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

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Where does the electricity, generated by a solar panel, go if you don't use the electricity?

I'm sorry if this question is too trivial for this Q&A forum. I am a layman when it comes to physics (though I did cover the high-school physics courses). I was wondering what happens to the ...
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Why do charges enter the capacitor in the first place?

I have been studying Capacitors for the past year now and the one thing I don't understand is how a charge is stored on the capacitor. Essentially, a circuit with a capacitor is an incomplete circuit ...
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648 views

Explanation for speed of an electrical impulse

Our calculus book, Stewart, has a problem where they claim that for a metal cable (inner radius $r$) encased in insulation (outer radius $R$), the speed of an electrical impulse is given by $$v = - ...
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How electrons move so fast in a electric circuit?

Whenever we switch on a bulb......it takes almost no time to glow up.....But we know that the atoms of a solid are tightly packed and there is a very little space between them. So how the electrons ...
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Resistor circuit that isn't parallel or series

What's the equivalent resistance in this circuit (between points A and B)?
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What happens when we connect a metal wire between the 2 poles of a battery?

As I remembered, at the 2 poles of a battery, positive or negative electric charges are gathered. So there'll be electric field existing within the battery. This filed is neutralized by the chemical ...
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Why does lightning emit light?

What exactly is causing the electric discharge coming from the clouds to emit light while traveling through the air. I've read and thought about it a little but with my current knowledge I cant really ...
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Why do birds, sitting on electric wires, not get shocked?

If we would touch electric wires, we would get a shock, even if we are not touching ground (so that no connection is complete form wire to ground through us). I always see that birds sit on electric ...
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What causes fluorescent light bulb to light up when it is near a plasma globe? Can this phenomenon be used to generate electricity in a circuit?

When a fluorescent light bulb is placed near a plasma globe, despite the fact there isn't a closed circuit, a part of the light blulb would light up. I tried measuring the voltage of the air ...
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Relativistic drift velocity of electrons in a superconductor?

Is there a formula for the effective speed of electron currents inside superconductors? The formula for normal conductors is: $$ V = \frac{I}{nAq}$$ I wonder if there are any changes to this ...
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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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How can one derive the Ohm's Law?

I am looking for the derivation of the Ohm's Law i.e., V is directly proportional to I. Can someone help me with it?
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Is electricity instantaneous?

My question is basically what exactly is electricity? I've simply been told before that it's a flow of electrons, but this seems too basic and doesn't show that electricity is instant. What I mean is ...
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Intuitive definition of electromagnetic field

I am curious about the following: Checking about what is an EM field in wiki it says: An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged ...
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Why does my wife's skin buzz when she's using her laptop?

When my wife uses her laptop, if I touch her skin, I can feel a buzz. She doesn't feel the buzz, but she can hear it if I touch her ear. So I'm guessing it's a faulty laptop, and she's conducting an ...
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Is a signal traveling through fiber faster than a signal traveling through copper?

Does the transmission medium affect the speed of a signal? For instance does light traveling through a fiber cable get a bit from A => B faster than copper can transmit a bit the over the same ...
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Tesla coil arc in air - where is it going?

here is a picture of a Tesla coil with a discharge that seemingly terminates in the air. What completes the circuit at the end of the streamers?
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Why does a glass rod when rubbed with silk cloth aquire positive charge and not negative charge?

I have read many times in the topic of induction that a glass rod when rubbed against a silk cloth acquires a positive charge. Why does it acquire positive charge only, and not negative charge? It ...
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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?
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How do electrons know when a circuit is closed?

I was told that electrons do not begin flowing unless the circuit is closed. The electrons from the battery are not in the ends of wire when it is open, apparently, as there is no reason for them to ...
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Why is electrical energy so difficult to store?

Does anyone know a general answer to these questions? (I've asked them together because they're all pretty related, it seems.) Why is it that we find electrical energy so difficult to store? Do we ...
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Desperately Need Help with Grade 9 Static Electricity

I am preparing to teach Grade 9 Static Electricity next week and am going crazy trying to figure out what is happening in one of my experiments. I have a short piece of PVC pipe, 4 inches diameter, ...
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473 views

Temperature and resistance?

Why does resistivity increase with temperature? The explanations I have heard so far are that increasing temperature increases vibrations in the lattice structure resulting in the number of ...
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Tying knots in power cables to prevent power surge from lightning strikes

There are plenty of references to this claim on the internet that tying knots in power cables will prevent a piece of equipment e.g. television or computer from a power surge. How can this be ...
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Why is electric current dangerous to humans? [closed]

How does a strong electric current harm our body? A strong electric current will posses a great charge. But how does that charge injure us?
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How are electric flux calculations not double integrals?

A disk of radius 0.10 m is oriented with its normal unit vector $\hat{n}$ at 30$^{\circ}$ to a uniform electric field $\vec{E}$ of magnitude 2000 N/C. What is the electric flux through the disk? ...
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In an alternating current, do electrons flow from the source to the device?

If electrons in an alternating current periodically reverse their direction, do they really flow? Won't they always come back to the same position?
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Which dissipates more power, a small or big resistor?

I was talking to someone about trying to dissipate the most heat from a metal crucible (essentially just a resistor $R$). He argued that you wanted the resistor to have a high resistance because ...
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What causes contact resistance?

When two components are combined in an electric circuit, there is apart from their own resistances a contact resistance at their junction. This causes a sudden voltage drop of ...
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Why were the SI base quantities chosen as such?

The reasons for choosing length, mass, time, temperature, and amount as base quantities look (at least to me) obvious. What I'm puzzling about is why current (as opposed to resistance, electromotive ...
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Difference between current and voltage sources

I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is ...
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Of all the electrical energy used in a home, is there any portion that won't eventually become thermal energy in the home?

Considering all of the appliances that the average home uses--microwaves, light bulbs, dishwashers, refrigerators--is it safe to say that all of the electrical energy in a home will be converted to ...
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How do you produce electricity from a wind mill?

How does a spinning windmill produce electricity?What is the principle behind the windmill?
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Why doesn't the electric field inside a wire in a circuit fall off with distance from the battery?

We studied electric fields due to point charges. The magnitude of these fields decreases with the square of the distance from the point charge. It seems to me that we could treat the positive ...
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Why does a salt solution conduct electrical current?

How does e.g. sodium chloride (aq) conduct electricity? By accepting electrons (unlikely since they already have a full outer shell)? But they can't be hopping around themselves, can they? I mean, if ...
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Can resistance be directional?

When we think of resistance, we always think of a scalar value associated with a piece of a material. After all, resistance is but resistivity times surface geometry. But can resistance be ...
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How can I prevent being zapped by static electricity every time I touch a doorknob or handle in the office?

I don't know what it is about this office, but it seems everything I touch (doorknob, bathroom faucet, edge of kitchen sink in the break room), I get zapped by static electricity. It's getting old. ...
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How do bathroom scales measure body fat percent?

My bathroom scale has 2 metal strips each for a foot and the producer claims that it can measure body fat percent. There is a warning in the manual, that if I have heart problems (I guess pacemaker), ...
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What's the source of electricity for the human brain?

I keep hearing that there's always electrical activity taking place inside the human brain. Our heart and various other organs function because it receives electrical signals called impulse. But, ...
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What happens to a fully charged battery, when you continue to charge it?

If I leave my cell-phone charging the whole night, it will be fully charged after a while. What happens with the battery and the excess energy I add? Also, I noticed my charger emitting a different ...
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What’s the relationship between thermal radiation and Johnson thermal noise?

All objects above absolute zero emit radiation due to random collisions between the atoms they are made of. The spectrum of radiation emitted varies according to the temperature of the object, I ...
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Why does electric field intensity $E$ can be uniquely determined by its divergence and curl? [duplicate]

My question is, the number of following equations $$\nabla\cdot E=\frac{\rho}{\varepsilon}$$ $$\nabla\times E=-\frac{\partial B}{\partial t}$$ is 4 while the number of unknown variables ...
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Where do electrons in electricity come from?

Where do the electrons come from when an electric generator is making electricity? Is from the air? Would a generator work in a vacuum? Electrons have mass so where would they be pulled from if ...
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Does Tesla's photoelectric “solar cell” really work?

Tesla patented a device for gathering energy from light, using the photoelectric effect. (US 685,957 - Apparatus for the Utilization of Radiant Energy): Basically just a sheet of "highly polished ...
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Why does a faraday cage protect you from high currents?

In an electrostatic case it is clear that that in a space enclosed with a conductor (without charge in it) the electric field is zero. This is often demonstrated in physics shows like on the ...
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When mutual inductance is occurring between two coils, is self inductance always occurring in each individual coil?

When a coil connected to an AC generator creates an EMF in another nearby coil (mutual inductance), is self inductance simultaneously occurring in both coils?
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What experiment disproved single fluid theory of electricity?

I just can't understand how history of electricity goes on. What experiment disproved Benjamin Franklin's fluid theory of electricity?
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Electrical force vs gravitational force

Given that the electrical force is so much stronger than gravitational force at atomic levels, why is it that it's the gravitational force between you and the earth that keeps you on the ground rather ...
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Why don't electric workers get electrocuted when only touching one wire? [duplicate]

I know that when electricians work on the poles on the streets, if they only touch one wire at a time they will be fine. However, from my understanding, the negative wire is connected to a large ...
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What happens if I throw a battery into water?

Today I have by accident thrown a AAA battery into a bucket of water. I fished it out of the water immediately (within 20 seconds or so) and nothing notable had happened and the battery is still full ...