# Tag Info

## New answers tagged electricity

1

In my understanding the major problem with solar flares are the (near) DC currents that get induced in power lines (phone lines have DC blocks, so that's not a problem). Since both ends of a power transmission line are terminated by a transformer, the DC current will induce a DC magnetization in the transformer cores. Since the transformers are run close to ...

4

If the flare drops energy into the atmosphere, it sets up a changing electric field. The strength of the electric field is measured in $V/m$. This means that the longer the distance, the greater the potential difference. If you have a short wire, the potential between one end and another is not very large. But a long wire can connect points with much ...

0

If the state of the atoms around it are solid, then it is because the atoms are stuck together.

1

since there is no resistance. That's not quite correct; in fact, there is infinite parallel resistance or, better, zero parallel conductance. Recall that, for a parallel RLC circuit, the circuit elements are parallel connected. If the parallel resistance were zero, the Q would be zero since the resistance is effectively an ideal wire shunt across the ...

0

One way of thinking about a $Q$ factor is as a measure of how many periods of oscillation it takes for the amplitude to dissipate (for concreteness, lets say the number of periods required for the amplitude to decrease by a factor of 2). Then an LC circuit (that is, a series RLC circuit with $R=0$) has no dissipation and therefore will undergo infinitely ...

10

The answer is that electrical excitation of air molecules is able to produce lots of excited singly ionised nitrogen ions. The electronic structure of singly ionised nitrogen has a number of allowed radiative transitions, where the outer excited valence electrons can rearrange themselves into lower energy configurations. The most prominent turn out to be ...

1

Let's say you want to know the electric potential difference r meters away from an electron sitting in a void of space. We will denote this potential difference as $V_e$. The electric potential difference describes the difference in potential energy of a unit positive charge from one point in space to another and the work done on a unit positive charge to ...

27

The deexcitation of nitrogen and oxygen, the primary components of air, are that of blue/purple. See http://en.wikipedia.org/wiki/Ionized-air_glow for pictures of nitrogen and oxygen in gas discharge tubes.

42

Air is normally a bad conductor of electricity, but with enough voltage it can be converted to plasma, which is a good conductor. In a plasma, the electrons constantly bind to and leave atoms. Each time an electron binds to an atom, it emits the energy in light. As a result, the plasma glows the color of a photon with that energy. There are a few different ...

1

Take a look at the Drude model. It gives a fairly intuitive way to look at conductivity in solids. Although later proved to be slightly incorrect due to the ignorance of quantum effects, it does the job for a classical explanation. One can reason as to how heat is generated in the conducter in a classical manner from the Drude model. As the electrons move ...

-4

AC is a form of oscillating power, like a jig saw. The generator uses magnetic induction which, as you know has two poles + and - . One hertz, or one rotation creates one complete cycle but one cycle is comprised of both + and - forces. Also one cycle is considered a sine wave, or sinusoidal wave. A phase is considered a separate sine wave. If you live ...

7

A light bulb wouldn't turn off, because no matter what direction the electricity is flowing through it, it is still electricity. It doesn't gain some anti-electricity effect. Here is an analogy with water. The water works flowing forwards and backwards. (Although in this example there is a stop.) If there is still confusion, however, remember that ...

0

It can be done. Just spray electrons on an insulator, they will stick. This is for example used with paint drops for painting metals. The paint drops are charged by corona ionizing the air near the nozzle and the piece of metal to be painted is charged, this way less paint is lost (as the paint drops are attracted to the piece of metal). Furthermore, at ...

0

Are they insulators? They do not conduct charges very well by definition, and thus one should choose another approach instead of trying the 'conduction' way.

2

Actually, we don't know that "filament bulb has straight Volatage vs Current graph": "The actual resistance of the filament is temperature dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold ...

2

Since I understand that power = V x Current, the power for a bulb can not be a constant if its resistant is assumed a constant. A normal mathematical thinking can confirm that. If the voltage and current don't change, then the power is constant. The electricity supplied from the wall is at 115V (more or less). If the resistance of the bulb is 1322 ohms, ...

2

The power rating given on lightbulbs always refers to the power at a specified operational voltage (which is always given together with the power or implied by the type of socket). The power at different voltages is not easily predictable as the resistance of the filament will vary strongly in dependence of temperature (which depends on the dissipated ...

1

You are right in stating that potential and hence potential differences are dependent on field. The relation in fact is $\mathbf{E} = -\nabla V$ Hence, as we can see, if $E$ = 0, then $\nabla V$ is in fact constant, not $V$. Now, to compute the potential, we can rely on coloumb's formula, taking $V$ at infinity t be zero, for a differential ...

1

Definition of potential difference is the amount of work per unit charge to move a charged particle from one place to the another place. The potential difference between point $a$ and point $b$ is as below, $$V_a - V_b = - \int_{\mathbf{r}_b}^{\mathbf{r}_a} \mathbf{E}\cdot \mathrm{d}\mathbf{r}.$$ What we call as potential with $V=\frac{kQ}{r}$ is the amount ...

1

I think the electric field is zero on A, B, C, D and E, because otherwise there would be current, which would be odd And you are totally right for an electrostatic system (with no current). Instead of explaining it by, "this would be odd", let's have a look at what happens in the instant you add the wire to the battery pole.: Before the wire touches ...

1

Because observations made by physicists have found that this is what nature does.

1

The rest of the energy is basically emitted as heat energy. Why? You have two capacitors in the circuit, and the connecting wires offer negligible resistance. Hence, when electrons flow from the charged capacitor to the uncharged one, the electrons basically face no resistance, and they collide with high speed with the uncharged capacitor. This collision ...

0

There are many different levels of explanation for this question. Strangely enough most of them will dive into quantum electrodynamics, Feynman diagrams and exchange of virtual photons... I will try a simpler path that still carries some explanation. When you put two charges at a distance, they deform the -- otherwise flat -- electromagnetic (EM) potential ...

1

you can draw feynman digrams and then calculate scattering amplitudes and it is in the non relativistic limit is proportinal to potential.so if the potential is positive it means they repel. this sort of claculation is done in peskin book and A.Zee book.in peskin book page no 125. this is the most rigorous work to prove gravity is always attractive. by ...

1

(Other) Rob's answer seems good to me, but let me offer another way of thinking. As you approach the surface of the sphere very closely, the electric field should resemble more and more the electric field from an infinite plane of charge. If you check Gauss's law (recalling that the field in the conductor is zero) you will see that if the surface charge ...

1

Firstly, I would like to say that there is no particular terminal separation between negative charges and positive charges. Actually you will understand it better if I would clarify in this way that scientists first saw that having even follow the same statistical distribution i.e. Fermi Dirac distribution some of them actually repel others and some do ...

1

You seem to be confused about the concept of the limit, which is normally covered in calculus courses. If you have, not a point charge, but a volume of charge with some density $\rho$, then the charge enclosed in a small sphere with radius $r$ is $$dq = \rho\, dV = \rho \cdot \frac{4\pi}3 r^3$$ and the electric field at the surface of the sphere will be ...

0

I know this is a little more than you asked for, but lightning is very interesting. A lightning event is usually called a flash and lasts about 0.5 seconds. It consists of a near-invisible stepped leader followed by a very bright return stroke backwards along the path of the stepped leader. Following the first stroke, there may be additional strokes in the ...

0

While Gauss' law does imply that the electric field terminates only on charges, it certainly does not imply that it cannot form closed paths. Gauss' law may be expressed as follows: $$\nabla\cdot\mathbf{E} = \frac{\rho}{\epsilon_0}$$ From the Helmholtz theorem of vector calculus, as any vector can be expressed in terms of two parts ($\phi$ and $\mathbf{A}$ ...

0

Gauss law states that electric flux through a closed surface equals $\frac{q}{\epsilon_0}$, where $\epsilon_0$ is a constant and $q$ is the charge contained in the surface. So, if we corner a 'point charge' using a spherical closed surface, with the charge at the center of the sphere, all we have to do is to start reducing the radius of the sphere. Because ...

2

Can we have electronics with charge carriers OTHER than electrons? Yes, see what Sebastian said above. And see the physicsworld article Taming light at the nanoscale: "Look around, and you will probably see numerous electronic and optical gadgets, such as mobile phones, personal digital assistants, laptops, TVs and digital cameras. These may all do ...

4

Depending on your view, there is electronics with other charge carriers. It is commonplace to have semiconductor devices where the relevant carriers are holes! Furthermore, batteries and electrolysis relies heavily on ions as charge carriers (but hardly count as electronics). I guess genuine electronics with ions will be difficult as charge carrier mobility ...

0

You need something that can be conducted along the wire to power electronics; if you were to get protons, rather than spreading from atom to atom you'd just end up changing the element of the atom or splitting it. The closest thing that you can do other than add electrons is chemically charge it, as in replace the batteries.

0

On AC a nice measure to take could be the effective current. Its definition is the following: The effective AC current is the current value such that the average power transfer would be the same on an DC current. So, power is therefore calculated: $$P(t) = V(t)I(t)$$ For AC circuits where voltage and intensity varies with time, we have a varying power: ...

0

In a circuit, an electric field is created. This electric field forces electrons to move. As current must remain constant (since no charge build up is observed), the electric field must be strongest in the materials that are the least conductive (or most resistive). As this electric field moves the electrons, they gain kinetic energy. In order to conserve ...

0

I will try to explain with some examples. There is never a potential difference when there is equilibrium. You can think of it as a height difference. Think of positive potential as a high point and the negative one as a low point or ground. So there is a height difference. A thing at the high point is bound to come down. Similarly, whenever there is ...

2

The boundary conditions you mention, $$\vec{D} = \rho_s\hat{a}_z$$ are for charges distributed on the surface of a volume conductor, following from the requirement that the electric field is zero inside the conductor. The expression $$\vec{E} = \frac{\rho_s}{2\epsilon}\hat{a}_z$$ is instead valid for a planar sheet of a conductor alone (or for that matter, ...

2

It is really a matter of combinations. Potential energy is a feature of a system, so between two particles there is one potential energy. The summation however, will cadd the potential energy between two particles twice (e.g., $q_1\phi(\mathbf{r}_2)$ and $q_2\phi(\mathbf{r}_1)$). Hence, the one half term has to be introduced so that the potential energy of ...

0

As explained here, "Electric current is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes." The charge in a normal conductor is essentially all due to electron flow. Therefore, the rate of electrons past a given point in a circuit (your computer) can be calculated based only on the amount ...

0

You are correct that the resistance in some materials will increase as the temperature increases, and that the temperature can increase as a result of current flow. It still obeys Ohm's Law, however, as the relationship that Ohm's Law describes still holds. In other words, as the resistance increases, the current will decrease, just as Ohm's Law says it ...

0

The reason for restricting temperature change is that some materials exhibit a change in resistity when the temperature changes. If the resistivity is constant versus temperature the resistance won't change. In that case, there is no need to restrict the temperature. A resistor is ohmic if it exhibits a constant slope V vs I curve. That resistor obeys ...

0

To answer the first question, consider that if the electric field acts in one dimension, then $\mathbf{E} = -\frac{d\mathbf{V}}{dx}$ Hence, in a uniform field the potential changes linearly across the direction parallel to the field. Like this image, where the potential increases by a constant amount at each equipotential as we go left (because field ...

10

The point of the point is to increase the electric field near the point. Small radius curves will have a higher local electric field, eventually creating a localize area where the field is greater than the dielectric strength of the air. This results in what I refer to as "micro-lightning." This microlightning discharges the air (or cloud) before the ...

9

Suppose that you have an negatively charged cloud. Floating over your conductor. Then making your lightning conductor pointy at the edge, facilitates better discharge. Because the electric field set up would be high. ${\sigma}=\frac{q}{4\pi r^2}$, We will take an spherical approximation of the pointed end. It will have a very small radius thus high surface ...

1

The potential difference between the two points on the wire is negligible at all times but initially there's a potential difference between the wire and the bird and there would be a (very short lived) transient current which is similar to electrostatic discharge you feel when you touch an object with electrostatic charge build-up.

-1

You might be asking how metal is such an efficient conductor. Some of the electrons move freely as a fluid. They are not locked in place around the atoms, and don't need "room" in the classical sense. Here is a wikipedia page going over the real details. On a scale much larger than the inter atomic distance a solid can be viewed as an aggregate of a ...

33

The electrons themselves don't move all that fast. The wave energy is the part that moves quickly. Picture it this way. You have 500 meters of pipe, with a small hole at the other end. The pipe is full of water and you increase the pressure at your end. Water will flow out the other end immediately. This is the electrical energy (pressure) and the ...

-1

Electrons can sneak pass all the atoms because of their wave function. They behave like waves not like particles. In short, because of quantum mechanics. In a periodic assembly of atoms like metallic solid they should not feel any resistance when moving through but because it is not perfectly periodic they feel aperiodic potential and this is why they ...

14

In fact, electron's speed is not so fast that light bulb glows up immediately. It is the electromagnetic field which travels in the circuit at near the speed of light that is resposible for it. After turn on the light, electron only acquires a little speed in addition its thermal speed. The thermal speed of electron can be estimated by \$mv^2/2\approx ...

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