# Tag Info

12

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 ...

10

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 ...

5

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 ...

3

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 ...

2

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: $$I_\text{RMS}^2 = \frac{1}{\tau}\int_0^\tau 4dt = \frac{1}{\tau} 4\tau = 4 ... 2 R(V,I) = \frac{V}{I} by definition, it is not a gradient. r = \frac{dV}{dI} is called the fractional, differential, dynamical or small-signal resistance. It just happens that for resistors R(V,I) = R_0 is a constant, thus the two quantities are the same: r = R_0. 2 Notice, the magnetic magnetic field B at the center of a coil carrying current i, with radius r & having n no. of turns$$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}$$now, setting the value of \phi, we get ... 1 When you first connect the source, there is a very brief transient during which the steady-state DC solution is set up. The speed of the signal, i.e. the electromagnetic wave front that carries the information along the wire, is a bit less than the speed of light because of transmission line effects. Figuring out exactly how long the transient lasts would ... 1 A resistor is defined as the circuit element for which the voltage across is proportional to the current through and the constant of proportionality is the resistance R:$$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 ...

1

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 ...

1

"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 ...

1

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 ...

1

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.

1

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 ...

1

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 ...

1

When the system reaches steady-state condition(things do not change with respect to time), then we have the same electric field inside the circuit. Before reaching the steady-state condition, then yes, the forces exerted on the electrons(or voltage difference between some points) is not the same at every point in the circuit. But, as Griffiths puts it in his ...

1

Because no charge is accumulated at any point anywhere when you have a steady current! If water is flowing in a pipe, you maybe have 1 cubic meter passing every second. Every part of the pipe system MUST get $1\;\mathrm{m^3}$ in every second and MUST also send $1\;\mathrm{m^3}$ out every second. If not - if for example more enters than what leaves every ...

1

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 $a$, ...

1

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 ...

1

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 ...

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 ...

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 ...

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, ...

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