Emission Definition and 567 Threads

I was looking for information on how the photo electrons are emitted when under X-ray radiation. In this ancient review paper here http://journals.aps.org/pr/pdf/10.1103/PhysRev.30.488 they state that the most common angles for non polarized X-ray beams (of various energies) range roughly at...

A friend is a quantum chemist. He is in agreement that climate change is bad (he feels the primary problems with CO2 is ocean acidification). Anyway he states there is no credible research showing that atmospheric CO2 re-emits radiation to the planet. His belief is that the intersection of IR...

Dear Forum, An object, like a metal, that is highly reflecting (white body) is very different from a very emissive object (black body). An object that closely behaves like a black body absorbs all the incident radiation. But it also "emit" all the absorbed radiation (over a range of...

To estimate polarized emission from the galactic dust, BICEP digitized an unpublished 353 GHz map shown by the Planck collaboration at a conference. However, it seems they misinterpreted the Planck results: that map shows the polarization fraction for all foregrounds, not for the galactic dust...

Something I've yet to understand: If a molecule has a dipole moment about a given access than absorption of a photon can readily occur. However, if it is possible to preferentially orient molecules by applying an electric field, would the rate of absorption be greatly increased or decreased? It...

Light of constant intensity is incident on a metal surface, causing electrons to be emitted. State and explain why the rate of emission of electrons changes as the frequency of the incident light is increased. My answer: As frequency increases, energy of photons also increases, so more energy...

I was told at school that when a hydrogen electron gains heat energy enough to excite it shifts to a higher energy level, then after a very small period it falls back to its ground energy level, that means all the energy it gains should be lost, but if that is true since hydrogen has an electron...

I cannot wrap my head around this stuff. Sorry if long post. I understand that emission lines come from a higher energy state dropping to a lower state. This happens at discrete energy levels, which should correspond to discrete frequencies. And the same atom should be able to absorb photons...

Hi, i have a question here, but i don't know how to write a lengthened answer on it. I just know what happens and that's about it. Questions: A positron can be produced by pair production or by positron emission from a proton rich nucleus. a) Describe the changes that take place in a...

Three bodies 1,2,3 are in closed region. Region is at temperature ##T##. ##e_{\lambda,T}## - spectral emission power ##a_{\lambda,T}## - spectral absorption power In experiment...

Sorry about my poor English. I heard Jupiter emits lethal amounts of radioactivity (I don't know what kind). I also read things that suggested that there are areas where this radioactivity is more intense than on other areas. I wanted to know a few things: a) why does Jupiter emits so...

I understand that one can measure a single photon being absorbed using a photomultiplier tube or CCD. Can one measure a single photon being emitted by monitoring the current through an LED or the recoil of an emitting ion? Is it therefore possible to detect the same photon both being...

The Drude model of electrical conduction has the charge carriers being accelerated by an electric field and then interacting with the lattice ions. The cycle is then repeated. An unbound charged particle if accelerated emits electromagnetic waves. Does that mean that a prediction of the Drude...

Why don't electrons go into the next orbit during stimulated emission? Hey all, I was studying stimulated emission in lasers and I had a doubt regarding the same. When the electron collides with another which is in an excited state, why doesn't the electron, which gets collided, move into the...

i everybody i've studied in my 9th standard that x rays are produced when cathode rays(electrons) hit solid targets such as molybdenum,titanium,etc.. now we'll observe the physics going out there so what's happening there? an electron is coming with some speed say v and hitting the valence...

Hi everyone, I just wanted to double check on a fundamental concept of quantum physics. Let us consider a monochromatic beam of photons,incident on a material(of a finite thickness,say 15 cm.) which reflects, transmits, and also absorb photons. Now, in QED by RP Feynman it is stated...

I'm reading about electromagnetic waves and I can't make sense of their self-sustaining nature. If a charge accelerates for a moment and then stops a disturbance in the electric field is sent out. This changing electric field creates a changing magnetic field and they continue to sustain each...

The definition of the Gaunt factor. Hello. I'm wondering about the Gaunt factor. I'm currently interesting in the spectroscopy in which the Gaunt factor is the correction factor to the classical cross section associated to the photon with electron thus the corrected formula is the identical...

Hi, I am looking for online molecular emission spectra database for spectroscopic analysis of plasma. It would be great if searching in it is based on a wavelength of spectral lines/bands. For atomic spectra I found this database: http://physics.nist.gov/PhysRefData/ASD/lines_form.html But I...

Greetings PFers, I'm working on a project where micron size metal or plastic particles are carried inside an argon or nitrogen stream at ~1 atm. The particles travel through at 1/4'' ID nylon tube before they enter a chamber where they then travel through a pyrex tube. I have four 4'', 500W...

Homework Statement In a lab experiment on emission from atomic hydrogen in a discharge tube only a small number of lines are observed whereas a large number of lines are present in the hydrogen spectrum of a star. Why? The Attempt at a Solution I think it is related to temperatue but I...

I need help understanding the relationship between the excitation and emission spectra for a fluorescent material. This is not homework. Let's say we have the following graph which plots the two spectra for a given material: Two curves are shown - the excitation spectra and the...

When an electromagnetic wave is impinged on a semiconductor and we solve the perturbed Hamiltonian by taking into account the vector potential in the momentum term, two terms would add to the unperturbed Hamiltonian which one of them deals with absorption while the other with emission. I like to...

Something that bugged me when doing this lab. Standard little glass vials of gas, toss it in a 5kV potential make pretty color, look through diffraction grating see the individual wavelengths that are the finger prints of the element. My question however are all wavelengths equally...

I understand that in photoluminescence band edge emission in direct band gap semiconductors originates from the recombination of electron and hole in the edge of conduction and valence bands. However, recently I have stumbled upon near-band-edge emission, which seem to suggest the existence of...

why does the continuous emission spectrum depends only on the temperature of the solution and not on the characteristics of the source?i could not understand this.someone please explain me this:rolleyes:

I have read that relaxation of a rotational or vibrational mode in gases occurs through collisions of molecules , transferring energy of an excited vibrational mode into heat. But isn't it possible that an excited vibrational mode in molecules relaxes directly by emission of radiation...? I...

Why the light emitted in spontaneous emission is poly chromatic whereas the light in stimulated emissions is monochromanti? If E1 and E2 be two energy level such that E2 >E1, in both emission the energy difference is fixed, so the frequency and so the wavelength thus the light emitted in...

Hi there, In regards to the Spontaneous Emission of a photon from an atom, after that process occurs, is it possible according to the reversibility of the laws of Quantum Mechanics that the photon is re-absorbed by the atom? According to the reversible equation governing the process, would that...

Homework Statement A photon emitted during an electronic transition in a hydrogen atom has a wavelength of 486.2 nm. From what initial energy level (ni) did the electron transition? Homework Equations Energy = hc/wavelength (h = Planck's constant; c is speed of light; and wavelength is 486.2...

The electron needs greater energy than the work function in order to escape the material. But when it does escape, does it subtract the work function from it's kinetic energy or not?

I've often read that the emission spectrum of a fluorescent molecule is independent of the wavelength used for the excitation. But what happens in the case of a small Stoke's shift where the excitation and emission wavelengths overlap? If I use a narrow band excitation with a wavelength in...

Hi, I'm currently doing a course in particle physics at masters level and I have this problem: I know that having an red:anti-red gluon isn't possible as this produces an non-zero trace for its representation, but if I have a red quark that emits a gluon and afterwards is still a red quark...

hi all, i learned that only certain orbits were allowed in the atom and that if the electrons occupied any of the orbits in between, that they would no longer be in a resonance orbit (i was taught that the allowed orbits were the electron probability wave in resonance and therefore no EM...

I have data from exhaust gas analyzer, and I have to find the calorific value or the heating value of that particular fuel using that data. Can anyone show me how to do that please. Or if there is any other way to find the calorific value of fuel. The data is in the attached pic

I have a quantum harmonic oscillator at energy level n_1, and I want to know how much time will pass before it spontaneously drops to energy level n_2. I know about the position operator, momentum operator, energy operator, and angular momentum operators. Is there a "time until a system...

Hello everyone, a number of books and web articles says that the minimum field required is ≈10^7V/cm for electrons field emission/tunneling from the surface of metals. But fowler-nordheim formula shows that there is still considerable amount of field emission current density (mA/cm2) even...

Homework Statement Show that in the Bohr model, the frequency of revolution of an electron in its nth In classical physics, the frequency of revolution of the electron is equal to the frequency of radiation it emits. Show that when n is very large, the frequency of revolution is equal...

Homework Statement Calculate the wavelength of the Lyman-α line (the transition from the 1st excited state to the ground state) for (a) hydrogen atoms and (b) positronium e+e-, and explain the origin of their difference. In the light emitted from a star, a pattern of emission lines is found...

I'm in high school chem. and we are learning about nuclear chemistry (it's more of a physics topic in my opinion), but we learned that in beta decay a neutron loses mass (e- & anti-neutrino) and becomes a proton. We also learned that in positron emission a proton loses mass (positron &...

Typically (in popular literature) the process of photon emission by an excited atom is considered as an instant event. But actually it is quite likely that it is a continuous process. Such processes are usually described by evolutionary differential equations (ODEs or PDEs). Assume that we...

I have some questions regarding thermal radiation spectra of different objects. Is thermal radiation of objects due to electromagnetic radiation alone? Does my desk which is at room temperature emit as a blackbody with the proper factor for emissivity? Where is the "cavity" that the radiation is...

I'm studying spontaneous emission and I'm in trouble to understand the following: In a hydrogen atom we have distinct energy levels with different energy values associated to them. E1 = -13,6 eV E2 = -3,4 eV E3 = -1,51 eV To go from the first to the second energy level we need a photon...

Homework Statement Our quantum system has two levels: ψ1 = (1/\pi)1/4 * e-x2/2 ψ2 = (4/\pi)1/4 * x * e-x2/2 The energy of the ground state ψ1 is 0; the energy of the excited state ψ2 is \hbar * \omega0. What is the spontaneous emission rate for this system when it is in the excited state...

Homework Statement Sethna 7.7 Assume that the hole of area A is is on the upper part of the cavity, perpendicular to the z axis. The vertical component of the velocity of each photon is therefore vz= c cos(θ), where θ is the angle between the photon velocity and the vertical. The photon...

Not sure how to go ahead with this problem: Hydrogen atoms in a sample are excited to n=5 states and it is found that photons of all possible wavelengths are present in the emission spectra. What would be the minimum no. of hydrogen atoms in the sample? (sorry got nothin buzzin to attempt this...

I am having trouble understand why is true I would think that the rate in which N2 is changing is the rate of stimulated emission and spontanous emission together. Why is it just the rate of stimulated emission It is in the mathematical model section...

We're just been learning about emission and absorption spectra and how these relate to the energy levels of electrons in an atom but its brought up 2 questions. 1. In chemistry our notes say that the energy change between levels gets smaller as you move out from the nucleus, however in...

Hi I am trying to figure out if there is call for a small, commercial, educational radio telescope to measure the 21cm emission line of hydrogen. We have been developing an instrument with the following characteristics: - The antenna would have a size of about 1m x 1m. Because the...

I understand that light travels at “c” through any medium, and that the apparent slowing results from the absorption and re-emission of the photons by atoms in the medium. If this is the case, why, for example, are astronomers able to see the emission/absorption spectra of distant stars...