Radiation Definition and 1000 Threads

Hello all, I have a problem with a typical style of problem I seem to always struggle with. Just to clear this up, I am studying for my comprehensive exams later this summer. So I am going through past problems to bone up on the last two years of grad school. At which point I came across this...

My spouse has severe OCD and radiophobia. I realize this is not exactly the most appropriate venue for our questions, but hopefully somebody can help us in the right direction. She noticed several small (3-5mm), circular petechiae in a regular pattern across a roughly 6x6in area on my left...

Homework Statement X-ray pulses, visible-light pulses, and radio pulses (the latter corrected for dispersion in the interstellar plasma) emitted by an astronomical object called a “pulsar” are all observed to arrive simultaneously at the Earth — with an uncertainty of only 200 microseconds. The...

Hello everyone, I want to calculate or rather simulate a particle movement by influence of a ultrasonic wave. I have read many times that I have to use the acoustic radiation force for calculating the movement of a particle but not why? At first I calculated the particle movement only with...

There is Hawking radiation associated with black hole event horizons. And there is Unruh radiation associated with horizons produced by acceleration. I've also heard some suggest that there is radiation associated with the cosmological event horizon due to space itself accelerating in its...

If intelligent life had evolved on some planet 6.8 billion years ago (half the time to the big bang 13.6 bilion years ago) and they had sent the equivalent of the COBE / Planck satellite to map the cosmic background radiation, where in the electromagnetic spectrum would they have seen the...

Recently I was actually stuck on a thought about hawing radiation. If quantum fluctuations cause virtual particles to occur from space. So, to maintain the balance of mass in the universe, the particle with -ve energy should be having -ve mass, right? If so, by Newton's equation of gravitation...

Cherenkov radiation is described as being generated by a charged particle moving through a dielectric medium with a velocity greater than c/n, where n is the refractive index in that medium. Since n varies with frequency, there is a cutoff where n drops below 1 and no radiation is emitted above...

This is something that has really been bugging me lately. There was a study from over twenty years ago that proposed that electromagnetic radiation might have been able to pass from one end of the universe to another in the early universe, furnishing an explanation for the homogeneity of the...

Hi guys I'm not going ask is radiation from phones and masts safe, half would say it's absolutely safe and half would say it's probably a bit dangerous. My question is how does phone mast radiation compare to mobile phone radiation, broadly speaking of course. I'm moving house soon and there's...

CMB was created 380k years after big bang. Then photons were released in the creation of hydrogen. How can we still see them today? Would they not travel fairly straight forward out of our universe and never return again?

Correct me if I am wrong, but my basic understanding of how the Chronology Protection Conjecture (CPC) would work is that, as virtual particles created from the quantum fields of the vacuum would traverse a wormhole and arrive in the past, they would then travel back into the wormhole alongside...

Hello, I'm an English student and external candidate, hoping to take my Physics with me through life. I have some questions regarding a topic I'm researching, currently. I have a book "Advanced Physics - Steve Adams, Jonathan Allday", which details 'Blackbody Radiation', as evidence for a...

well, this may be obvious for many of you guys here! and I know it must be! but I don't seem to find any satisfying answer online. well, I know that when you heat up any kind of matter it will emit light depending on its temperature, for example, humans will emit infrared light the same as...

Since NASA is currently under way with the deep space Ion drive, they plan on using xenon to power this propulsion system. My question is could they harness the already existing radioactive particles in space to power it? If they could then there would be almost an unlimited supply of fuel for...

Homework Statement If a proton with a kinetic energy of 6 MeV is traveling in a particle accelerator in a circular orbit of radius 0.75m, what fraction of its energy does it radiate per second? m = 1.67 * 10^-27 epsilon_0 = 8.854 * 10^-12 c = 3 * 10^8 Homework Equations dE/dt = (q^2 a^2) /...

Homework Statement I(λ, T) is 4 pieces multiplied: (8π/λ4) (hc/λ) (1/(ehc/λkT-1) (c/4). 1. Identify the meaning of each term. 2. Which term(s) fix the ultraviolet catastrophe? The Attempt at a Solution Well I know that the energy of a photon is given by (hc/λ), and I'm fairly certain it was...

I'm trying to find out how much gamma-radiation the average human is exposed too from background radiation. But all I can find are numbers describing the total background radiation, not just the gamma radiation alone. Does anyone know where I can find this information?

Homework Statement What is the intensity of solar radiation in a place where is the full moon ? I know luminosity of the Sun and Earth's distance from the Sun RE and Moon´s distance from the Earth RM. Trajectory of Earth and Moon are circular. Homework Equations distance of the site from the...

What is the necessary and sufficient condition for an electron to radiate? How many methods to cause an electron to radiate?

Homework Statement A wooden box is painted completely with black paint. The interior dimensions are 18”x24”x3.5”. The bottom and sides are made with 9 pieces of 2x4 douglas-fir-larch dimension wood lumber. The top of the box is open and is covered with 0.118” thick clear acrylic. The acrylic is...

In an attempt to explain why a matt surface of aluminium is a better emitter/absorber of blackbody radiation than shiny surface of aluminium, my university lecturer suggested to me that: By brushing a metal surface to create a matt finish, the surface of the metal becomes rougher. Rougher means...

I was thinking about the title but after searching Arxiv, PF and the internet in general, my confusion has only increased. I have a few questions: 1. Often I see units where ##G=c=\hbar=1##, but what is the charge of an electron in these units? Everyone says M=Q as if it was somehow obvious how...

I have that the energy density of matter approx 0.3 , so this is measured by galaxy motion / gravitational lensing etc, that's fine. I have that the energy density due to the vacuum is 0.7, so this is measured by the expansion rate- the common suspect being dark energy. I have radiation...

What happens to an electron after it has undergone Bremsstrahlung and all its energy has been converted into an x-ray photon?

A blackbody is also a perfect emitter giving off electromagnetic waves at all frequencies. A detector could measure the intensity of the radiation it receives through the prism. By moving the detector to different positions, you could measure the intensity of light as a function of color or...

Is there any way to convert ionizing radiation to electric energy without converting it to heat in the meantime? I don´t mean avoiding losses as heat - these are unavoidable - but direct conversion of some energy to electricity, by a mechanism that does not depend on buildup of heat. For...

Homework Statement Calculate the absorbed dose of radiation for tissue that suffers a mean energy absorbed of 420 Joules in a quantity of tissue that has a mass of 60g. Homework Equations This is really my question. No relevant equation is provided in these materials so my independent...

The universe is believed to be 13.8 billion years old and at least 45 billion light-years in radius. Now there is also a black hole at the center of our galaxy, with my basic understanding of black holes I understand that this would warp time and space, is it possible that it's warped so much...

Hi guys I´m doing an experiment in thermocouples electricity generation by thermal radiation of Sun (As an addition to Solar panels). I´m still in high school and I don´t know a lot about the topic. I would like to simulate sun thermal radiation with a 100w incandescent light bulb as an...

Why does fission/fusion occur instead of alpha/beta/gamma radiation?

How would one go about determining the amount of heat generated by the decay of a radioactive particle, such as Cesium 137, Polonium 210, or Strontium 90? How would you determine how much of the radioactive material would be needed to heat, say, a cup of water to a certain temperature, taking...

Hi! Could someone explain to me why an electron at rest without any influence from a magnetic or electric field cannot emit a photon ? Could you explain it mathematically too ? Thanks in advance...

Light speed is the maximum speed within spacetime so the universe is limited by the speed of light.. supposed there was a signal that is faster than light.. do they have corresponding radiation that we can detect.. for example.. some black holes in center of galaxies are billions of times the...

When reading about this subject on the internet, I found two ways how it works and I don't know which one is correct. 1: A particle pair is created near the black hole horizon. So there is an antiparticle and a particle. The antiparticle gets sucked into the black hole but because the...

Homework Statement For school I'm doing a project on hawking radiaton but I have very big difficulties trying to understand it. I'm trying to understand the matter about: Unruh effect, particle pair (antimatter - matter) and the theory of relativity regarding vaccuum. Homework Equations none...

I am an undergraduate student of a university, I have taken the research topic as Study of Rotating black holes and Hawking radiation which I am really interested. Research description as follows. The geometric invariant are computed in various black hole geometries in several different...

Hi, So I can get the idea that the ac current in a radio transmitter produces radio waves of the same frequency of the ac supply, just like shaking a slinky sprung up and down but how does this translate into the radio waves as actually coming out as photons and for that matter other than...

Hello, I am trying to figure out how much the human skin temperature would increase when the skin is illuminated by radiation of a certain intensity (W/m^2). We can assume that the skin has an emissivity and absorptivity both equal to 1. For instance, imagine the skin illuminated by the sun (I=...

When begin the radiation epoch with scale factor ~t1/2 ? I read in some text that this begin at Planck time, but in other texs says that begin approx at 3 minutes.

Okay... I have two questions regarding thermal radiation...The first one is that, it is a constant fact that heat travels from hot to cold body, and all things give out thermal radiation, So arent these two facts contradictory in the sense that "everything is heating every other thing regardless...

Can I confirm that the background radiation is from out of our galaxy?

Hello everyone, I am working on understanding how Kirchhoff's Radiation Law applies in the real world. Basically, the absorbed solar radiation must equal the thermal radiation if a surface is to be at equilibrium. Certain relationships follow from this assumption, namely, for an opaque...

I'm sure that there are limits to the analogy between the event horizon of black holes and the "Rindler horizon" for an accelerated observer, but there are a number of similarities: For Schwarzschild spacetime as described in Schwarzschild coordinates: Spacetime is static, and a rocket must...

Hello everyone! Im a newcomer, a teenager who has countless doubts with respect to relativity, quantum theory etc. But these two questions bother me the most: 1) Hawking radiation states that when the separation of a particle (eg. a photon) into charged particles happens in the event horizon...

Homework Statement By applying the first law to a quasi static process, show that the entropy can be expressed as S = (16σ/3c) VT3 Homework Equations U = 4(σ/c) VT4 PV = 1/3 U[/B]The Attempt at a Solution I know I should be using dS = dQ/T but it's unclear to me how to use this unless I...

Hi folk, i need an help for this esercise. 1. Homework Statement Determines the rest mass lost by the sun every second for emission of radiation. It assumes that the surface temperature of the sun is 5700 K and the diameter ##D_s=1.4 × 10^9 m##. The Attempt at a Solution The solar nuclear...

The following are a few questions to help me understand the variability of views about Hawking radiation held by various knowledgeable PF QM physicists. 1. Do you personally believe that Hawking radiation is a real phenomenon rather than a only a theoretical possibility? 2. What percentage of...

Hello, I am rather new to Physics and for a class project on exponential growth and decay in nature and I chose the effects Hawking Radiation on black holes. If anyone could help explain how the mass and temperature change over time and how to calculate them(this one especially) that would be...

**For example, drying a surface --> I know it has an effect on the skin, but if it were contained and blocked from sight, would it still leave any radiation emissions on any hard surface??