Em radiation Definition and 89 Threads

I understand that em radiation (light) will be produced if you cause a charge to oscillate. Does this happen at all frequencies? If I charged a comb by running it through my hair and then shake it up and down, am I sending out light waves?

Have viewed PF, first time post (have searched for this question on forum): The energy of EM radiation can be described by the Poynting vector S = E x B (insert conversion factor for cgs, MKS, etc). For a traveling EM wave, what happens to the instantaneous value of S when E and B are...

It is my understanding that electromagnetic radiation is absorbed by an electron and then emitted at another angle. So why does particle size affect scattering when the phenomenon involves electrons? Also, why does the size of the wavelength of the light relative to the diameter of the particle...

Homework Statement A particle of mass m and charge q is attached to a spring with force constant k, hanging from the ceiling. Its equilibrium position is a distance h above the floor. It is pulled down a distance d below equilibrium and released, at time t = 0; Under the usual assumptions...

I was always told that EM radiation is a far field effect. Does this mean that the light emitted from the accelerating electron is not right next to the electron but a little further out. And also how do you calculate the frequency of the light coming off. When I looked through Griffiths...

I would like to know whether Kelvin or KJs matter when it comes down to a material radiating and / or conducting its heat.

Why does a moving particle particle emit EM-radiation?

If photons "carry" visible light, and light is just a specific frequency of EM radiation... who carries radio waves? [PLAIN]http://www.antonine-education.co.uk/physics_gcse/Unit_1/Topic_5/em_spectrum.jpg And can an EM radiation at specific frequency be changed to a different frequency? I...

Organisms radiation EM energy. I am aware of the brain and nervous system as a source (because of electrical currents, etc) and that we have a lot of IR radiation. Is the majority of the energy due to blackbody radiation, a by-product of chemical reactions, or something else?

Since a changing current creates a magnetic field, and if there's a wire near by, the magnetic field will induce a current in that wire. What is needed / what does it take to turn that magnetic field into EM radiation such as a radio wave? Or is it purely just the frequency of the current, so...

Aight, so I have this problem where I think about something and then I understand it, but then instead of stopping thinking and understanding it, I keep thinking and stop understanding it. Unfortunately then my poor brain is so confruzed that I am unable to backtrack to understanding, and I...

Hello everyone, I'm a bit confused about electric dipole radiation. In my E&M book "Intro to Electrodynamics" by David Griffiths, it states that the electric field from an oscillating dipole is in theta hat direction. Mathematically I have the proof as to why in my book, but conceptually I'm...

I see everywhere the explanation that electromagnetic radiation self-propagates this way: a changing magnetic field induces a changing electric field, which in turn induces a changing magnetic field and so on and so on. I do not understand that. I do not have a problem with saying (it is a...

Both Wikipedia and my educators called electromagnetic radiation a self propagating wave. I would suggest that the word self be removed from wikipedia at least. There is no self in a wave. Even the word "coupled" or "causally related" are risky WRT the grav and mag components as I don't...

Goodday. In my introductory course of Physics, we use Serway. I've typed over a little piece from the book that I find quite vague. It is giving an example of (after deducing the plane wave EM equations) EM radiation. It uses the following antenna: The positive and negative sides are...

I've read that even before the 20th century physicists realized that light carries momentum, and that - although experiment is the ultimate arbiter in science - one can arrive at this conclusion by studying Maxwell's equations alone. If this is the case, could someone give me an outline of the...

Homework Statement http://i258.photobucket.com/albums/hh258/Plutoniummatt/Untitled-1-2.jpg Homework Equations Pwr Ref Coeff: (Z'-Z)/(Z'+Z) all squared I maybe made a mistake but i can't spot it. And its bugging me I did square the whole thing afterward for the power...but...

As grotesque as the title may appear to suggest, I basically want to understand just that. Why is it that EM radiation of each group of wavelengths (visible, IR, UV etc.) manages to penetrate materials with varying ease. From what I've seen so far - and I haven't studied this directly, I'm just...

Hello everyone! Let me first say how cool it is that this forum exists, I wish I'd thought of coming here years ago. I am trying to understand how EM radiation works. From the high school physics that I've learned I have been under the impression that reflection was due to electrical...

Homework Statement Two incoherent EM waves of intensities 10I0 and 14I0 travel in the same direction in the same region of space. What is the intensity of EM radiation in this region? Homework Equations I = I1+I2 + 2√(I1I2) or I = I1+I2 - 2√(I1I2) The Attempt at a Solution I...

Hello, The city added a new electric transformation station near my house and has recently closed down a kindergarten adjacent to it due to 'radiation safety' reasons. My house is two doors down and my mother is concerned that radiation from the station might be hazardous to her health. She...

Homework Statement A certain star is 13 million light-years from Earth. The intensity of the light that reaches Earth from the star is 6 10-21 W/m2. At what rate does the star radiate EM energy? Homework Equations i know you have to convert lightyears to m. (1.23e17m) multiply this...

Anybody knows if there is a rule for EM radiation cross over materials ? The wavelenght in comparison the size (or structure) of molecule is determinant ? Ex. why infrared pass through the concrete but not metalics ? Thank you.

Does a stationary charge emits electromagnetic radiation? Does a moving charge in magnetic field emits electromagnetic radiation?

Hello, Is there any empirical evidence that electromagnetic radiation produces gravitational fields? I understand that as a form of energy it is expected to induce a spacetime curvature, but has this prediction of GR actually been tested? Is it at all subject to any controversy? Thanks, Armin

What are the ways (both natural and artificial) in which em radiation is generated? Here is one of the methods: We take a point charge (or more practically a charged sphere with uniform charge distribution) such that we can voluntarily fluctuate the amount of charge on it. We fluctuate the...

There is a EM radiation of frequency suppose x Hz.Let it has to travel a distance of y m.Now what's the time required for the radiation to travel the distance?The question seems to be very easy, but my confusion is in how can the frequency,distance,speed and time can be related? Can someone give...

OK so I'm familiar with the idea that EM radiation propagates through space in straight lines at a uniform speed, that of light. The idea that light moves in waves, that each wavelength carries a uniform energy and that the wavelength differs yet because the same speed is maintained each...

Helpppp please. EM Radiation doesn't make sense to me Hi. I don't see how you would get the answers to these questions. 1) A beam of light is shone on two sheets of paper, one of which is perfectly absorbing black and the other perfectly reflecting white. If the radiation pressure on the...

As I've been studying up on EM radiation, I've come to the conclusion that radio and light waves are not the same thing. Radio seems to be nothing other than a continuously flipping magnetic field (source: http://www.pbs.org/wgbh/aso/tryit/radio/radiowaves.html). In this way, there do not seem...

I'm bit confused about using terms temporal coherence and transverse/longitudinal spatial coherence when speaking about electro-magnetic radiation. I have understood that temporal coherence basically means how monochromatic light is. But I don't understand why temporal coherence is related...

Hi All, I've been recently reading a thread, and a question keeps popping up there. Its not very difficult, it just requires a simple yes or no answer...in a single photon emission, is the energy of the photon distributed evenly on the sphere r=ct, or does this sphere represent the...

Maybe the wrong word but can you get electromagnetic radiation in any frequency or is there a "quantum" frequency for which all other frequencies are some integer multiple? Related question - is there an absolute low and high frequency?

This should be possible with table top experiments rather than LHC scale experiments:abstract: Electromagnetic radiation decays with 1/r in three dimensional space, while the non radiating Coulomb field decays faster with 1/r^2. The general expressions for any dimension are 1/r^{(d-1)/2} for...

Electromagnetic wave are said to travel with velocity c, in vacuum and are also said to be a transverse wave. But consider this: Let a positive charge Q be at point P of a three dimensional space. Let this charge, at time t=0, begin an uniform circular motion with angular velocity OMEGA =...

hi , got 2 question about radiation: 1. Microwaves , radiowaves ,gamma rays and visible light - which one cannot detected by film? 2. Gamma rays , beta rays ,neutrons and alphas - which one has the shortest range in tissue ?( assume equal enegy) thanks

hi guys, having a bit of trouble answering this physics question. Wondering if any of the experts can help me out. Can the electromagnetic radiation produced by a hot gas of hydrogen atoms be exactly of one frequency? They say also that the atoms make a transition from state n=2 to n=1 and...

hi guys, having a bit of trouble answering this physics question. Wondering if any of the experts can help me out. Can the electromagnetic radiation produced by a hot gas of hydrogen atoms be exactly of one frequency? not sure if this is true or not. They say also that the atoms make a...

Can the electromagnetic radiation produced by a hot gas of hydrogen atoms be exactly of one frequency? Assume that all of the atoms undergo a transition from the state n=2 to n=1. Note that the atoms in the gas are moving.