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 ...
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 ...
4
votes
1answer
163 views
Impurity scattering temperature dependence
Is there any temperature dependence of relaxation time in impurity scattering of conducting electrons? It seems to me that there is none. But, some people claim that there is.
So if you could ...
3
votes
3answers
4k views
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 ...
3
votes
2answers
541 views
Relating milliampere-hours to watt-hours for batteries
I've seen many batteries that are measured in milliampere hours (mAh), while others are measured in watt hours (wh). How can I convert them between each other so that I can actually compare them? It's ...
3
votes
6answers
3k views
What causes an electric shock - Current or Voltage?
Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - ...
3
votes
5answers
917 views
Can the lightning be captured and used as power source?
I would like to update my knowledge in this area, that is really out-of-dated and stopped somewhere like ten years ago.
I asked the very same question on my physics lecture at my studies and got the ...
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 ...
9
votes
3answers
303 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 ...
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 ...
3
votes
1answer
322 views
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 ...
2
votes
4answers
2k views
Understanding the relationship between electricity and magnetism
I keep on hearing that magnetism is just another form of electricity and vice versa. If that's the case why can't we use magnets as batteries, and why aren't my batteries magnetic?
8
votes
5answers
913 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?
5
votes
5answers
984 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 ...
11
votes
2answers
656 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
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 ...
4
votes
6answers
6k views
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 ...
2
votes
1answer
334 views
Can energy be extracted from clouds?
Can cloud charge imbalance be used as an energy source?
First off quite some energy must be present in clouds: a lightning path is quite long, and electrical breakdown of air requires about 1MV/m. ...
6
votes
1answer
611 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 ...
4
votes
1answer
114 views
How much of current flows through a bird sitting on a power line?
I've been googling for hours and went through over a hundred answers. Now, some say the bird doesn't form a closed loop, some say the current is so small that it doesn't kill the bird. From as much as ...
4
votes
2answers
199 views
How does lightning “know” where to go?
If lightning comes down in, say, a large flat field with a lightning rod sticking out of the middle, the lightning will strike the rod.
How does it "know" the rod is there?
Will it always strike the ...
4
votes
2answers
244 views
Sum total distance of electrons on a spherical surface
What is the sum total distance between every possible pair of point charges when there are n point charges on a spherical surface?
All point charges can only and are located on the infinitesimal ...
1
vote
3answers
82 views
Capacitor Charging and Discharging when connected to the ground
When we charge a capacitor using a battery and then remove the battery, the plates of capacitor becomes charged. One holds positive charge and the other one gets equal negative charge. o. k. ?
Now ...
1
vote
1answer
2k views
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 ...
2
votes
2answers
2k views
Would you die if you put your hands on a powerline?
You know how birds perch on powerlines without getting electrocuted? What if by some chance that I find myself falling and I grab on one of them? Let's say both of my hands are on the same line, would ...
1
vote
2answers
142 views
Relativistic charge density contraction in a closed loop
I have heard that magnetism is a relativistic effect of electricity. The law says that charge is conserved, only distances are shrunk. So, I cannot add more charge to increase density. When we have an ...
0
votes
3answers
9k 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? ...
22
votes
3answers
843 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 ...
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 ...
4
votes
1answer
583 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 ...
2
votes
1answer
191 views
Could we build a super computer out of wires and switches instead of a microchip?
I thought of this question; would too much wiring make a computer burn down? Or can you build an actual full-speed supercomputer computer using switches and wires?
In other words, could simply adding ...
2
votes
5answers
435 views
Why doesn't an electron accelerate in a circuit?
Why don't electrons accelerate when a voltage is applied between two points in in a circuit? All the textbooks I've referred conveyed the meaning that when an electron traveled from negative potential ...
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.
...
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?
5
votes
2answers
452 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 ...
4
votes
5answers
572 views
What voltages are used to “safely” shock someone (as in a carnival game)
I've had this debate with some coworks. What voltage (rough order of magnitute) is used to safely shock people?
"Safe" is a vague term, but as an example, there are arcade games where you hold onto ...
4
votes
4answers
2k views
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 ...
3
votes
1answer
807 views
How can a conductor be grounded yet there are induced charges on it?
A classic example for the method of images is the following, quoted from Griffiths's Introduction to Electrodynamics, page 121:
"Suppose a point charge $q$ is held a distance $d$ above an infinite ...
2
votes
2answers
120 views
What are the current possibilities for large-scale storage of electrical energy?
I'm curious as to how large-scale electrical storage is managed now, how much they can store, how well they scale and for how long (and what is their loss rate).
(I'm not asking about technological ...
6
votes
5answers
431 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 ...
3
votes
1answer
374 views
General integral to find resistance
My question is: is there a simple and truly general equation for the resistance between two electrical equipotential surfaces?. Obviously, if so, what is it, and if not, why? It would be very ...
2
votes
5answers
1k 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. ...
2
votes
1answer
635 views
Current from induced emf
If the induced emf in a circuit is negative, and current from this emf is the emf over the resistance, what happens to the negative sign in the induced emf when solving for the current? Surely there's ...
0
votes
1answer
41 views
Charging Glass Rods
When we rub two glass rods with their respective pieces of silk cloth, the two glass rods would repel each other. What if we rub the glass rod against the other glass rod? Will they repel each other? ...
0
votes
0answers
57 views
Capacitors discharging in series [duplicate]
If you connect positive plate of a charged capacitor to ground, it doesn't get discharged. Now consider $4$ capacitors of equal capacitance connected in series to a $10\, \mathrm{V}$ battery. Connect ...
0
votes
1answer
214 views
Resonant inductive coupling and Schumann resonances
I was reading about WiTricity (http://en.wikipedia.org/wiki/WiTricity) a technology developed by MIT to wirelessly transmit electricity through resonance, and I have this question:
Given the ...
0
votes
3answers
430 views
Parallel or series connection?
Are C1, C2 and C3 connected in parallel, or C2, C3 in parallel and C1 in series with C23?
Btw it appeared as a question in the basic physics Albanian A-levels yesterday. You had to find the ...
0
votes
1answer
179 views
Tubelights+power lines pictures?
I've come across many pictures like these, sometimes in chain emails reporting the dangers of power lines.
Another claim is that they run on "wasted" energy.
The explanations given are that the ...
