New answers tagged

1

It depends on the shape of the medium, but basically you could have an infinitesimal resistance, $\mathrm{d}R$, and integrate that. For example, for a uniform area wire of area $A$ and length $\ell$ in which the resistivity varied sinusoidally about some nominal value, $$\rho(x)=\rho_0(1+0.05\sin\left(\frac{5}{\ell}x\right)),$$ then $$R = ...


2

The naive reasoning which leads to the conclusion that charges $Q_1$ and $Q_2$ of two touching conducting spheres with radii $R_1$ and $R_2$ are related by the relation $Q_1 = Q_2\frac{R_1}{R_2}$ is wrong. This formula holds only when the distance between the spheres $L$ is large compared to $R1$ and $R_2$, $L\gg R_1,R_2$, and the spheres are connected by a ...


0

Electron density is a property of the material - same as the mass density. If you have a wire made out of copper, there will be more copper atoms in a thick wire than in a thin one - but the same number of electrons per atom. So unless you change the composition of your wire, the electron density (number of electrons per unit volume) stays the same.


4

As a general rule adding thermal energy doesn't cause electronic transitions. That's because typical electronic transition energies are a few electron volts or around 100kT at room temperature. In a metal the electrons aren't in discrete energy levels but instead reside in a continuous band of energy levels called the conduction band. While thermal energy ...


0

EMF $\mathcal{E}$ is defined as the work done in taking unit positive charge around a complete circuit. So to take a charge of $dq$ around a complete circuit is $\mathcal{E} dq$. $dq = Idt$ So the work done is $\mathcal{E}I dt$


3

Due to the cylindrycal shape of the lamp, pressure forces act compresing the glass. Since the compressive strength of glass is quite high, $\approx 10\,000$ bar, atmospheric pressure is not enough to break it.


-2

Its simple, electrons are on the outside of the nucleus of the atom. While protons and electrons can be transferred, they are on the inside of the nucleus and if they were transferred it would be considered a nuclear reaction.


0

An electric arc one get then there is an electric potential difference between two conducting materials and a medium between them. The medium has to have the property of a plasma. In a plasma there are positive and negative charged ions and they flow between the two conducting poles. In our case electrons from the one pole flow to the other pole. It is well ...


-2

Normal ambient temperatures are not usually an issue but from an electrostatic view but humidity is - electrostatic charge build-up problems increase at low humidities, especially < 30%rh. There is a link between temperature and humidity in that for a given air misture content, humidity approximately halves for a 10 degree rise in temperature. This is why ...


5

Static discharge has a strong correlation with humidity. In winter, due to low temperature, the dew point is lowered and as a result, the water content in the atmosphere is lowered. In summer, correspondingly the dew point is higher and water doesn't condense as easily and so there is a lot more content of water in the air. Now the moist air being weakly ...


0

I would focus on the current in the middle ($I_S$). When the circuit is open $I_S=0$ $$I_A=I_B=\frac{V_A}{R_A+R_B}+\frac{V_B}{R_A+R_B}=\frac{V_A+V_B}{R_A+R_B}$$ When it is closed you have $I=(V/R)_A-(V/R)_B$ and this current either adds or subtracts from the current across the bulbs. If $(V/R)_A$ is greater than $(V/R)_B$ then you will get $$ ...


1

It just depends on the nature of the substance, or rather the valence electrons. If an object has less than 4 valence electrons then it will loose electrons, and become positively charged, just to complete the octet . If it has more than 4 valence electrons it will gain electrons and become negatively charged to complete the octet. These are just ...


0

1.) When you first close a circuit, there is a very brief period of time in which the electrons push each other forward "one by one", so to speak. This very brief period of time is probably on the order of nanoseconds, so we usually ignore it. After that, a steady state condition is established, and the electrons move all at once ... more or less. Don't ...


2

You've asked some really good questions here. Before starting, I want to first mention that the traditional picture of particles moving through a wire in electostatics is missing some physics; for instance, it ignores the quantum mechanical nature of electrons. The reason we still teach this model is because it captures the main effects (the phenomenon of ...


2

In electrostatics, we generally assume our conductors to be ideal. This indirectly assumes that charges have free mobility inside the conductor. You must remember that a system is more stable the lower its energy is. A system of free charges always tries to assume a configuration in which its potential is the lowest. (This configuration is achieved because ...


0

Sign conventions aren't "wrong", but they can be misleading. For example, we could re-define work done in a gravitational field so that escaping earth's gravity well would require negative work. That's an equally valid convention, but we associate positive work with effort, so reversing the convention would hinder our physical intuition for no discernible ...


1

The electron moving from negative to positive terminal has to suffer lot of collisions with other electrons and has to also interact with the kernels present.Hence greater the length,, greater is resistance.


0

The electrons in circuits moving as a incomprehensible fluid. At least for sufficiently small electric field. So, the information of boundary on the circuit are transmitted through the electrons via equilibrium. You can imagine a lot of boxes distributed over the conductor that the circuit is made up. Each box has your own chemical potential. The information ...


1

Keep in mind that for whatever magical reason electrons repel each other (like charges), and are very attracted to protons (opposite charges). Due to the omni-directional bonding present with metals (electron sea model) electrons move freely around but the metal maintains a net charge of zero. Try not to think of the electrons as "testing the water." I find ...


0

Current is the motion of charged particles, not necessarily electrons and not necessarily in a conductor. For instance the motion of ions in a solution creates current, or holes in a solid. Currents and charges are the sources of Maxwell's equations. These sources create the electric and magnetic fields. When the sources behave in certain ways (like ...


1

Current is defined by the movement of charges from one point to another, and the concept is independent of a medium, or the charges being electrons. In this context the current is constituted by the uniformly moving charge. And that is why an uniformly moving charge doesn't create any radiation, as what happens to be a current in one frame is stationary ...


2

The second equation is essentially a special case of Gauss's law and could refer to a variety of situations. The first equation happens to be a special case of the second equation. Gauss's Law says the total of the electric flux out of a closed surface is equal to the charge enclosed by the surface, divided by the electric permittivity ($\epsilon_\circ$). ...


1

The first one is the force between two point charges and the second one is the electric field between two uniformly charged plates. Now you edited your post, so the first one is the electric field of a point charge $q$.


1

It basically conducts electricity the same way salty water does: both contain some concentration of charged particles that are free to move. Water contains some concentrations of ions and protons (H$^+$ protons). When there is a voltage difference, the ions will move according to their charge. The hot gas of the flame contains positively charged ions and ...


1

Although there are many free ions and electrons, I strongly doubt that it would be sufficient. Consider this: electrons always take the path of least resistance. If the atmosphere was that conductive, then the battery would just short out because the electrons would just go from pole to pole of the battery without going through the bulb.


0

first of all when electrons are moving they are really similar to Newton's Cradle.the back electron pushes the front one. different in electric potential of terminals do work on electrons and causes circuit.now moving electrons as you said collide atoms which increases temperature. in fact potential electric energy turns to kinetic energy and kinetic energy ...


0

I calculated it.As you may know it is because of different resistance that building and conductor have. what your teacher said is true but not effective really.


0

According to the concept of drift velocity, on the average no. of electrons travelling in any direction will be equal to no. of electrons travelling in the opposite direction. As the electron accelerate, they frequently collide with positive metal ions or other electrons of metal.Between 2 successive collisions an electron gains a velocity component(in ...


0

Energy is carried as Kinetic energy by electrons from which useful KE comes from Electric Field. Electrons are under acceleration due to Electric Field in wire. When millions of accelerating electrons collide with other ellectons they increase average KE of electrons which increase temperature of wire. Electrons entering wire leave wire equally, without any ...


1

in this scenario, no electrons should be leaking from the circuit; and the number of electrons that enter the circuit (-) should be equal the the number of electrons that exit the circuit (+), am I correct? Energy conservation is not the same as charge conservation. The energy that electrons carry is determined by the circuit, an average drift velocity, ...


1

Each material has some internal resistance, so moving electrons collide with other electrons and release energy in form of heat. Read more


0

The way you conclude that there's no field inside a conductor in equilibrium is this: there are no currents in equilibrium, therefore (by Ohm's law) the electric field is null. Out of equilibrium and in the presence of currents, Ohm's law says you get electric fields. If you want to look into microscopic explanations of Ohm's law, check out the Drude Model. ...


0

In your case there will be a negative potential on the conductor and the potential on earth is zero. When you ground it there will be a potential difference, so the electrons will move until the potential difference becomes zero ,i.e. electron will move to ground. Then finally the potential on the conductor will also be zero. Since, a neutral metal ball ...


0

First there will be a potential on the conductor and the potential on earth is zero. when we ground it there will be a potential difference, so the electrons will move until the potential difference becomes zero. Then finally the potential on the conductor will also be zero.


2

The Key to your question is the distinguation between ideal and real sources of voltage and current. If we stay at the batteries: At the moment you attach batteries paralell to your body, what happens is that one part of the body has another electric potential than the other one, thus (Ohms law) a current will flow in your body. At this point the current ...


2

The powerline can supply large amount of current, whereas the doorknob cannot. Each power supply comes with voltage and max rated current. Let us say body resistance is 5M ohm. Then current flowing through the body when you touch powerline is 20k/5M = 4mA. Now powerline can easily supply 4mA of current. But the doorknob cannot supply 4mA. So the actual ...


0

The live wire oscillates and either drains or supplies electricity to the neutral wire. The live wire oscillates between 230V to -230V and the neutral wire always stays 0V.


1

You can confine an electric field in a Faraday cage, if you want to, then the volume is finite. – CuriousOne


2

Most utility-scale (large-scale, the thing you've referred to as "government") generation is photovoltaic. Photovoltaics work on any scale, from watts to gigawatts. Whereas concentrating solar thermal generation needs to get a mass of fluid up to hundreds of degrees celsius, in order to drive a turbine. It's absurdly inefficient (in energy terms and ...


2

The current in a circuit is a collective phenomenon from zillions of electrons. It appears due to conductivity, another collective phenomenon . It is a cumulative behavior of atoms and electrons in matter. In insulators, electrons occupy energy levels and have to be actively kicked out of them, with the energy provided by an interaction. Insulators can be ...


0

If you put the two poles of the electric source close together and put a carbon filament between them, perhaps you will see a plasma arc. The carbon has gone, but for a powerful enough source the flow of electrons does not stops (until the source is not exhausted). The potential difference (the voltage) is responsible for the velocity of the flowing ...


1

You seem to be asking, "what happens to an electron when its voltage changes?" In short, nothing happens. An electron has no idea what voltage it's at. You claim this is different from an object's height, but it's actually exactly the same. If you only look at an object, by itself, you'll have no idea what height it's at. Nothing about the object changes ...


0

Ok, that's a bit tricky: These books propably use the assumption that the wire is a perfect conductor. What follows is that any difference in the electric potential $\Phi$ allong the potential will create a field (as you said). BUT, and here is the clue: Since it is a perfect conductor, and electrons have little mass compared to the force that the electric ...


2

There are two aspects to your question. One is: "when I run across an artificial turf field with plastic soles, why do I accumulate static charge?" and the second is "When I am charged, why do I experience a shock when I touch a metal goal?". Taking each in turn: There is a phenomenon called triboelectricity - the generating of a potential difference when ...


0

When a conductor is placed there would kind of same phenomenon. The electrons will develop on the side of positive plate. But here unlike dielectric there will be complete accumulation of charges on the surface. Hence there will be complete cancellation of Electric field inside the conductor. Hence the force will decrease more.


2

The magnet may decelerate "at the last minute" if it's sufficiently strong. The difference with the first setup (dropping in a tube) is that the change in flux (and therefore induced currents) in the copper plates is small until the magnet gets very close - the field of a dipole goes with $\frac{1}{r^3}$. By contrast, as you are falling down a tube, there ...


1

A resistor is not a free electron metallic structure but a complex metallic chemical composition. Some electrons in a drift field will actually pass through the complete lattice. This becomes the resultant drift field current through the system. Others will collide with the outer shells of the molecules of the complex material and cause them to jump and ...



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