Questions tagged [electromagnetic-radiation]
Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.
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What is the relation between electromagnetic wave and photon?
At the end of this nice video (https://youtu.be/XiHVe8U5PhU?t=10m27s), she says that electromagnetic wave is a chain reaction of electric and magnetic fields creating each other so the chain of wave ...
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If photons have no mass, how can they have momentum?
As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects ...
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What are the various physical mechanisms for energy transfer to the photon during blackbody emission?
By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
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Why and how is the speed of light in vacuum constant, i.e., independent of reference frame?
I was told that the Galilean relative velocity rule does not apply to the speed of light. No matter how fast two objects are moving, the speed of light will remain same for both of them.
How and why ...
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Explain reflection laws at the atomic level
The "equal angles" law of refection on a flat mirror is a macroscopic phenomenon. To put it in anthropomorphic terms, how do individual photons know the orientation of the mirror so as to bounce off ...
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Why do prisms work (why is refraction frequency dependent)?
It is well known that a prism can "split light" by separating different frequencies of light:
Many sources state that the reason this happens is that the index of refraction is different for ...
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Does a charged particle accelerating in a gravitational field radiate?
A charged particle undergoing an acceleration radiates photons.
Let's consider a charge in a freely falling frame of reference.
In such a frame, the local gravitational field is necessarily zero, ...
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How and why do accelerating charges radiate electromagnetic radiation?
Let's consider it case by case:
Case 1: Charged particle is at rest. It has an electric field around it. No problem. That is its property.
Case 2: Charged particle started moving (it's accelerating)....
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Why is glass transparent?
Once I asked this question from my teacher and he replied "Because it passes light.". "And why does it pass light?" I asked and he said, "Because it is transparent.".
The same question again, Why ...
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Redshifting of Light and the expansion of the universe
So I have learned in class that light can get red-shifted as it travels through space. As I understand it, space itself expands and stretches out the wavelength of the light. This results in the light ...
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Phase shift of 180 degrees of transversal wave on reflection from denser medium
Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave, when reflected from an optically denser medium?
I tried searching for ...
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Electric field associated with moving charge
I have recently started to learn about the electric field generated by a moving charge. I know that the electric field has two components; a velocity term and an acceeleration term. The following ...
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Do two beams of light attract each other in general theory of relativity?
In general relativity, light is subject to gravitational pull. Does light generate gravitational pull, and do two beams of light attract each other?
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Is it really possible to break the speed of light by flicking your wrist with a laser pointer?
Minutephysics has a popular YouTube video called "How to break the speed of light". In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the spot of ...
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Why don't electromagnetic waves require a medium?
As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing ...
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Does a constantly accelerating charged particle emit EM radiation or not?
The Abraham-Lorentz force gives the recoil force, $\mathbf{F_{rad}}$, back on a charged particle $q$ when it emits electromagnetic radiation. It is given by:
$$\mathbf{F_{rad}} = \frac{q^2}{6\pi \...
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Why one should follow Snell's law for shortest time?
whenever two media and two velocities are involved, one must follow Snell's law if one wants to take the shortest time.
Why snells law must be followed to travel diffrent media in shortest time?
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Is the electromagnetic spectrum discrete?
I'm just starting to learn physics and I have a question (that is probably stupid.)
I learned that energy levels that the bound electron can have are discrete. I also learned that when an electron ...
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Amplitude of an electromagnetic wave containing a single photon
Given a light pulse in vacuum containing a single photon with an energy $E=h\nu$, what is the peak value of the electric / magnetic field?
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Explain how (or if) a box full of photons would weigh more due to massless photons
I understand that mass-energy equivalence is often misinterpreted as saying that mass can be converted into energy and vice versa. The reality is that energy is always manifested as mass in some form,...
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Why does wavelength change as light enters a different medium?
When light waves enter a medium of higher refractive index than the previous, why is it that:
Its wavelength decreases?
The frequency of it has to stay the same?
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Is there an infinite amount of wavelengths of light? Is the EM spectrum continuous?
The electromagnetic spectrum is a continuum of wavelengths of light, and we have labels for some ranges of these and numerical measurements for many.
Question: Is the EM spectrum continuous such that ...
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How do mirrors work?
My physics professor explained to me that electromagnetic waves are consisted of two components - electric and magnetic - which cause each other.
Which part of the mirror actually reflects the wave?
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Scattering of light by light: experimental status
Scattering of light by light does not occur in the solutions of Maxwell's equations (since they are linear and EM waves obey superposition), but it is a prediction of QED (the most significant Feynman ...
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Why does the refractive index depend on wavelength? [duplicate]
Why do different wavelength get impeded more or less when in different materials? Moving with the same speed, but a longer physical distance would imply that the fields oscillate less times in the ...
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Black body vs. Thermal radiation
I am seeking clarification of the following terms:
Black body radiation
Thermal radiation
Thermal light source
At the first glance, the first two are the same thing, and they are the radiation ...
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If you view the Earth from far enough away can you observe its past?
From my understanding of light, you are always looking into the past based on how much time it takes the light to reach you from what you are observing.
For example when you see a star burn out, if ...
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Are magnetic fields just modified relativistic electric fields?
Feynman's Lectures, Volume 2, says that the electromagnetic force is invariant in any reference frame, and the magnetic force in one frame becomes the electric field in another.
And Wikipedia says:
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What is the minimum wavelength of electromagnetic radiation?
As a first approximation, I don't see how a wavelength of less than 2 Planck distances could exist. The question is: Are there any other limits that would come into play before that?
For example:
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How is light emitted by an incandescent lamp?
I am looking for better understanding of how light is produced in an incadescent lamp. More specifically: how is the kinetic energy of electrons converted to light?
Are we dealing with interband ...