The study of the presence and flow of electric charge. Charges, currents, fields, potentials.
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A circuit with no voltage difference, but current flowing
From Michael on Skeptics Stackexchange:
How about a wire that's grounded?
Safe to touch, right? WRONG.
...
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3answers
576 views
Why is AC more “dangerous” than DC?
After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...
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371 views
Are square wave really square or are they always relative approximations using harmonics
I'm studying the properties of waves through different mediums, and got hung up on this.
Is a square wave always a sum of harmonics or can we produce a square wave by quickly changing voltage? Is ...
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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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5answers
573 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 ...
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3answers
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Is there a travelling speed of for electric field? If yes, what is it?
Consider a conducting wire of 1M and 1000KM. Now if we connect a battery and a bulb to both these wires. Bulb glows instantaneously its because (my guess:) electric filed travels from positive ...
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6answers
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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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3answers
229 views
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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6k views
Why can electricity flow only in one direction through a diode?
A few days ago I was soldering a small thing which contained a diode, a battery and some other useless things.
Unfortunately, I soldered the diode reversed and it didn't work. When I reversed it ...
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3answers
4k views
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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3answers
143 views
If an electric car were to drive without having to stop, would the range be greatly affected by the speed at which the vehicle is moving?
Of course aerodynamics factors into this question, and the faster you are moving the more air you have to push out of your way, the more energy you use. But would the difference be only a small ...
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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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201 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 ...
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2answers
325 views
Why do physicists believe protons and electrons are present in equal numbers?
I tended to consider that negative and positive charges are present in equal numbers in the universe to be a known, obvious fact. But is it so? How can we rule out the possibility that there is some ...
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5answers
485 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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1answer
195 views
why sometimes touching old flickering tube lights starts them properly
In my old house there are two old tube lights. Some times they don't start properly, (specially at evening time, may be it is because of low voltage), they starts flickering i.e. on and off ...
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1answer
111 views
How can there be a path to ground with thick shoes and a carpet?
I'm connecting a test light to one pin of an halogen lamp. When I touch the metallic part on the back of the test light, the light glows, as it is supposed to. However, I have thick shoes and I am ...
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2answers
2k views
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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1answer
310 views
Balloon rubbing; where do the electrons go?
If you rubbed a balloon with a towel, where would the electrons go: the balloon or the towel? Why?
I'm guessing the electrons would go to the object with a larger mass, but it's just a guess. :)
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2answers
496 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 ...
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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 ...
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1answer
70 views
maximum positive electric charge of solid body
What are the limiting factors on the positive charge of a solid body? If I assume a 'perfect insulator' environment that would not exchange charge with my solid body, I would guess that I can remove ...
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1answer
949 views
How to know what materials are good conductors of electricity?
I'm not asking a question like "Is the wood conductive?". No. I'm asking what properties do they have to have to be good conductors. Theoretically I mean. Thanks.
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3answers
460 views
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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3answers
226 views
How electricity, and generating electricity works on the atomic level?
I am trying to understand the basics physics as to how electricity works.
Unfortunately it seems most online material is either complex full blown mathematical equations, or water pump analogies.
I ...
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1answer
115 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 ...
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1answer
60 views
Thermal conductivity affected by electrical current
Does anyone know of any materials whereby the thermal conductivity can be changed by passing an electrical current through the material?
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322 views
How to calculate required current and specifications for a “wet coil” to generate x Tesla of magnetic field?
A water management project requires a "wet coil" (coil will be submerged in aqueous media) designed to generate a steady-state electromagnetic field of adjustable magnetic magnetic flux density at the ...
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1answer
679 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?
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2answers
297 views
Algorithm of Lightning Strikes?
Given an array of charge for a given area (2D or 3D), what algorithm would describe the path that lightning takes?
An example algorithm would be from the highest charge of the cloud, find the lowest ...
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3answers
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Why and how exactly is electric motor torque limited?
Inspired by this question and specifically this answer to it.
From my experience there's always some very specific limit to how much torque an electric motor can output. For example, an electric ...
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1answer
90 views
Superconductors and electrical fields
I have been looking around to figure out how superconductors are made. What ways are there to create a superconductor that don't involve a coolant like liquid nitrogen? Is it possible to cause a ...
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2answers
650 views
What is the source of high-frequency squeal in faulty CRT monitors and TV, and what is physics of generating this sound?
Sometimes old faulty CRT monitors generate nasty high-frequency squeal sound. What element might be responsible for generating such sound? I have heard that it might be dry electrolytic capacitor; ...
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1answer
590 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 ...
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2answers
355 views
lifetime of a PN junction in a diode
diodes are made of silicon, which have been enriched in phosphorus and boron to create the PN junction. Since the electrons are always going in the same direction, from N to P in the junction, I was ...
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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 ...
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2answers
502 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.
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Will adding heat to a material increase or decrease entropy?
Does adding heat to a material, thereby increasing electrical resistance in the material increase or decrease entropy?
Follow up questions:
Is there a situation were Heat flux ie. thermal flux, ...
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5answers
924 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 ...
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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 ...
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1answer
75 views
Can Earth's Magnetic Field Create Electricity?
If the earth has a magnetic field, can it, in theory, be run through a conductive metal coil to create electricity?
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254 views
How can you have a negative voltage?
How can you have a negative voltage? I don't really understand the concept of negative voltage, how can it exist?
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2answers
453 views
Derivation of Ohm's Law
Is it possible to derive Ohm's law (perhaps in some appropriate limit) from Maxwell's Equations?
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2answers
544 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 ...
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1answer
54 views
Why does the comb attract the pieces of papers if they're neutral?
When we rub our hairs with a comb, and then try to attract small pieces of paper, they're attracted by the comb. The pieces of the paper were not electrified before they were attracted. Then they ...
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420 views
Capacitor circuits with light bulb
Let's say we have a normal circuit with a light bulb, with wires and a battery.
When one places a capacitor in this circuit, how is the light bulb able to light up, even when the capacitor prevents ...
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3answers
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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 ...
3
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1answer
101 views
Is it possible to get energy from electrical wire using induction?
Pardon me if this is a stupid question but my physics courses are from a long long time ago and I was a teenager back then. ;)
Electricity in a wire generates electromagnetism, right?
Would it be ...
