# Tagged Questions

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

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### Effects of a Coiled Cable

Okay, I've got a little bit of a layman's question here. We're doing a bit of spring cleaning in our office and we've found a cabinet with boxes upon boxes of stored wires, so naturally, this ...
707 views

### How can a portable 5V battery charge another 5V battery?

For a device that is portable and can charge an iPhone 4 or Nintendo 3DS: http://www.amazon.com/New-Trent-iCruiser-IMP1000-Blackberry/dp/B003ZBZ64Q I wonder, if this device outputs 5V, and iPhone or ...
274 views

### Equation for finding electrical resistance

I want to know how the flow of electrons will change when I change the tempertature from 100 F to 250 F in a silicon semi-conductor (ex: computer mouse) How can I find this out?
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### Current against the inverse of resistance graph, $I = V/R +c$

If I have a plot of current ($y$ axis) against 1/Resistance ($x$ axis). The circuit it is measured from is a simply 2 resistors connected in parallel to battery, where the potential across the ...
4k views

### 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. ...
742 views

### Why are $\mu_0$ and $\epsilon_0$, which appear in electrostatics and magnetostatics, related to the speed of light which appears in electrodynamics?

$\epsilon_0$ and $\mu_0$ appear in electrostatics and magnetostatics. When we include time varying fields we have electrodynamics and the appearance of c which turns out to be related to $\epsilon_0$ ...
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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 ...
10k views

### Why is the charge naming convention wrong?

I recently came to know about the Conventional Current vs. Electron Flow issue. Doing some search I found that the reason for this is that Benjamin Franklin made a mistake when naming positive and ...
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### Is there something like the Poynting vector for hydraulic circuits?

The Poynting vector is a representation of the energy flux in electromagnetics, showing the amount and direction of power flow at different points in space. In electric circuits, the energy is not ...
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### Does power from a resistor perform work or heat transfer?

Let's say I have a cylindrical piston filled with air and fitted with an electrical resistor. The resistor has a current going across it and a voltage for a certain amount of time. My system would be ...
1k views

### Total Resistance of Infinite Resistor Grid?

The problem of the infinite resistor grid is very common. The solution for the resistance between any 2 nodes in an infinite resistor lattice is all over the internet. My question is somewhat similar ...
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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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### domestic electric AC wiring - Live and Neutral correct or not? [closed]

On electric circuits, with $120$ or $230$ AC mains, there are the wires Live and Neutral. The wiring isn't symmetrical : following the circuit, you cannot switch $L$ and $N$. However, in Italy, ...
9k views

### What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)?

This is a confused part ever since I started learning electricity. What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)? All of them have ...
1k views

### How does the X-Y mode of an oscilloscope work?

I recently used an oscilloscope in X-Y mode to draw the phase ellipsis of two voltages. I then used the formula phi = arcsin(2y/B) where y is the value of the ellipsis at x = 0 and B is the total ...
29k views

### What is the relationship between AC frequency, volts, amps and watts?

In an alternating current, how are frequency, voltage, amperage, and watts related? For instance, imagining the power as a sine wave, what is amperage if voltage is the amplitude? Is there a better ...
562 views

### How to teach the concepts of “Electric Potential” & “Potential Energy” to 10th grade students

I've got to teach the concepts of "Electric Potential" & "Potential Energy" to 10th grade students. I don't understand how to express these things and make them understand. “If you can't ...
4k views

### When does voltage drop occur?

Why or when does it occur in a circuit? What does it imply when you speak of a voltage drop across a resistor? (Obviously, it probably means that the current's voltage before the resistor is higher ...
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### Would a generator in vacuum/space provide electricity endlessly?

At it's simplest, electricity generation is achieved by induced voltage due to a changing magnetic field. In a vacuum in the absence of friction, would the initial spin imparted to the rotor of a ...
192 views

### Schottky and shot noise

I am looking for a little history on shot noise: when was it first predicted and first measured? In particular, what was the role of Schottky? His 1918 paper "Über spontane Stromschwankungen in ...
280 views

### Circuit Simulation

I am making a circuit simulation program, and I am not sure how to simulate the behavior of Diodes. Take this circuit: ...
1k views

### 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, ...
623 views

### Electrostatics:Basic question on electric current

I've got two questions for you. Electric current is the flow of electrons across a conductor.Why has it always got to do with electrons and not with protons? (I know neutrons are not eligible for ...
2k views

### 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 ...
350 views

### How to measure faster than light electric energy?

According to relativity,nothing can break light barrier.But a recent preprint shows energy transmission of commercial electric power (f=60Hz) is faster than light. (It is not the drift velocity of ...
931 views

### Why are downed power lines dangerous?

A friend of mine was telling me about a storm that knocked down a power line over at their place, and it got me to thinking. Why are downed power lines dangerous? I don't see any good reason for it. ...
208 views

### Introducing emf of a chemical cell as a hint towards quantum mechanics

Today I had a discussion with a colleague who teaches electricity and magnetism to 2nd year undergraduate physics students. He is seeking the best way to explain how is the emf generated inside a ...
2k views

### How can two different 12V batteries have different amperage for same resistance?

My local car parts dealer presented me his inventory of car batteries. One 12V battery had a 'cold crank amperage' of 600amps. The other 12V battery had a 'cold crank amperage' of 585amps. ...
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### Practical physics: where does this current come from?

It's been a while since school and I don't remember the right laws and formulas. So I come here. :) I've got a power cord extender running from the wall outlet to my washing machine. It's about 3 or ...
169 views

### What's the second terminal in corona discharge?

I don't get corona discharge. There's an electrode (say naked high-voltage wire) and a current develops from that wire and ionizes gas (air) on its way. But where does this current go? What's the ...
2k views

### How to calculate the exit velocity of a coil gun projectile?

First off, what quantities need to be factored in? Voltage and current through the coils, the magnetism of the projectile, the magnetic fields, etc.? Next, how would you calculate the speed of the ...
5k views

### What happens if a wind mill rotates in opposite direction?

Suppose if a windmill is made torotate in clockwise direction and due to air flow if it rotates in anti clockwise direction then does it produce electricity?
22k views

### Charging 12V 150Ah battery

I want to charge a 12V battery of 150Ah with a solar panel. The solar panel specs is 12V, 25 Watt. Can anyone please provide me how to calculate that how much time it will take to charge the battery? ...
369 views

### number of electrons my laptop uses in a second

in order to confirm whether I understand the relation ship between amps, columbs and electrons I decided to try out the following. my laptop adapter's label reads 3.34 amps. I assume that: amps are ...
18k views

### Why do power lines buzz?

When near high tension power lines, particularly after a good rain, the lines themselves emit a buzzing noise. A similar noise can be heard coming out of the electric meters attached to my apartment. ...
156 views

### Why only one prong in the plugs are not showing response to tester pen?

I have 2 pin outlet for A.C current . Now when I connect a TV plug in that and when I touch one of the prongs with my tester, the tester is showing response. But on the other prong the tester shows no ...
82 views

### Resistance from voltage and charge [closed]

I'm sure this is pretty basic, but I'm not very good at electricity. At both ends of a conductor we apply 12 volts. For one minute an electric charge of 72 C passes through the conductor. What is ...
1k views

### Total power consumption of electric device

For some electric devices, like a fan or air conditioner, I read about their power consumption in watts on their specification guide. Does it tell about the power at normal or full speed? or Does the ...
4k views

### Why is electricity not transmitted wirelessly?

Why is electricity not transmitted wirelessly such that we don't need to span cables on the earth's surface? As in: electricity is transmitted wirelessly from the power plant to the household.
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### Calculating time for a fully charged UPS

I have a UPS of 1000 Volts connected with 2 batteries each of 150 Amp. How much time it will take to consume the whole UPS (after fully charged) when a device of 1Amp is getting electricity form that ...