The study of the presence and flow of electric charge. Charges, currents, fields, potentials.
23
votes
9answers
3k views
Can Maxwell's equations be derived from Coulomb's Law and Special Relativity?
As an exercise I sat down and derived the magnetic field produced by moving charges for a few contrived situations. I started out with Coulomb's Law and Special Relativity. For example, I derived the ...
22
votes
3answers
848 views
Wind generators - why so few blades?
Why commercial wind generators usually have just 2-3 blades?
Having more blades would allow to increase power OR decrease diameter.
Decreased diameter would also reduce stress due to different wind ...
20
votes
6answers
4k views
Lightning strikes the Ocean I'm swimming in - what happens?
I'm swimming in the ocean and there's a thunderstorm. Lightning bolts hit ships around me. Should I get out of the water?
19
votes
5answers
5k 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.
...
16
votes
4answers
2k views
Why do 'dead' batteries work again after exchanging the places of the batteries in an electronic device?
My camera, which is powered by two AA batteries in series, would not power on. I removed the batteries, exchanged their locations, and the device worked again - for another 15 minutes or so.
The ...
16
votes
1answer
532 views
Can lightning be used to solve NP-complete problems?
I'm a MS/BS computer science guy who is wondering about why lightning can't (or can?) be used to solve NP complete problems efficiently, but I don't understand the physics behind lightning, so I'm ...
14
votes
2answers
1k views
Why don't electric fish shock themselves?
Fish like electric eels and torpedoes have specially designed nerve cells that allow them to discharge hundreds of volts of electricity.
Now, while pure water is usually nonconductive, the dissolved ...
11
votes
5answers
1k views
How can Ohm's law be correct if superconductors have 0 resistivity
Ohm's law states that the relationship between current ( I ) voltage ( V ) and resistance ( R ) is
$$I = \frac{V}{R}$$
However superconductors cause the resistance of a material to go to zero, and ...
11
votes
6answers
2k 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.
11
votes
4answers
2k 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 ...
11
votes
3answers
415 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 ...
11
votes
2answers
2k views
Why do grapes in a microwave produce plasma?
Some of you may know this experience (Grape + Microwave = Plasma video link):
take a grape that you almost split in two parts, letting just a tiny piece of skin making a link between each half-part.
...
11
votes
2answers
661 views
Does Fire Conduct Electricity? Why?
Recently, I have stumbled upon a YouTube video by Veritasium describing the conductivity of fire. My question is: how exactly does fire conduct electricity? I am a high school student; therefore ...
10
votes
10answers
3k views
Does 'electricity' have mass? Is 'electricity' tangible?
Background: I'm in a legal academic discussion about the status of electronic 'goods' and whether they qualify as 'goods' in the same way a chair and a pen do. In this context (and specifically at the ...
10
votes
3answers
1k views
Is it possible to mathematically derive the formula for resistance?
Resistance is given by $\rho L/A$, where $\rho$ is the material constant, $L$ is the length, and $A$ is the area.
Is there any way that this can be derived mathematically, or is the only way ...
10
votes
4answers
2k views
Why can different batteries with the same voltage send different currents through the same object?
According to an answer in this thread on Skeptics:
If you take one of the little 12V
garage door opener batteries and short
out (directly connect) the two
terminals with a piece of wire or
...
10
votes
1answer
421 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 = - ...
9
votes
3answers
304 views
Current in a simple circuit
I was going over my notes for an introductory course to electricity and magnetism and was intrigued by something I don't have an answer to. I remember my professor mentioning, to the best I can ...
9
votes
5answers
935 views
Can someone explain the science behind MIT's 230% efficient LEDs?
I was reading Gizmodo the other day and I didn't quite understand the Physics behind this. Could anybody shed some light on how this effect actually works?
9
votes
2answers
6k views
How does load affect frequency on the power grid?
This story about the use of battery/freewheel based Frequency Regulators confused me about how the 60hz frequency of the North American power grid was set--saying that it was kept at that frequency by ...
8
votes
3answers
2k views
Why do power lines sag when they are heated up?
I was reading some information about the 2003 power blackout in the Northeastern US.
Beginning early in the afternoon of August 14, 2003 big transmission lines began to fail in First Energy's ...
8
votes
8answers
7k views
Electricity takes the path of least resistance
Is this statement correct?
If so, why is it the case? If there are two paths available, and one, for example, has a resistor, why would the current run through the other path only, and not both?
8
votes
8answers
3k views
What is the difference between electric potential, voltage and electromotive force?
This is a confused part ever since I started learning electricity. What is the difference between voltage and electromotive force (emf)? Both of them have the same SI unit, right? I would appreciate ...
7
votes
3answers
1k views
How do you produce electricity from a wind mill?
How does a spinning windmill produce electricity?What is the principle behind the windmill?
7
votes
1answer
893 views
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 ...
7
votes
3answers
678 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, ...
7
votes
2answers
785 views
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 ...
7
votes
2answers
473 views
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, ...
6
votes
6answers
6k views
How to avoid getting shocked
sometimes I get "charged" and the next thing I touch something that conducts electricity such as a person, a car, a motal door, etc I get shocked...
I'm trying to avoid this so if I suspect being ...
6
votes
6answers
9k views
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 ...
6
votes
5answers
433 views
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 ...
6
votes
2answers
237 views
Conservation of Energy in a Capacitor
Consider a parallel-plate capacitor in free space. A negatively charged point particle with initial velocity $v$ passes through the space between the pair of parallel plates (with an initial path ...
6
votes
1answer
614 views
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 ...
6
votes
2answers
193 views
Ionized Depletion Region, Why aren't those charged being excited?
Ok so I understand the PN junction, and how when 2 Semiconductor materials are placed together the Electrons will jump into the Holes near the junction creating a Negatively Ionized Atoms on the ...
6
votes
2answers
1k views
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 ...
6
votes
3answers
791 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 ...
6
votes
1answer
195 views
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 ...
5
votes
5answers
986 views
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 ...
5
votes
4answers
5k views
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 ...
5
votes
4answers
2k views
Resistor circuit that isn't parallel or series
What's the equivalent resistance in this circuit (between points A and B)?
5
votes
3answers
411 views
Can electricity transfer radioactivity?
If a cable used to power something is exposed to a radioactive source will it over time make the entire cable radioactive?
5
votes
4answers
536 views
Help fill in my understanding of the Polywell fusion reactor
Polywell is a proposed new type of fusion reactor, which is designed to use magnetic fields to overcome the problems with the Elmore-Tuck-Watson fusor. I'm trying to understand exactly how it works.
...
5
votes
5answers
684 views
How long would it take for electricity to flow from one terminal to other, via a 1 LY long wire?
Basically, how long does it take for electricity to determine there is a closed circuit and how does it know that the circuit exists? I'm curious to know how it knows there is a closed circuit at any ...
5
votes
2answers
1k views
how calculate resistance between two points for arbitrary resistor grid?
I need to calculate resistance in an electrical grid.
Grid is a graph. Edges of a graph are resistors. How calculate resistance between any two vertexes for arbitrary graph?
I know Kirchoff law and ...
5
votes
2answers
453 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 ...
5
votes
4answers
1k views
How do electrons “know” to share their voltage between two resistors?
My physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people ...
5
votes
1answer
591 views
Salt water conduction
Does salt water conduct mostly by the ions travelling through the solution, or by electrons collectively flowing or hopping through the solution like in metals?
5
votes
2answers
160 views
What's the difference between Capacitors, Ultra-Capacitors and Batteries
Capacitors are known to hold and release energy very quickly, unlike the slower release that batteries exhibit. If one were to bunch many (1000's of) capacitors together could they function as a ...
5
votes
2answers
292 views
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 ...
4
votes
5answers
333 views
This sentence makes no sense, electrostatics and electrons moving in a conductor - current
I highlighted the part where the confusion is.
The sentence said that the potential difference is 0, yet it then immediately talks about how electrons can have motion.
What are they trying to ...
