# Tag Info

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If you have a metal of some resistivity, it needs an electric field inside of it to sustain a current. If there is an electric field in it, the line integral $\vec{E}\cdot d\vec{\ell}$ (which is the electromotive force) along a segment is nonzero. Hence there's a voltage somewhere. If there weren't, there could be no current. Likewise, one of Maxwell's ...

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In an inductor you are also using the voltage, and hence current flow, to "pump up" the magnetic field and when the voltage is removed or reversed the field collapses generating a reverse voltage and current.

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This is a really good question. I have also thought about this quite a bit. At present, it does not seem like it is possible with a standard experimental probe. Inelastic x-ray scattering and electron energy loss spectroscopy only measure the longitudinal response function at finite frequency and momentum. As you said though, if you are only seeking small ...

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Current is not exactly a flow of electrons but rather a flow of charge. Electrons carry charge, so it is related and you might hear it like that here and there. But remember that not only electrons can carry charge, other types of particles can do that to. We still call it current in those cases, because current is just charge per second moving through. ...

1

When you first connect the source, there is a very brief transient during which the steady-state DC solution is set up. The speed of the signal, i.e. the electromagnetic wave front that carries the information along the wire, is a bit less than the speed of light because of transmission line effects. Figuring out exactly how long the transient lasts would ...

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Dissolving salt in the water creates sodium and chloride ions which in the presence of the potential of the battery provide a path for current flow, the movement of charge. Thus resistance is decreased and current is increased. While an ideal voltage source would see no decrease in the voltage, a real world battery has its own internal resistance, and so ...

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Notice, the magnetic magnetic field $B$ at the center of a coil carrying current $i$, with radius $r$ & having $n$ no. of turns $$B=\frac{\mu_0}{2}\frac{ni}{r}$$ hence, magnetic flux $\phi$ linked to the coil is given as $$\Phi=BA=\frac{\mu_0}{2}\frac{ni}{r}\pi r^2=\frac{\mu_0 \pi nir}{2}$$ now, setting the value of $\phi$, we get ...

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is [AC current] slower than DC current Current doesn't have a speed, it is a measure of charge passing per unit time. Current can be larger or smaller but not faster or slower. If we know the Mississippi river flows at a rate of 17000 $m^3s^{-1}$, we don't know how fast the water is moving (and for many purposes may not care). If AC current ...

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Yes it does. Classically, the current density in a conductor is given by $\vec j = e \vec v_D \cdot n$, where $n$ is the concentration of charge carriers, $e$ is the charge of the charge carriers and $\vec v_D$ is the drift velocity (this is part of the Drude theory). The drift velocity is the average velocity of the charge carriers, the idea is, that they ...

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No, a steady-state current is not constant throughout space, it is only constant in time. You are correct that $\vec\nabla\cdot \vec J = 0$ implies $\partial_t\rho = 0$ by the continuity equation, but that the charge inside arbitrary volumes doesn't change doesn't mean something about the current "behind & in-front" of the volume. It means the same ...

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I'm sure you are familiar with current defined on a line or on a plane or in a volume. Similarly, a point current would involve a dirac delta function. The current is $$I = q\mathbf{v}\delta (\mathbf{x} - \mathbf{x'})$$ $\mathbf{x'}$ is the position of the particle and $\mathbf{x}$ is an arbitrary point in 3 dimensional space . $\mathbf{x'}$ is a function ...

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Specially if length of the wire was large, say 3 * 10^8 meters, then would the movement of electrons on one end of the wire be "in sync" with movement of electrons on the other end? No, they wouldn't and this fact is crucial for understanding antenna operation. Note that even short conductors become electrically long if the frequency is high ...

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As the other answers point out, there are a vast number of electrons in a piece of wire, and no single electron must traverse the whole circuit for a current to flow. You can think of an ac current as more of a sea of electrons sloshing back and forth. I'll focus on your second question: How would the electron flow in DC circuits work if a bulb and a ...

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Because of electromagnetic forces, all of the electrons in the wire are displaced towards A with a certain velocity causing a positive current towards B. The electrons have a small drift velocity, not moving much. Although your light turns on very quickly when you flip the switch, and you find it impossible to flip off the light and get in bed ...

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Think of AC as something that starts out as a positive DC voltage. Then it starts going in the opposite direction. Then back again. And continues doing that over and over. Then smooth the current change out and make it sinusoidal. Now you have AC.

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It is due to the electric field that is set up that will cause the electrons to move. The drift velocity of the electrons is much slower. There will be a delay in switching on the bulb, and it is equal to approximately $l/c$, $l$ being the length of the wire. Your diagram is not exactly right, as it shows as if the electrons are being produced at one end and ...

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Are you asking why the electrons in wires exhibit this behavior? If so it is due to the fact the path of moving electrons is curved when in a magnetic field and how much it curves increases when the magnetic field increases. Since the electrons in wires are always moving about randomly and never still, their paths' get curved. This net rotation of electrons ...

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"Current takes the path of least resistance" is just a phrase people say but it's not totally accurate. When one path through the circuit has 0 resistance (a short), it is true that current follows that path only. It isn't true when you have multiple paths, with nonzero resistance, though. A better way of saying it would be "current flows through all paths ...

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$V = iR$ but $P = iR^2$, so if the current, $i$, stays constant but if the resistance, $R$, increases, then the power, $P$, increases too.

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If you are comparing two voltages with identical currents, you cannot be talking about the same bulb in both cases. This means that you are comparing two different bulbs, and there is no way to tell which will be brighter, since different bulbs can be designed for different luminous efficacy, which is light per unit power. For instance, a bulb can be ...

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If you write the current as a function of time, $I(t)$, then the root mean square current is: $$I_\text{RMS}^2 = \frac{1}{\tau}\int_0^\tau I^2(t)dt$$ where $\tau$ is the period of the waveform. In this case $I$ is always $\pm 2$ so $I^2$ is always $4$ and the integral becomes: $$I_\text{RMS}^2 = \frac{1}{\tau}\int_0^\tau 4dt = \frac{1}{\tau} 4\tau = 4 ... 0 Q1. "from the above values we can calculate Power(P) as P=V∗I" A1. Yes. Power=10W Q2. "If voltage is amplified or raised to 4 times that makes V value to 20 V, what happens to the values of current and power." A2. Assuming your load is a resistor, then your original load resistance was 5V/2A=2.5Ω. Therefore, if you increased the voltage to 20V, your ... 1 A resistor is defined as the circuit element for which the voltage across is proportional to the current through and the constant of proportionality is the resistance R:$$V_R = R\cdot I_R $$Clearly, for this linear relationship, it is also true that$$\frac{dV_R}{dI_R} = R$$However, for general circuit elements, the derivative of V(I) is not a ... 2 R(V,I) = \frac{V}{I} by definition, it is not a gradient. r = \frac{dV}{dI} is called the fractional, differential, dynamical or small-signal resistance. It just happens that for resistors R(V,I) = R_0 is a constant, thus the two quantities are the same: r = R_0. 1 Why and how does a resistor limit the current flowing through the entire circuit? doesn't it limit only the current that is flowing past and after the resistor? First, this is a DC circuit (ignoring the switch) which is to say that the circuit voltages and currents are constant with time. Since that is the case, by conservation of electric charge, ... 1 Two questions: How can the ammeter tell how much current is flowing the resistor? since it's "behind" the resistor? There at least several means that current can be measured using different technologies. The early ammeters used galvanometric technology where a coil in the galvanometer becomes part of the current path. The coil generates a magnetic ... 0 The term current is actually improper term. The electricity has two components to put it in simple terms. Current and Voltage. The supply that we get in our homes in AC supply as to the old system of Dc supply. The AC supply of the poly phase alternating current system invented by Nicola Tesla is the modern ac supply. The current never gets less as it ... 0 There are lot of phenomenons in electric current, that lead to loss of energy. 1) An alternating current (AC) works the way that electrons in the wire get accelerated forth and back 50 times per second (50 Hz in Europe, 60 Hz in other regions). Any electron acceleration is accompanied by the induction of a magnetic field. This magnetic field led to some ... 1 Current loses energy through collisions of its carriers which are electrons. Electrons in a wire move in a definite direction and this motion in a definite direction is what we call current. But there is one missconception in your question. Current does not travel from a station to our home. In stead, all the electrons that are just siting there in your ... 0 Not an expert in this but I can try to answer some parts of your question. As you pointed out, one can find the optical conductivity to measure the current-current correlation. For that if you use linear response then you can conclude the following (for an isotropic material):$$\sigma^{ij} = \sigma_L \frac{q^i q^j}{q^2} + \sigma_T \left( \delta^{ij} - ...

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The force on a current carrying wire is given by: $$d\vec F= I d \vec l \times \vec B$$ Or for a uniform current and field and in scalar form: $$F=BIl$$ If you want to derive this from $$F=qvB$$ then you can note that in a time $t$ a total charge of $\frac{q}{L} vt$ passes through a point in your conductor. Since current is charge per unit time we have: ...

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Perhaps this is what you are looking for: Screen capture: http://www.falstad.com/circuit/ The default circuit, as shown, is an LRC circuit. On the Schematic: Gray is 0V Green is Positive Voltage Red is Negative Voltage The yellow dots are a visualization of current: positive holes. The graphs along the bottom, from left to right, are for the ...

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Use the right hand rule. Point your thumb in the direction of the current and your fingers will curl around the wire in the direction of the magnetic field. For current flowing from a to b: Your thumb points down and to the right. Your fingers will be to the left of the loop pointing downward. If you curl them around you will see that the magnetic field ...

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You can get the direction of the field without actually drawing it. The magnetic field of the current through the resistor is not just up or down. The field lines go in a circle around the resistor. You can use the right-hand rule to visualize which the way the lines go around, either clockwise or counterclockwise. If the current flows from $b$ to $a$, ...

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I think you're just asking for some clarification on terminology. Imagine a circuit which consists of only a resistor (passive component) connected across a battery (an active component). The end of the resistor connected to the battery's positive terminal will be it's positive end. In the conventional current model, current flows out of the battery's ...

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Note: $c=1$ in the following. Every time-like worldline can be parametrized by its proper time. If you are given $\vec r(t)$, then the proper time at $t_0$ is given by $$\tau(t_0) = \int_0^{t}\sqrt{1-\left(\frac{\mathrm{d}\vec r}{\mathrm{d}t}\right)^2}\mathrm{d}t$$ and inverting this expression to get $t(\tau)$ gives you the worldline \$r^\mu = ...

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as a thought $$\nabla \times j = M$$ $$\nabla \times M = j$$ this current density has three manifestations shown in amperes material derviation: $$\nabla \times B = \mu_0(j_f + j_p + j_m) + \epsilon_0 \frac{\partial E}{\partial t}$$ Current due to change in polarisation $$j_p = \frac{\partial P}{\partial t}$$ Current due to rotation of magnetisation ...

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