New answers tagged electricity
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You say:
since electricity's displacement is very slow ?
I suspect you mean the electron drift velocity in metallic conductors is low, but that's completely different to the electron transport in a lightning bolt.
I'm not sure the mechanism of conduction in a lightning bolt is fully understood, but consider this. The dielectric breakdown of air ...
-1
My girlfriend and I were swimming in the ocean about 30 feet from a beach in Costa Rica as a storm was approaching. We saw occasional flashes of lightning, and I was counting the time it took to hear the thunder, which was at least 7-8 seconds at the fastest, and often 10 or more seconds. I figured as it was at least a mile or more away we were fine, but ...
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Studying the problem some, I think what your showing is superposition of a voltage source and a current source. In the first circuit, you've zeroed the current source (making it an open circuit), and in the second circuit, you've zeroed the voltage source (making it a short circuit).
In both cases, you appear to be trying to solve for the current through ...
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In reality you are not able to connect anything in parallel. There are always resistances and (for AC) capacitances and inductances that cause voltage drops. So connecting two sources will cause current flow from one battery with higher voltage to the other making a voltage drop on the wire. This current can be very high, but it is never infinite, as it ...
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Firstly, I am assuming these batteries to be DC, otherwise this solution is wrong:
If you connect multiple batteries to a circuit, their polarity makes all the difference. If they are opposite in polarity then the battery with lower voltage will charge. A diagram will help to elaborate the question if you are talking about a specific arrangement.
If the ...
1
It's hard to sure without the context, but I'd guess that the definition is given that way because all batteries have a non-zero internal resistance, $R_i$, so if a current $I$ is flowing the measured voltage is $E - IR_i$ where $E$ is the EMF of the battery. The measured voltage only equals $E$ when $I$ is zero i.e. no current is flowing.
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You can get resistivity of material by formula:
R = ρl/A
=>> ρ = RA/l
where R is resistance, A is area of crosssection and l is length of the wire
Put the values and u would get the answer.
5
Not really. A magnetic field alone doesn't create electricity. A changing magnetic field does. The Earth's magnetic field does change a tiny bit but not enough to really generate much.
The other option is to move the inductor in the magnetic field. The Earth's magnetic field is quite homogeneous over short distances though so the coil would need to move ...
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1, An ideal screw connection with a soft metal like copper gives an almost perfect metal-metal bond. There is a potential problem of corrosion and pollution forming and some people cut the ends of the wires and redo them periodically. Or use gold plated connectors and tinned wires.
2, No the resistance of a thin wire in series with the speakers will add to ...
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I got the access but I'm too sleepy to understand. Sorry. I will just throw a picture here. Hope I didn't violate any sort of copyright law. yawn
DO NOT COPY OR SPREAD THIS PICTURE. PLEASE DELETE THIS ANSWER IF THERE ARE ANY VIOLATION OF THE LAW. I'm a Chinese. I know no copyright thingy.
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I think it just refers to a massive body.
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You are probably asking the question because you haven't gotten to alternating currents yet. One typical and simple example I can think of is the AC-DC War, AC won because it uses very high voltage and very low amperage to transmit electricity, this leads to very low power loss, compared to DC transmission. Although I have heard extremely high DC ...
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Ok, let's consider $\vec{r} \vec{dr}$, it is equal to $|\vec{r}||\vec{dr}|_\vec{r}$ where $|\vec{dr}|_\vec{r}$ is projection of $\vec{dr}$ on $\vec{r}$. If you draw $\vec{r}$ and a small (remember, you need infinitesimal!) $\vec{dr}$ you will notice that this projection is actual equal to $|\vec{dr}|_\vec{r} = d|\vec{r}|$, so $\vec{r} \vec{dr} = ...
1
The voltmeter does indeed draw current, but very small. Its internal resistance should be high, unless it's a very cheap voltmeter.
Putting the voltmeter's internal resistance, let us say 1MOhm just to make up a value, in series with the battery's internal resistance of a fraction of one Ohm, makes a voltage divider providing practically the entire ...
2
why does the voltmeter not form a closed loop with the circuit and hence cause energy to be dissipated by internal resistance
It does, but the voltmeter probably has an impedance of 10,000,000 ohms - as most multimeters do - so the current flowing is negligibly small (0.6 microAmps) and therefore the voltage drop due to battery internal resistance is ...
1
There are two phenomena in your question.
(1) Let us first understand how magnetic field can be considered to "arise" because of relativity. Imagine a frame of reference in which a charge $Q$ is at rest. If another charge $q$ is brought in its vicinity, it will experience only an electrostatic force. Now get on to another inertial frame of reference moving ...
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Thermistor with this particular temperature behavior are commonly semiconductors. In a semi-conductor, there is an energy gap between the (filled) valence and the (empty) conduction band. At zero temperature, no charges are in the conduction band and the resistance should be infinite as the system behaves basically like an insulator.
If you turn on the ...
3
First off, what you describe only happens for highly amplified speakers. The current change when you touch the wires is pretty tiny and you'll only hear a sound when that signal is being amplified significantly before being sent to the speakers.
There are many reasons why a tiny bit of electric current flows from your body to the speaker wire so I'll only ...
1
You should not connect different batteries in parallel.
If you do, the battery with the highest voltage will discharge into the other one, until they end up with equal voltages. If the second battery (the lower voltage one) is a rechargeable, then it will be charged by the first one, again until the two have the same voltage. In this case the end voltage ...
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In ideal circuit theory, the parallel connection of two voltage sources results in an inconsistent equation, e.g., a 3V and 2V source connected in parallel, by KVL, gives the equation: 3 = 2.
In the real world, batteries are not ideal voltage sources; batteries can supply a limited current and the voltage across the battery does, in fact, depend on the ...
3
Our current understanding suggests that black holes can have electric charge, and that in addition to mass and angular momentum, these are the only ways that black holes can have distinguishable physical properties. This is a result of the famous no-hair theorem, although keep in mind that no definitive proof of this theorem yet exists.
As this wikipedia ...
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These are two separate questions. It's better if you don't try to combine two questions into one.
In answer to the first question, yes, a black hole can have a measurable charge. You measure it the same way you'd measure any other charge. This is all purely theoretical, however. Many real-life black holes have been observed and characterized by their ...
1
First, one additional point. It's not just $R_{copper}$ limiting current, but also the battery's internal resistance. This is modeled as one more resistor in series. For most small batteries you might get your hands on, it's less than one Ohm.
People playing with wire and low-voltage batteries don't get zapped because the resistance of Human, when ...
4
An ampere passing through your heart can give you a heart attack. An ampere passing through a wire will not.
The human body has a fairly large resistance ($10000\ \mathrm{\Omega}$ perhaps?), so the same voltage that can make a large current pass through a copper wire will not necessarily make any significant current flow through a person.
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The answer is YES, it is possible for current to flow in an open circuit. The only requirement is that the current be "alternating" current. A capacitor is essentially an open circuit, and alternating current will "flow" trough it.
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This isn't what you're asking, but it is possible for currents to flow in an open circuit. Even a plain old block of copper is an "open circuit", for instance, but you can induce eddy currents to flow in it by applying a changing magnetic field. In a regular circuit this effect would be very small, though, as the copper wires have small width.
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I was told in the paradox of conductor's neutrality that in addition to contraction, mentioned in the relativistic electromagnetism tutorials, the electrons of conduction experience an expanding force, when accelerated. The expansion factor is exactly Lorentz $\gamma$, which compensates the contraction. The net effect is that distance between electrons is ...
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You're confusing charge with voltage/potential. Objects have charge, voltage is measured between objects. If two objects have no charge, the voltage between them is 0. If two objects have the same charge, the voltage between them is still 0.
Voltage is always a relative difference between two points. When we say "Terminal A is at 5 volts", what we ...
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The net charge of any of those internally connected pairs of plates is always zero. That is, when you charge the capacitors, charge doesn't leave the wire between C and D, it only moves along it, and is held in place by the electric field of the adjacent plates. If a circuit is completed that allows charge to flow from D's negative plate to A's positive ...
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When you touch a hydro wire, and ONLY a hydro wire -- nothing else -- there's no potential difference across your body. Your entire body is at the same potential, which is that of the hydro line (often thousands of volts). This is why birds don't get electrocuted if their feet touch only one wire. Plenty of birds, particularly eagles, have been fried because ...
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AC or DC, you only get electrocuted if current passes through your body. (Current passing through any part of your body can be dangerous, and possibly cause an electrical burn, but current passing across your heart is the one that's really dangerous.) Touching just one wire at a time gives the current nowhere much to go. You are right to think that some ...
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electric current always takes the way which has the lowest resistance.
When the birds aren't grounded the electric current won't take the way through the birds.
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This is because the neutrality of polarity can be changed by electric field in this case. When you create - charge in the comb and you expose the pieces of paper to the electric field created by the charge, you will polarise them so that the part closer to the comb will be + and the other will be -.
Here, see the electric field. The same polarities do not ...
-1
I think your question is very relevant.
I think I can put it in a wider perspective.
In Minkowski spacetime when you close a loop interesting things happen.
I believe the ring configuration that you point out exposes a severe weakness in the usual exposition of magnetism-as-relativistic-side-effect-of-the-coulomb-force.
I will abbreviate this ...
1
There are many materials that can be charged by triboelectric effect. Tipicaly you can observe this effect rubbing a material like wool and amber.
The phenomenon is quite complex but it's in great part because the different electron affinity of the materials (one loses easily an electron and the other captures an electron).
1
charge inside the conductor moves with random speed which is known as thermal speed.
But average velocity made by the randomly moving charges is zero as they are not alined in the absence of external force i.e. voltage supply.
static electricity also termed as electrostatics creates electric field, static charges resides on outer surface of the conductor
1
For flow of charge, the circuit should be closed. In open circuit, no charge flows. If we connect both the capacitor plates it makes closed circuit, charge flows in the circuit, as a result charges on the plates neutralizes to zero.
If only +ve plate of the capacitor is only connected to ground there is no closed circuit. no charges flows from the ground.
...
0
since circuit is open no charge is shared. if the circuit is closed ie capacitors are connected by conducting wire then charge will be shared. charge would flow from higher potential to lower until they come to common potential.
In the given circuit no charge is shared and potential across both the capacitors remains same.
1
I think every fundamental definition is kind of going in circle.
I would say an electric charge is something that obeys Maxwell's laws.
But to write those laws, you have to know $\vec{E}$ and $\vec{B}$ which need a definition of an electric charge.
At the end you just group things that look/react alike and named them.
The problem arise when you have to ...
1
Practically, for a macroscopic body such as a chunk of metal, the charge on that body is the difference between the number of electrons and protons in the body. It is hard to knock a proton out (can be done, though), but for conductors we can push and pull electrons out by supplying a bit of energy (back to that in a moment). However, instead of saying the ...
1
When you run two different materials together you will usually transfer electrons from one material to the other. For example if you rub glass with silk the electrons transfer from the glass to the silk and you end up with positively charged glass and negatively charged silk. That's why the two glass rods repel each other: they both carry a positive charge ...
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What we mean here by the word stationary is that the (macroscopic) charge density is constant , even if charges are moving actually.(An explanation for the word macroscopic comes in the next paragraph). A famous example is a rotating sphere with charge density $\rho$ , which is (electrically) equivalent to a non-rotating sphere.(But has a magnetic field due ...
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Your question is the result of a poor wording choice by the Wikipedia author. While it may be possible to create a digital computer that makes use of AC power, none do. The power supply in modern desktop computers use a transformer and rectifier (and some capacitors for smoothing) to provide a constant, smooth $12\, \mathrm{V}$ DC current for the computer ...
0
To get shock the electrical current should pass through a body. Due to Ohm's law this current is directly proportional to the potential difference across the two points. Taking into account electrical resistance of the bird's body, the potential difference between its legs is much smaller than a potential difference between the wire and the ground. Here is ...
0
You need some background in electricity before you can understand this answer so please look at the link at the beginning of the sentence first.
The current running on the power line is in an electrical circuit . A generator has two wires: one provides the energy and carries the high voltage, and the circuit closes going back to the ground where the ...
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This formula is derived using conservation of charge principle and so it's valid for the superconductors as well. There's a critical magnetic field that above which a superconductor becomes normal conductor and it's a function of temperature.
If a large current is to pass through a superconductor, a magnetic field will be produced that disrupts ...
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Ohm's Law does not have a problem here any more than any other formula in the sciences which involves dividing by a denominator which can go to zero.
Ohm's Law exhibits a singularity when there is no resistance, but a nonzero voltage. An ideal voltage source cannot be connected in parallel with a zero resistance, because that implies that infinite current ...
5
Looking at your question from the perspective of ideal circuit theory, an ideal resistor has the following I-V relationship:
$V_R = I_R R$
The voltage across the resistor is proportional to the current through the resistor with constant of proportionality equal to $R$.
In ideal circuit theory, an ideal conductor can be thought of as a "zero ohm resistor". ...
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Ohm's law works for ordinary conductors for a reason: the particles carrying the current (usually, but not always electrons) scatter incoherently and inelastically from features of the conductor. In the case of an electron current, at low temperature this scattering is caused by impurities in the conductor; at high temperatures, the dominant source of ...
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Ohm's law is generally NOT correct, it's called a law for historical reasons only!! It's a law in the same sense in which Hooke's law is a law... it holds only for certain systems under certain conditions, but it's widely known because it's simple and linear!
It's not just superconductors, diodes are a neat everyday example of Ohm's law failing to hold. But ...
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