# Questions tagged [electricity]

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

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### Surface charge in a wire?

The image above shows the distribution of the surface charge in a current carrying wire. The surface charges distributes themselves to make sure the field inside the wire is always perpendicular to ...
11k views

### Why do lightning rods have a sharp point at the top?

We know that a lightning rod or lightning conductor is a metal rod or metallic object mounted on top of an elevated structure and, if we look closely, most of them have a sharp point at the top. What ...
2k views

### How did physicists know that only negative charges move?

I have phrased similarly another question about how physicists knew that two charges exist, positive and negative. The purpose of the question is not necessarily to educate me historically. It's just ...
5k views

### Why are materials that are better at conducting electricity also proportionately better at conducting heat?

It seems like among the electrical conductors there's a relationship between the ability to conduct heat as well as electricity. Eg: Copper is better than aluminum at conducting both electricity and ...
40k views

### What happens to capacitor’s charge when the plates are moved further apart?

In my physics textbook there is an example of using capacitor switches in computer keyboard: Pressing the key pushes two capacitor plates closer together, increasing their capacitance. A larger ...
24k views

### Why does it spark when I push a plug in the electrical socket?

When I slowly push a plug into the electrical socket I can often see sparks. Can anybody explain why? Can this be possibly harmful for the devices I plug in?
595 views

### computer vs heater coil comparison

If I have a computer and a heater coil that consume exactly the same amount of energy, which would be more efficient at heating my room? This is assuming that they both have the same fans and heat ...
2k views

### How is Kirchhoff's voltage law understood in the water flow analogy?

I met the Kirchhoff circuit laws in the past, but now I'm trying to associate them with a practical representation to be sure to understand them. Let's start with the Kirchhoff current law: If I say ...
1k views

### What happens if you connect a hot resistor to a cold resistor?

Kind of an extension to this question: If you heat up an object, and put it in contact with a colder object, in an ideal insulated box, the heat from one will transfer to the other through thermal ...
188 views

### Are emitters always receptors?

I had a teacher who told us that every emitter, at least electric powered, can also behave as a receptor. Then he gave us examples of devices producing current : - LEDs when put under a light - ...
2k views

### Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?

The video High power line workers shows linemen servicing a live high voltage transmission line. As the helicopter approaches the line, the lineman reaches out with a metallic wand that is ...
341 views

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### Why does resistance increase with length?

This is for the case of wires only (pipes are easy). I see that if I place a 9-Volt (constant) battery across any wire, the current is proportional to resistance. I don't understand why, for a ...