Radiation Definition and 1000 Threads

Homework Statement We have a sensor onboard a satellite that is faced towards Earth, from the Sun. The LW absorptivity is 0.8 (a_LW) and SW is 0.2 (a_SW). I need to find a equation for the temperature as a function of time. Given datas is the Area=0.3 m^2 and Specific Heat of 4 J/K Homework...

bapowell submitted a new PF Insights post A Poor Man's CMB Primer. Part 2: The Birth of a Cosmic Background Radiation Continue reading the Original PF Insights Post.

Hello, new to the forum. I am currently in high school taking a full load of college classes through dual enrollment. I will graduate high school with an Associates of Science degree. I really enjoy math. It has always been my favorite subject. At the moment I am in Calculus 1 and it isn't so...

I'm not sure where to ask this question or if it even makes sense... Say an electromagnetic wave passes through a point in space. The point experiences some fluctuation of electric and magnetic fields. But what happens after the wave has passed? Are there any lingering effects, like a "wake"...

Consider a dipole antenna that is radiating at it's resonant frequency F. Consider an observer approaching this dipole antenna, in a direction perpendicular to the axis of the dipole, at velocity 0.6c. According to the relativistic doppler shift, the frequency perceived by the moving observer...

Q. Regards infrared radiation, conduction and convection, is infrared radiation the starting point, the fundamental source of heat energy (thermal energy), and the fundamental source of the other two? I’m thinking that the Sun predates the Earth by 30 million or so years so the first heat...

If only 14% of the total solar emission is in the UV region, why is ozone depletion a cause for concern. Considering that only a small fraction of the sun's total radiation reaches earth.

Consider the heat equation dT/dt - aΔT + v⋅∇T = S where S is a source term dependent of the radiation intensity I and the temperature T. The fluid velocity v is prescribed. We also consider the radiative transfer equation describing the radiative intensity I(x,ω,t) where ω is the ray direction...

I have no idea how lethal/strong space radiation is, but i do have an idea that most of it is from the sun perhaps? I also know that the prime factor to deflect this radiation is magnetic field and the ozone layer. I think the magnetic field handles only particle radiation and atmosphere handles...

How is a continuous chain reaction maintained within a moderator if it is not fissile material? Are the fissile materials mixed with the moderator or are they coalesced at the center of the surrounding moderator? If it is the latter, how would the surrounding moderator allow fissile material to...

The book is expensive, so I want a book like Bekefi's and Barrett's Electromagnetic Vibrations,Waves,Radiation. Preferably at a higher level than this book. Thank you!

I am currently confused with the concept of the blackbody radiation and the inverse square law. Planck's function for the radiation of a blackbody is in ##W sr^{-1} m^{-3} ##, is this somehow a form of intensity (because of the watts per square meter unit)? If it does, doesn't intensity...

Hello i have a question about cmb radiation.Cmb was release about 13.7 billion years ago and reach us from a point about 42 million light years.At the past were the age of the universe was smaller and the time that cmb release was smaller too,we were able to detect the cmb?I mean the cmb was...

Homework Statement The ice is placed in water, we know the surface area A, emissivity of both ice and water, Stefan-Boltzmann constant and the temperature of both ice and water. What is the equation for heat transfer rate between water and ice? Homework Equations Heat transfer rate by...

I'm very new to the understanding of Hawking Radiation. I don't know much about this theory, but I do know that Hawking radiation works on a Quantum scale. I know that with black holes this theory proposes th idea that over time black hole lose mass because of "Spontaneous appearing positive and...

Do just electrons emit photons/radiation. Or do atoms and molecules emit photons as well? Just can't get a clear answer on this. And if atoms and/or molecules also emit photons, can you please explain what causes them to?

I am trying to grasp the basics of Nuclear weapons and how they work, I understand the fission and fusion principles, but I am struggling with a basic question...Radiation. I am by no means a physicist nor an educated chap so please go easy on me. If it takes a tiny amount of Plutonium or...

Hello everyone, Can anyone assist me with the following; I have derived some very interesting cosmological quantities within regard to radiation as it moves through space. I am looking for someone trustworthy who can help me verify my work and point me in the right direction without claiming...

Hello, it is my first post created in this forum :) I'm interested in physics of radiation burn. How does it work? In my opinion high-energy particles (like photons, neutrons etc.) leave their energy inside human body (for example breaking bonds in DNA). This event trigger primary electrons...

A book I read says that when virtual particle-antiparticle pairs are created near a black hole then sometimes one of the particle pairs will be captured by the black hole while the other one will be freed to move away as a real particle - then this causes the black hole to lose mass and thus...

Please check my logic. 1. Hawking mechanism should give birth not only to photons, but also to their heavier analogs, Z for example. 2. Contrary to photons, massive Z bosons are not gradually red shifted, low energy Z simply fall back to BH, so the "red" part of the black-body spectrum of Z is...

From my understanding gamma rays can damage metal, making it brittle. Fortunaly, this appears to be little, but sill if you have a lot (like in p-D fusion) it becomes a serious hazard. The question is, how much? Specificly I need to know how much damange it does in compairison to Neutron...

Dear friends! What is your openion about validity of the following information: " When was the last time you checked your microwave for radiation leakage? Yes, I did say radiation leakage, because any microwave can start leaking radiation any time, for whatever reasons. And such a leakage...

Homework Statement ; attempt and equations[/B] Many times I face problems with a wire loop with some current (which may or may not depend on time, which may or not move) "flowing" in it. And I'm asked to calculate the radiation due to it. So using the multipole expansion I know that the dominant...

(sorry - not sure about the prefix) I have read that lead shielding is dangerous against high energy particle radiation because of the high atomic number in lead. The particles would have high chance of hitting the lead atomic nuclei and producing x-rays. I am fed up with moon landing...

Dear forum I am working with thermal radiation. This is the specific formula: P = σ ⋅ A ⋅ T4 P = emitted effect (W, J/s) σ = Stefan-Boltzmann constant (5,67 ⋅ 10-8) A = area of object (m2) T = temperature of object (K) How can I get to know the...

Homework Statement Two equal and opposite charges are attached to the ends of a rod of length s. The rod rotates counterclockwise at a speed ##\omega=ck##. The electric dipole moment of the system at ##t=0## is ##\vec p_0=qs\hat x##. Show that the electric field in the radiation zone is ##\vec...

I am trying to understand the formula's for Gravitational Radiation. At one point in the derivation, every source I have seen comes up with Kirchhoff's Formula but they never derive it. They always just say its a well known result from Electromagnetic Radiation. I have been able to determine...

A friend of mine heard a popular science show on the radio. A caller asked what is better to wear on a hot day, white clothes or black clothes. The answer given was that it did not matter because although black absorbs more readily it also radiates it more readily. My friend said of course that...

Homework Statement "The urban heat island (UHI) effect refers to the phenomenon of a metropolitan or built up area which is significantly warmer than its surrounding areas." Using white paint in roofs increases the solar reflectance and decrease the thermal intake into a building. Question:-...

So I realize that I'm probably wrong about this, but it seems to me that Hawking radiation cannot be emitted only at the event horizon. If we make the (albeit almost certainly wrong) assumption that the quantity of emitted particles is directly proportional to the potential for gravitational...

Homework Statement A ring with radius R has a constant current and is rotating around a diameter with constant angular velocity omega. 1)Calculate the radiation fields far from the ring. 2)What's the direction of the polarization for an observer along the axis of rotation? 3)What are the...

Hello. We're in the age of the high speed computation. Personal computer clock speed is on the order of GHz and scientist looks for a way to raise the speed up to THz class. I've read this from newspaper and got some question. I've learned in class that radiation effect becomes severe as...

The cosmic microwave background was a single event that happened literally everywhere in pretty much a single instance. That moment was in the past and is unchanging. What does change is the wavelength of the radiation as it travels through the expanding universe causing the wavelength to grow...

Hi, We are doing radiation analysis using solidworks simulation..And as a part of this project i need to validate it theretically..Hope i will get some help here.. Its cylindrical vacuum furnace,where inside strip type heating elements are placed which are connected to transformer of 60kW.After...

The black body curve of intensity vs frequency increases, reaches a maximum value and then decreases. As the temperature increases, the peak of the curve shifts to lower wavelengths or higher frequencies. 1) I only vaguely understand the relation between the nature of this graph and the fact...

I am reading the text 'thermal radiation heat transfer' by Howell et al. (2011). In it they describe normal spectral emission by an isothermal volume element dV as 4\pi \kappa_\lambda I_{\lambda b}(S)dVd\lambda where \kappa_{\lambda} is the absorption coefficient and I_{\lambda b} is the...

(note I am designing this question myself, in order to understand this phenomenon by example) Homework Statement Find the total radiative power emitted within a 0.1 m2 semi-transparent medium, having an absorption coefficient of 5 m-1 over all spectra, and a temperature of 1000 K. Note that...

I know that ozone on Earth absorbs ultraviolet radiation but chemical or material absorbs ultraviolet light like the kind in fluorescent light that absorbs ultraviolet light and reemits it as visible light.

Since Mars doesn't have a magnetic field of its own due to the cooling of it's core, what if you took a strong magnet from Earth say a superconductive magnet or electromagnet, will the small magnetic field (relative to mars) repel solar radiation, solar flares and other background radiation form...

Does activating flight mode help in reducing mobile radiation?

Hi, One of the main problems of the Rutherford model is the fact that the electrons are accelerated and hence should lose energy due to radiation. Bohr's model doesn't resolve this, it only postulates that the energy levels are quantized and energy can only be emitted or absorbed by jumping...

Hi All, I'm trying to understand the radiation mode of heat transfer. I have been reading the book by Incropera - "Fundamentals of heat and mass transfer" and have a few very basic questions. 1) Firstly, thermal radiation is the energy emitted by matter that is at non-zero temperature...

Hello, I just recently found out that one could find the Friedman's equation in Newton's approximation (without GR) by assuming that the universe in homogeneous and isotropic simply by using F=ma and the conservation of energy. On can then find that the scale factor goes as t^2/3, as expected...

I am looking for a reference describing the far-field electric and magnetic field of a dipole. However, I want a general formula for an arbitrary scalar function, and not specifically the usual formula which assumes a continuous sinusoid: $$ \mathbf{B} = -\frac{\omega^2 \mu_0 p_0 }{4\pi c}...

[unacceptable source deleted] Microwaves have a wavelength greater than visible light and are harmful. Ultraviolet light has wavelengths smaller than visible light and is harmful. In what ways are the two harmful and why isn't visible light harmful in the same ways? I'm a total noob. Just...

I want to get a half convex lens (thick in the middle, flat on one side). And coat it in thermally and optically reactive transition filters. They are to be segmented so to reduce spread of filtering. This will give a view of the sky with any bright light inhibited at the focus. Next to the...

I want to ask one question, in physics, we calculated acceleration of electron in a conductor, but according to classical electrodynamics, any charged particle while accelerating looses energy through EM radiations, So does these electrons also emit radiation, if not then please tell me WHY?

Suppose you have an RF generator feeding a vacuum system with argon ionized by that RF. With the tuner you see the VSWR is very good. That is version A, no ground or poor ground. Version B is the same thing, the container is stainless steel half inch thick to hold the vacuum. But in this case...

I want to know, excluding the sun with an appropriate boundary, whether it is possible for the balance of bbr to be positive for outerspace rather than on earth? I am thinking of a half convex with an active polariser across-the outer surface which allows through most radiation below the...