# What is Electromagnetic energy: Definition and 30 Discussions

In physics, and in particular as measured by radiometry, radiant energy is the energy of electromagnetic and gravitational radiation. As energy, its SI unit is the joule (J). The quantity of radiant energy may be calculated by integrating radiant flux (or power) with respect to time. The symbol Qe is often used throughout literature to denote radiant energy ("e" for "energetic", to avoid confusion with photometric quantities). In branches of physics other than radiometry, electromagnetic energy is referred to using E or W. The term is used particularly when electromagnetic radiation is emitted by a source into the surrounding environment. This radiation may be visible or invisible to the human eye.

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1. ### I Neil deGrasse Tyson on Nikola Tesla and electromagnetic energy

I came across this video where Dr. Tyson talks about Nikola Tesla. Neil Tyson on Tesla. From 4:47 onwards, he says "We now send energy through wires", and talks about how bizarre it would be to walk around/stand in the way of such energy flow. Further he says the power transmission lines are...
2. ### I Sachs-Wolfe effect in a Dark Energy universe?

The integrated Sachs-Wolfe effect occurs when a photon goes through a gravitational potential that changes due to spacetime expansion (presumably caused by dark energy). For that reason, a photon going through a gravitational well would gain energy (blueshift) when entering and it would lose...

4. ### Calculate the power measured by the detector at distance h from the source

Homework Statement An isotropic point source radiates electromagnetic energy, and its output is measured by a thin disc-like detector of radius R. Calculate the power measured by the detector at distance h from the source, assuming that the plane of the disc is orthogonal to the line of sight...
5. ### Can capacitors receive EM energy?

Dynamos and transformers have inductor coils reacting with changing magnetic fields and importing energy into the circuit in form of induced current 1. What about the counterpart of above principle in case of capacitors? 2. Will capacitors interact with...
6. ### I Poynting energy flow in Eath's atmosphere?

1.There is an electric field between ionosphere and ground, also Earth's magnetic field is perpendicular to this E field, hence by poynting theorem integrating E x H across the entire surface of Earth gives a great deal of energy flowing west to east. 2. |S| = (E X B)/u0 = (150 V/m X...
7. ### Converting Electromagnetic Energy To Temperature

Homework Statement For a home work assignment, I have to build a theoretical device which uses a laser to boil water. But I have no idea how to figure out how long it would take the device to transfer enough heat to boil the water. The laser diode has a wavelength of 445nm. We are supposed to...
8. ### Electron Spin Problem: Exploring the Stern-Gerlach Experiment

Hello, I've been reading the Stern-Gerlach experiment, and where the concept of electron spin is introduced, am facing a problem, i.e., if you consider electron a charged rotating sphere, then the electromagnetic energy and size of the electron becomes huge! So how do you deal with this? Thanks...
9. ### Can Electromagnetic Energy Be Harvested and Converted into Electrical Energy?

Hey can I produce a electromagnetic radiation at 2.4 ghz from a 10 volt source then walk 25 meters away harvesting the electromagnetic radiation with a 2 foot copper wire turning it back in electrical energy to power a led
10. ### Raising Index of Electromagnetic Energy Momentum Tensor

The General Relativity text I am using gives two forms of the Electromagnetic Energy Momentum Tensor: {\rm{ }}\mu _0 S_{ij} = F_{ik} F_{jk} - \frac{1}{4}\delta _{ij} F_{kl} F_{kl} \\ {\rm{ }}\mu _0 S_j^i = F^{ik} F_{jk} - \frac{1}{4}\delta _{ij} F^{kl} F_{kl} \\ I don't see how these...
11. ### E=cB and electromagnetic energy density

I have to questions that I can't seem to understand. I've seen in my textbook the relation E=cB being deduced from Faradays law applied to some type of rectangular loop. The problem is this is done with regards to a planar wave. So is this relationship general for all EM waves? If so, how? And...
12. ### Bragg's law and the distribution of electromagnetic energy.

While I get the coherent and incoherent scattering process that leads to the bragg diffraction condition, I don't really understand the physical mechanism behind the transmission and reflection. Now, as I understand it, the bragg diffraction condition is satisfied only for one or two particular...
13. ### Electromagnetic energy of a long wire

When we have a current in a long wire, what is the kind of total energy of the system? We do have an electric field inside the wire and a magnetic field outside it. I think the electric field has an energy, say E, and it is only this energy which appears also as magnetic energy and we don't have...
14. ### Chemical energy to electromagnetic energy transer

Does anyone know of reaction that can generate a a steady source of light? Preferably one easier to activate than burning of magnesium strips(which is too momentary anyway, I'm trying to make a chemical reaction that can eventually power a photoresistor/ light).
15. ### Compress a very hot plasma, change in electromagnetic energy?

Say I have a volume of hydrogen gas that is raised to a temperature T so that 99.9 percent of the gas is ionized. If now, with the plasma at some pressure P, the volume is compressed a small volume dV such that no energy leaves the volume I'm curious of a total accounting of where the energy PdV...
16. ### Positive source for electromagnetic energy

We know that the conservation of electromagnetic energy is expressed via the continuity equation below: \large{\frac{\partial u}{\partial t}}+\vec{\nabla}\cdot\vec{S}=-\vec{J}\cdot\vec{E} with u=\frac{1}{2}(\vec{E}\cdot\vec{D}+\vec{B}\cdot\vec{H}) and \vec{S}=\vec{E}\times\vec{H} . It...
17. ### Electromagnetic Energy Density

Homework Statement Find the electromagnetic energy and momentum density and their ratio. \\Determine the instantaneous values of the energy density, momentum density, intensity, and stress associated with the electromagnetic fields for the following cases. Also, identify these cases. Assume...
18. ### Electromagnetic energy injected into combustion process?

Hmm, not sure if this is the right place to be asking this. I am wanting to understand what effects electromagnetic energy can have when injected into the combustion process of hydrogen and oxygen? Can anyone tell me or point me what effects can occur or point me in the right direction to...
19. ### Where Does Electromagnetic Energy Go?

Hi all physics lovers, please bear with my question as its like a kid wondering about something :) Energy can neither be created nor be destroyed. So when I switch off an electric bulb, there is darkness. So where does the electromagnetic energy go? :confused: Thank you.
20. ### Why does electromagnetic energy only pass through certain hole sizes?

I have noticed in faraday cages and in microwaves that the holes in the screen manage to prevent certain frequencies from passing through them. Why it is that this happens?
21. ### Electromagnetic Energy propagation

Hi All Is the following statement true: Electromagnetic energy requires a wave medium to propagate. (The way free electrons in a copper conductor transfer energy in an AC circuit. Electrons can act as wave medium). If it is true, How does EM energy travel in space. Can gravity act as a...
22. ### Electromagnetic energy wave (photon) questions

some questions that have been bugging me: 1.Is there a beginning and an end to a photon? Does it take different amounts of time for different wavelength photon energies to be absorbed? would for example a radio wave photon be absorbed at a slower rate than a higher energy/frequency gamma...
23. ### Electromagnetic energy saving space shuttle

electromagnetic energy saving space shuttle! hey! i found that if electromagnetic generators(made of superconducting wires) are enclosed in freezing nitrogen atmosphere(i.e at very low and constant temp.) in absence of any strong electric and magnetic field,maximum electric supply can be...
24. ### Electromagnetic Energy: Existence, Measurability & More

We are constantly surrounded by electromagnetic energy, right? In what way does this energy exist? Is it measurable? Is there much of it? Side thought, hypothetically, with a pole extended from Earth to outside Earth's atmosphere, couldn't the friction on the pole from "space" be converted...
25. ### Electromagnetic energy is not Gauge invariant?

I assume I am making a mistake here. Can you please help me learn how to fix them? In electrodynamics, the gauge transformations are: \vec{A} \rightarrow \vec{A} + \vec{\nabla}\lambda V \rightarrow V - \frac{\partial}{\partial t}\lambda These leave the electric and magnetic fields...
26. ### Electromagnetic Energy & Oxygen

First off, I know nothing about physics so if this question seems bizarre, that's probably why! In theory, are there conditions that would permit electromagnetic energy to block or limit the passage of oxygen (normal, everyday oxygen levels)? Is electromagnetic energy denser than oxygen under...
27. ### Question about Electromagnetic Energy

In his Lectures on Physics, Feynman derives the electromagnetic energy density u and the electromagnetic energy flux \vec{S}. However, he states that there is an ambiguity in the field energy: the common expressions given for u and \vec{S} are only the simplest known expressions. There are...