# Questions tagged [poynting-vector]

The directional energy flux of an electromagnetic field. In conjunction with Poynting's theorem and the continuity equation, it used to express the conservation of electromagnetic energy, and to calculate the power flow in electric and magnetic fields.

187 questions
Filter by
Sorted by
Tagged with
30 views

### Direction of the wave vector

The following paragraph from Wikipedia about phase/group velocity and direction of propagation is confusing me: "The direction in which the wave vector points must be distinguished from the &...
• 984
21 views

### Poynting vector and negative index of refraction

Why are the Poynting vector and the wavevector not pointing in the same direction in negative-index media?
1 vote
31 views

• 367
111 views

### Is it true that the Poynting theorem $P=E\times H$ is quite valid for DC circuits?

Can we assume that Poynting's vector theorem $P=E\times H$ is one of the universal laws of physics that applies to electromagnetic fields in AC and DC circuits.Is there A rigorous analysis of ... 67 views

### Fault/Technicalities with poynting theorem

When finding the force on a system of point particles $Q_{1}, Q_{2}$, we need to use the formula $$\vec{F} = Q_{1} \vec{E_{2}}$$ Where $\vec{E}_{2}$ is the field ONLY due to the charge $Q_{2}$, since ...
• 5,325
616 views

### Veritasium Electricity videos: where does the majority of energy really flow? [duplicate]

After watching Veritasium second video on electricity (references at the end), I have some doubts about where the majority of the energy flow actually happens. The reference experiment is the simple ...
• 152
37 views

### Where is the $\mu_0$ in this Jackson equation?

In Jackson's Electrodynamics, he derives a spherical harmonic expansion for the electromagnetic field in the radiation zone: \begin{align} \mathbf{B} &\rightarrow\frac{\mathrm{e}^{\mathrm{i( k ...
• 918
141 views

### Charged particle in crossed electric and magnetic fields

Suppose a particle with charge, mass $q, m$ respectively is initially at rest and placed in a uniform crossed electromagnetic field as shown in the figure The charge moves under the influence of ...
• 3,713
1 vote
98 views

### Radiation Pressure derivation

Radiation pressures mathematical expression according to Wikipedia is, $\frac{1}{\mu_0 c}\vec{E} × \vec{B}$ "Radiation pressure is the mechanical pressure(force/area) exerted upon any surface due ...
• 5,325
49 views

• 9,929
119 views

### Poynting's theorem ambiguity

So in wikipedia for the Poynting's theorem we have: $-\frac{\partial u}{\partial t}= \nabla \cdot\vec S + \vec j \cdot\vec E$ where: $-\frac{\partial u}{\partial t}$ is the rate of change of energy ...
• 984
1 vote
38 views

### General definition of a standing wave

Question "What is standing wave?" has already been asked. Intuitively we all know what it is, but how would we define such a wave in the most general way: for arbitrary geometry, dispersion, ...
• 42.5k
165 views

### Explanation of the Angular Momentum of the Electromagnetic Field [closed]

The fact that the EM field carries angular momentum is a well-accepted fact, and I've been trying to look into ways of showing it. I have two: One using Noether's Theorem, other using the Poynting ...
115 views

### Poynting vector and $E = hf$

Energy flux for an Em wave is defined by the poynting vector $(1/\mu_0) E \times B$ The energy is also proportional to $E^2$ If you take for example the simplest form of generating light, the ...
• 5,325
76 views

### Poynting vector in a simple circuit

The lower part of this image seems to show that energy (poynting vector) will go from negative terminal of the battery to the load,but what happens if the now drawn negative terminal of battery also ...
183 views

### Can current flow in a simple circuit if I enclose the battery in a faraday cage?

So suppose I have a regular circuit with a battery connected to a resistor and a lightbulb. Suppose now somehow the battery is inside a metal box (faraday cage) but the rest of the circuit is outside ...
157 views

### Noether's Theorem and Poynting Theorem

For simplicity, let's assume the Lagrangian formulation of Noether's theorem, that is, our equations of motion can be derived from the Euler-Lagrange equations, or, simply, that we can use a ...
83 views

### Shouldn’t the net Poynting vector at a resistor or incandescent light bulb be zero?

I’ve read that the Poynting vector points into an incandescent light bulb at all instants of time, whether there is direct/constant or alternating current through the wire. This means the bulb is ...
• 316
646 views

### On Poynting vector and electric circuits

Consider the following setup. The answer is $(3)$ - spoiler alert - and it's explained here, using Poynting vector. The thing is though How can the electromagnetic energy flux even reach the light ...
• 1,144
846 views

### Veritasium Electricity Follow-Ups: Insulators, Switch Location, larger gap

This question is similar to: Doesn't Veritasium's Recent Video About Circuits Violate The Speed Of Light? In what order would light bulbs in series light up when you close a long circuit?, ...
85 views

### Experiment to detect Poynting Vector Angular Momentum

At the very end of this Feynman lecture: https://www.feynmanlectures.caltech.edu/II_27.html he says that static electric and magnetic fields can store angular momentum in the field itself. In the ...
• 348
1 vote
125 views

### Intuition for energy density of electromagnetic fields

I have the following equations: $U = \frac{1}{2}(\mathbf{E}\cdot\mathbf{D} + \mathbf{B}\cdot\mathbf{H})$ and $\mathbf{S} = \mathbf{E} \times \mathbf{H}$ This is from the equation: \frac{\partial U}{\...
• 452
44 views

### Does electromagnetic wave violates conservation of energy when passing between two dielectric mediums at oblique angles, is there a derivation?

how can we prove that poynting theorem works for an Electromagnetic waves which incident at an oblique angles between two dielectric medium?
94 views

• 55
268 views

### Interpretation of Poynting Vector

Short Version How exaclty can the Poynting vector be physically interpreted for static electric and magnetic fields? I know that it describes the magnitude and direction of energy flow in EM-waves. ...
1 vote
63 views

### Poynting Vector Perpendicular to Surface

In Spherical coordinates if we have a source at the origin generating $E$ in the $\hat{r}$ direction and $H$ in the $\hat{\phi}$ direction then our Poynting Vector will be in the $\hat{\theta}$ ...
• 1,738
46 views

### How does a Poyinting vector act on a neutron?

How does a Poyinting vector act on a neutron? As I understood a photon action on a charged particle this action is purely electromagnetic where the electric component shake the particle perpendicular ...
• 1,785
1 vote
537 views

### AC power, EM waves and Poynting vector

Question: Does electric energy propagate as electromagnetic waves and if that is the case, how? This is clearly not the same as propagating EM waves by an antenna whatsoever. If that was the case we ... 99 views

### Fourier transform of the Poynting vector

One of the ways to define the instantaneous Poynting vector in the time domain is as follows: \begin{equation} \mathbf{S}(\mathbf{r}, t) = \mu_0^{-1} \big( \mathbf{E}(\mathbf{r}, t) \times \mathbf{...
• 21
137 views

### Validity of $E$ field energy density equation

As far as I'm aware, the most popular/rigorous way of deriving $E$ field energy density is starting with the potential energy of a continuous charge distribution (which itself has some flaws that I ...
• 5,325
1 vote
173 views

• 787
1 vote
89 views

### Energy carried by Electromagnetic Waves

The energy density carried by monochromatic planar Electromagnetic Waves is defined as: $u = \epsilon_0 E_0^2 cos^2(kz-\omega t + \delta)$ As this wave travels, it carries this energy along with it. ...
• 393