Radiation Definition and 1000 Threads

I have 2 questions about EM radiation produced by an occilating electric charge. Q1: With graphs of electromagnetic fields, you can see that it contains an electric and magnetic component. What does these mean or give information about? Q2: By occilating the charge, you will get such a graph...

I'm curious about that do gases emit infrared radiation the same way as solid bodies do? If yes, how can it be detected like an infrared camera does?

Homework Statement The peak of the thermal radiation power spectrum (dR/dλ) is at a wacelength of about λm=hc/5kT. Why is the peak of the same power spectrum plotted as dR/df not at fm=c/λm= 5kT/h? Homework Equations dR/dλ= 2πhc2/(λ5(e(hc/λkT)-1)) f=c/λ The Attempt at a Solution

Homework Statement A python can detect thermal radiation with intensity greater than .60 W/m2. A typical human body has a surface area of 1.8 m2, a surface temperature of 30°C, and an emissivity e=0.97 at infrared wavelengths. What is the maximum distance from which a python can detect your...

Hello When virtuals particles appears near a black hole , the one with a negative charge is attracted by the black hole , and as mass is proportional to energy , the black hole "evaporates" . My question is , why the particle attracted is always the one with the negative charge , is it because...

Hello, Does anyone shield themselves from computer / monitor from EMF radiation? if so what materials do you use to cover/coat your electronics? I am buying an EMF meter soon (Trifield 100XE) and plan on solving all my EMF issues, specifically around my computer tower, monitor, and other...

Imagine there is a semi-infinite semi-transparent body--such as a glass--at some temperature T. No surfaces exist. What is the energy intensity of thermally emitted light from any point in the body? If you use an absorption or emission coefficient (as I suspect is correct), can you explain how...

Guys, I'm looking for some checking of my own understanding about the EM waves given off by accelerated particles. Specifically, is this radiation only due to disturbances in a previously static electric field...therefore we are viewing this disturbance as a wave? Or, is there more to the...

Homework Statement Energy can be transmitted via radiation, the rate at which this happens is H=σAT4. A bar of iron is 0.5m long, 0.2m wide and 0.2m high. Iron has a density of 7900 kg/m3, a heat capacity of 400J/kgC, and a coefficent of linear expansion of 1.2x10-5 What is the rate at which...

An article in Wikipedia tries to explain pigments. One particular section has the following: "A wide variety of wavelengths (colors) encounter a pigment. This pigment absorbs red and green light, but reflects blue, creating the color blue." Questions arise... They may see stupid, but please...

excuse me if this is too basic question. why is it that black materials BOTH "absorb" and "radiate" more heat ( energy ) and white materials do it less. i mean is there a rule that any material absorbs and radiate heat in the same amount and can't absorb more (like black materials) and...

Hi, Situation A: Black radiator in a room with white walls. Situation B: White radiator in a room with black walls. Which one is the most efficient situation? I know that convection is dominant if you look at a radiator, but i would like to know the answer in terms of radiation. Thank you :)...

It is said, that in the beginning the universe was a singularity and then it exploded. A picoseconds or so after the explosion it was a fiery ball trillions of degrees in temperature and containing pure radiation. as it expanded it cooled down until quarks and then barons and other particles...

Hi everyone. On these days, by watching solar panels and similar stuff, I just thought about it, and why they take such a wide surface to produce energy, and why their output is often low, as we all know. By navigating here on the internet, I've just seen a device called OPO (Optical...

Light hits an object and gets reflected back to our eyes and we see its color. But it also emits Thermal Radiation, so technically it should be 'emitting' both of those light waves at the same time. When iron gets heated up we only see the red color being emitted because it got heated up. What...

I hypothesize that I can measure an increase in background radiation due to cosmic rays from ground level in Utah to 10,000 ft altitude with a Geiger Muller set-up. I feel that I have enough information to order equipment now (a working knowledge of gm tubes, energy levels of & the special...

I have limited physics knowledge, but I have always been interested in the physics and I am an industrial radiation safety officer with an engineering background.Have there been any experiments in respect to measuring half life with large variance in gravitational fields? Although half life may...

Hi, I have a simple question that will probably have a simple answer. If the Big Bang was a finite event (i.e. took place over a certain amount of time) why is it that the background radiation from it as sensed on Earth (TV static) is continuous? Will it continue to be continuous forever? How...

Can you produce a safety poster for the handling of radiation for first time users, explaining the ways to handle it, the implications of handling it incorrectly and anything else you think is necessary, for a level science, desperately need a kind sole to show me the way xxxx

Homework Statement I have data of an experiment to find absorbtion coefficent of a sample. one curve shows intensity of original beam, the other one is intensity with sample (with wavelenght). Here is the data : Homework Equations Where: I = the intensity of photons transmitted across...

Dear All, Can someone give me an intuitive idea of the acoustic radiation force. I have read from a paper that the acoustic radiation force generated by a standing acoustic wave is larger when the size of particle is smaller than the acoustic wavelength as compared to the case when size >...

I've heard of the muons and electrons that constantly hit Earth's surface in cosmic rays coming from extra terrestrial particles that break up in Earth's atmosphere but I was curious what factors played a role in the type of radiation produced from these particles in the atmosphere (i.e. More...

Maybe this article is more readily available than I'm aware of but thought it would be of interest to some- 'The Quantum Mechanics of Black Holes' by Stephen Hawkings http://planck.phys.uwosh.edu/rioux/thermo/pdf/Black%20Holes%20--%20Hawking.pdf

hi , i am not getting how harmonic oscillator is linked to the modes of radiation field- as explain by Dirac in his quantum theory of radiation.

Is it accurate in any sense of the word to think of electromagnetic radiation, ala chapter 7-8 of Landau, and gravitational radiation, ala https://n.ethz.ch/~usoler/download/GR/Spacetime%20and%20Geometry.pdf , as the classical field theoretical analogue of inelastic (& elastic?) scattering, the...

In the view of Hawking radiation and entropy of black holes, the evaporation is continuous and at one point, there will be no singularity for the black hole. By relativity, if we reach a super massive black hole, then time would be relatively slowed down to a point that it stops (maybe?). Now...

A number of my relatives believe that radiation from cell phones is dangerous. After doing a bit of reading, I've found that the general scientific consensus is that this is not the case, and I myself don't see how low power, low frequency, non-ionising radiation can cause e.g. brain tumours -...

According to the documents I have read, Plank made two changes to Rayleigh-Jeans approach in order to produce an equation that matched the black-body radiation, experimental curves: 1) As a mathematical convenience he assumed that the oscillators in the walls of black-body cavity could only have...

The energy of photon is $$E=\frac{hc}{\lambda}$$ Now if we have an isotropic point light source of power P, Number of photons $$N=\frac{P}{E} = \frac{P \lambda}{hc}$$ Hence one can find the change in momentum and hence the force exerted by a beam or light sources. But let's say we keep an...

I know that entropy is a measure of disorder. But Entropy is also a function of the state of a system, and has a value determined by the state variables of the system. Does that mean Entropy describes the equilibrium state of a system. Please explain in layman terms in this context what is...

Thats my simple question!

Black holes are claimed to radiate at a temperature corresponding to the hawking radiation. But who is measuring the temperature? If the radiation is measured from far away the red shift will indicate a lower temperature won't it? Is the temperature given by the formula as measured from a...

I see that the formula for hawking radiation is related the the formula for unruh radiation. The accelleration experienced by a body yields an unruh temperature equivalent to a black holes hawking temperature with an equivalent value of g. The unruh effect happens at all accelerations, therefore...

Something I don't understand is how the energy is subtracted from the black hole. So let's say one pair of virtual particles pop up on the event horizon, the particle goes in, the antiparticle goes out. Then let's say that a second pair does the opposite. My first question is why is the...

Hi people, I have a problem with some integral here. I have a loop of radius a, with a current I = Ioe-iωt' and trying to calculate the radiating fields in the far zone, my procedement is: Current density: J(r',t') = Ioδ(r'-a)δ(θ'-π/2)e-iωt'/2πa2 φ (φ direction) Here t' = t - |r-r'|/c...

Hello, After researching on many kinds of confinement methods and most promising reactions, (aneutronic fusion etc.) I saw almost every paper complained about radiation losses as the greatest problem preventing net power gain. And except Tri-Alpha Energy and LPP (Dense Plasma Focus) companies...

I am at odds over how Hawking Radiation can cause a problem with entanglement - or even how the pair particle to a Hawking particle can enter a black hole. The notion behind Hawking Radiation, as I understand it, is that a particle divides above the event horizon creating two entangled...

Homework Statement One of our homework problems asks us to state the density of Baryons, Cold Dark Matter, Radiation, Dark Energy, and the total density of the universe in terms of the critical density today. It also states to give the density of each quantity in dimensionless Omega units (the...

I just saw The Theory of Everything, which is a Hollywood biopic about Stephen Hawking. Of course the physics content had to be watered down and made to serve dramatic and thematic purposes, but a couple of historical points seemed interesting and made me wonder whether they were real: 1...

I currently watched a video on youtube about Casimir effect and here's the link The professor in the video talks about Casimir effect and Hawking's black hole radiation While talking about black hole radiation, he says that mass of black hole decreases if some particle or antiparticle loses...

If you only knew the temperature of the black hole, like, if for example, the temperature of a 4 solar mass black hole being around 1.5e-8 kelvin, how could you possibly be able to calculate what wavelengths of radiation the black hole would give off? Would a black hole like this really only...

Homework Statement Two large plates are parallel and close to each other, vacuum is between them. they are held at 2000K and 3000K. What is the energy transfer rate between them. Homework Equations The energy emission rate per unit area-the Stefan-Boltzmann Law: $$R=\varepsilon\sigma T^4$$...

I just read the following about the evolution of stars: "When reaching point 2 in the HR-diagram, the radius of the star has been increasing so much that the surface temperature is close to 2500 K which is a lower possible limit. When reaching this limit, the dominant mechanism of energy...

The spectral radiance of a blackbody has units of W·sr-1·m-2·Hz-1. How do I deal with these units if I want to think about a 2D problem of radiation in Cartesian coordinates? I assume that instead of a sphere of emission (which would result in artificial decrease in intensity with the inverse...

Homework Statement For a fixed given electrical power to two monopole sources, producing the same frequency. Which mode, either in-phase or out of phase, will radiate the most sound power into the far-field? Homework Equations Is the radiated sound power dependant of the given electrical...

why it is said that human eyes are unable to see ultraviolet radiation.sun emits ultraviolet radiation ,when we try to look at sun ,we see light coming from it (it is another thing that we can not resist that light longer and eyes shrink and we eventually have to stop doing so)but we do watch...

I'm trying to understand the issue of CO2 and global warming better. Can anyone explain to me the mechanism by which CO2 in particular converts infrared radiation to heat. I've had a semester of college chem and three semesters of physics, but I'm not sure what theory I should be able to use...

I am having some issues with the derivation of the Planck Radiation Formula, as for instance given in http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html . My point is that the assumption of cavity modes implies the formation of standing waves inside the cavity walls. In most situations in...

Why and how does a neutron knock electrons off of atoms? Is it because a neutron is not exactly neutral? Is a neutron composed of smaller charged particles which interact with the electrons when it gets close?

1. Homework Statement Hi, I have to do lab experiment - estimating infrared wavelength (from remote control). My experimental setup includes CD, remote control, webcam (without IR filter, so I can see the infrared radiation), sheet of paper (I will see diffracted light spots on it) with hole...