanations of conductors in electrostatics that I have encountered seem to describe positive charge spreading out, because you could say that lack of electrons can be thought of as abundance of ...
53k views

### Why is the electric field perpendicular to every point on the surface of a conductor?

I am reading Berkeley Physics Course, Volume 2 (Electricity and Magnetism by Edward M. Purcell). I am in chapter $3$, page $92$, and the book discusses conductors. The following is from the book: ...
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### Where do all these electrons come from? [duplicate]

I'm a high school student and I'm fairly familiar with basic electronics, but I've always wondered one thing. So how generators make electricity from motion is the move a magnet around or through a ...
300 views

### Why there is no hole in Sommerfeld's model of free electrons?

My question is very naive. I don't understand why there are no holes in Sommerfeld's model of free electrons? Whenever an electron is excited above the Fermi level $E_F=\mu(0)$, there should be a hole....
2k views

### Do electrons move around a circuit?

We could imagine a simple electronic circuit composed by a power source and a resistor. It is usual find descriptions as "The moving charged particles in an electric current are called charge ...
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### Why do group II elements conduct?

Looking at the periodic table, group II elements like magnesium are known to be metallic, and yet they have full outer shells. So this means they should have full (valence) bands. Now, last time I ...
72k views

### Why is the charge transferred by electrons and not by protons?

Charges are transferred by electrons which we all know. But why can't it be transferred by protons? Well, I searched on Google where I found similar questions already being asked on many sites. ...
10k views

### Why does a short circuit generate fire?

When a short circuit occurs it's obvious that there is fire. How come electric energy turns out to be heat energy? What causes the conductors to get hot when short circuit is present.
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### How does positive charge spread out in conductors?

I know that when there are excess positive charges in a conductor, for example, a metal sphere, the positive charges will spread out over its surface. However, I am confused about how this excess ...
5k views

### Why don't get I shocked in an electric shower if the resistance makes contact with water?

I've found this image that perfectly illustrates my shower. I've read somewhere that the resistance is insulated so even if it touches the water, it doesn't conduct. However, as you can see, the ...
5k views

### Why does electrical current start to flow?

What happens microscopically when an electrical current starts to flow? I'd like to understand microscopically what happens in detail when electrons start moving (quasi-classically). Electrons can ...
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### Why do liquid metals conduct electric current?

This is a question I wanted to ask for some time now. You learn in solid state theory that the free electron model is the reason for metals conducting electric current. The electron orbitals ...
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### Why does electricity need wires to flow?

If you drop a really heavy ball the ball's gravitational potential energy will turn into kinetic energy. If you place the same ball in the pool, the ball will still fall. A lot of kinetic energy will ...
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### How to show mathematically that the electric field inside a conductor is zero?

The electric field is characterized by the equations $$\nabla\cdot \mathbf{E} = \dfrac{\rho}{\epsilon_0}$$ $$\nabla \times \mathbf{E} = 0$$ Or equivalently, $\nabla^2 V = -\rho/\epsilon_0$ and then ...
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### Temperature dependence of resistivity in metals

We know that in high temperature, resistivity in metals goes linearly with temperature. As temperature is lowered, resistivity goes first as $T^5$ due to "electron-phonon" interaction, and then goes ...
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### When two spheres of equal charge make contact, why does the larger sphere gain more charge?

Suppose that two spheres, $S_1$ and $S_2,$ with radii $R_1$ and $R_2$ resp. have the same uniform charge $Q$ and $R_1 > R_2.$ After they are forced to come in contact, why does $S_1$ gain more ...
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### Voltage as electromotive “force”

Considering the "water analogy" for electricity, it seems voltage is sort of like gravity: (image source: http://learn.olympiacircuits.com/electricity-flows-like-water.html) Now when water actually ...
11k views

### Why is the electric field inside a conductor zero in equilibrium?

My textbook says the field inside a conductor must be zero in order for the system to be equilibrium and therefore there must be no excess charge inside. Their proof: 1) Place a gaussian surface ...
19k views

### If the current is increased, is there more charge flowing or is it moving quicker?

Problem Current is the amount of charge that is flowing through a component per unit of time. For a given voltage, Ohm's law tells us that if we increase the resistance, then the current must ...
635 views

### Why do the charges on a parallel plate capacitor lie only on the inner surface?

In most pictures I've seen of parallel plate capacitors, charges are drawn so that they're entirely on the inner surface of the plates. I accept that there can't be any net charge within the ...
17k views

### Can a salt water solution conduct electricity forever? [closed]

We know that very pure water does not conduct electricity, but salt water is a decent conductor. This is commonly explained by saying that "the ions carry the current through the solution", an ...
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### Grounding system of conducting plates

So, I always make mistakes on problems such as this (the grounding part), so I'm hoping someone could really explain to me how the process works. There are $n$ large parallel plate conductors ...
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### How do bits get transferred over a copper wire?

I've been a programmer for a while, and I've done a little bit of network programming, but I'm wondering, how do bits get transferred over a copper wire? What counts for a 1 & what counts for a 0?...
710 views

### Shouldn't resistance only affect the kinetic energy of an electron?

Suppose a ball is falling from a high point and we stop it midway using a plank. Now the plank only affected the KE and total energy of the ball but not its PE. The same way, resistance is a ...
1k views

### Why does my measured I-V curve for a film of aluminum suggest high resistance?

I plotted the I-V curve between two points (few microns apart) on a thin aluminum film. I expected this metal to be a conductor and have a much lower resistance, but the slope suggests that it is ...
796 views

### From where do electrons gain kinetic energy through a circuit?

Supposing an ideal wire, How do electrons accelerate and gain kinetic energy? What I understand: When a circuit is opened ,electrons are crowded at the negative term of the battery and have high ...
2k views

### Work done by magnetic field on current carrying conductor

Suppose a wire of length L carrying a current I is kept in a uniform magnetic field B perpendicular to the current. The force on the wire will be IBL and work done by magnetic force when wire moves a ...
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### 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: ...
1k views

### Can a positively charged conductor have negative surface charge density somewhere?

This is a simple question that occurred to me while thinking about electrostatics. Let's consider a positively charged isolated conductor in equilibrium. In general, the surface charge density varies ...
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### 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 ...
1k views