Radiation Definition and 1000 Threads

I'm a bit stuck here guys. I am but a humble computer scientist, so I'm hoping you guys can give me some insight. I have an IR sensor that's capable of detecting a target temperature (whatever it's pointed at) and the ambient temperature. I have objects (humans, hot mugs, etc.) sitting in front...

Hi, I got this fun idea. Has anyone ever consider that heat radiation could be an efficient propellant for a spaceship? Imagine a spherical spaceship, half of which is hot and with a large emissivity coefficient (say almost 1), and the other half is cold and with low emmisivity. A naive...

I know that a black body is an idealized body that absorbs all the incident EM radiation. And I also know that the BB emits a spectrum of thermal radiation that depends on its temperature. What I cannot understand is the re-emission. For what I've read, when in thermal equilibrium, a BB absorbs...

At one time, I read that the universe was, on a very large scale, essentially the same in all directions. Recently I have learned about the Cold Spot in the fairly uniform Cosmic Background Radiation map. Scientists have attributed the artifact to a very very large void in the ordinary matter...

I have been reading up on GR and for the life of me i can not understand how GWs travel through or distort space time, do they distort ST or do they travel with space time?

We see objects either because they emit light [particle or energy] toward us or because light bounces off them in our direction. This is true for all energy not just visible spectrum. We see stars because they emit light towards us and nebula because it is, generally, illuminated by some...

I've read that the Tsar Bomb used a lead casing for the second and third stages of the bomb instead of a uranium casing. A uranium casing would have resulted in fast fusion but would have created too much fallout. Typical Hydrogen bombs use uranium casings. A uranium casing would have indeed...

First time here, and looking for help on this. The 2nd part of this problem, I have seen some posts on and am still reviewing, but haven't found much on the 1st part. Homework Statement 1) Use l'Hopital's Rule to show that $${\lim_{\lambda\rightarrow 0^{+}}=0}\text{ and...

Hello everyone, Can alpha emitters cause nearby (gasses or air) to be excited and glow like Radium or Tritium? Is there certain chemicals (maybe like phosphor) that are suitable for it?

Hi all, I have a question concerning the derivative of the formula of the number of nuclei. I hope I've posted this in the right section, I'm new here :P. Anyway, in the question, the given values are: At a certain time t, there is an amount of radioactive Br-82. The activity A is 7.4*1014 Bq...

I might have learned what I am going to ask during my electrodynamics class long time ago but just that do not remember it now. I always wonder why does an electron moving in space with EM radiation have Hamiltonian of the form ## H = \left( \mathbf{p}-e\mathbf{A}/c \right)^2/2m +e\phi## where...

I want to calculate the radiation intensity of a cell phone which has a peak output power of about 2.0 W . The formula that I should use is I= P/A right? How to calculate the area if the question only state the distance which is 2 inch from the cell phone?

I'm doing high school physics and if a question says something like: A radioactive source gives count rate of 110 counts per second Can you say that the ACTIVITY is also 110 bq? My second question is how would a gieger counter detect gamma radiation? It is the least ionising of all three...

I am familiar with the explanations for atomic absorption and emission line spectra and how the existence of discrete, fixed energy levels can give rise to the absorption/emission lines that are seen at only very particular frequencies of EM radiation. However, I have no intuitive understanding...

Homework Statement A circular floor 9.15 m in diameter has an emissivity of 0.8 and is at a temperature of 29.4C. The floor is enclosed by a hemispherical metal dome which has an emissivity of 0.1. If the net rate of heat transfer between the floor and the dome is 660 W, calculate the...

Hi there, I'm trying to clear up some misconceptions I have about emission spectra from various substances. Most of the discussion about gases focusses on the line emission spectra from a hot, low density gas due to electron shell transitions. But I also know that any charges that are made to...

When the apparent horizon differs from the event horizon, as in the case of an observer falling into a black hole, does Hawking radiation take place at the former, the latter, or both?

hallo to all, i use a Radiation Pyrometer to measure temperature and Radiation Trough a datalogger i get those measurements in Volt i am able to convert the Volt back in the temperature but in Radiation it is more difficult i found the Plancksche function, but i do not really understand that...

No one seems to be bothered by this except me: Black holes have a finite lifetime measured in Schwartzchild time due to Hawking radiation. Similarly, the universe probably has a finite lifetime measured in Schwartzchild time. In that case, nothing ever falls through the event horizon of a black...

Hi, I am having some difficulty understanding some of the concepts in involved in Bremsstrahlung Radiation. I have recently been learning about the Rutherford scattering experiment where an alpha particle is fired towards a gold nucleus. In my book there is a fairly simple derivation of how you...

Homework Statement Find the electric potential of a point charge with constant velocity ##v##. Homework Equations $$V(\mathbf{r}, t) = \frac{1}{4\pi\epsilon_0} \int \frac{\rho\left(\mathbf{r}', t - \frac{| \mathbf{r}- \mathbf{r}'| }{c}\right)}{| \mathbf{r}- \mathbf{r}'|}d^3r' $$ The Attempt...

Hi! I have a question regarding the radiation coming from the sun. It might seem stupid to some people but I would really like to know how this works. When you see images of the sun's rays reaching the Earth for example on this image from wikipedia (see attached image). The rays are almost...

Hi all, Does electromagnetic radiation actually carry kinetic energy? Looking around the web gives different answers. I have seen explanations like radiation pressure experiments as evidence, but this has been argued being effects from energy absorbed by the recipient. In case it does not...

Hi, I am trying to understand what keeps getting referred to as "super radiance". So this has led me to R. H. Dickes 1954 paper "Coherence in spontaneous radiation processes". http://dx.doi.org/10.1103/PhysRev.93.99 . On the first page Dicke presents a "simple example", that is not simple at...

this might be kind of a weird question lol but according to forums on tortoises and other reptiles, ceramic heat emitters (a piece of ceramic heated to about 200 degrees id say) actually emit a UV radiation... is this true? where does the radiation come from? is it black body radiation...

Hawking radiation talk about particles emitted from black holes. Are the particles emitted are protons and electrons? (emitted at near light speed and gradually slowdown by gravity pull of black hole as the particles move outward to fill the interstellar space of the galaxy) If yes, that means...

Will a body of given emissivity kept inside a perfect black body start behaving as a perfect black body?

Homework Statement Given that we are working with biological samples of 5 and 10cm, is our assumption that the equation N = No e¯kt represents the radiation strength accurate? Explain. Homework Equations N = No e¯kt The Attempt at a Solution I'm completely stuck but... I believe it...

Suppose we have a closed system in which molecules cannot escape. Into this system we enter some radioactive molecules with \beta^+ decay. We know that the resulting daughter nuclide is also radioactive. We have some equations to describe the amount of parent nuclides and daughter nuclides...

Homework Statement Hi everyone, My problem is fairly simple: We have a circular current loop enclosing area A, and with a constant current I. The loop is rotating about its diameter at a constant angular frequency \omega. All we need to do is find the electric dipole, and magnetic dipole...

Hello PPer's, I have been considering the effect to which electromagnetic radiation emitted from stars might play in the gravitational coalescence of galaxies. Surrounding every galaxy there must be a halo of electromagnetic radiation streaming outwards at the speed of light which diminishes...

I know Density of energy is the amount of energy of photons per unit volume, but what do you mean by giving the range of frequency between f to f + df ?

What do you mean by the term "energy density of radiation " between the frequency range f and f +df ?

Is half-life inversely related to the radiation dosage of an element? That is, if an element has a longer half-life is it safer? If so, why is plutonium so dangerous, even though it has a very long half life

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...