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 Chirped Pulse Amplification, and why is it important enough to warrant a Nobel Prize?
The 2018 Nobel Prize in Physics was awarded recently, with half going to Arthur Ashkin for his work on optical tweezers and half going to Gérard Mourou and Donna Strickland for developing a technique ...
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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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Why does NASA use gold foil on equipment and gold-coated visors?
I've read several websites about equipment covered with gold foil and astronaut helmet visors are coated with gold. However, their explanations are devoid of almost all physics content. Can someone ...
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What is an "attosecond pulse", and what can you use it for?
The 2023 Nobel Prize in Physics was announced today, and it was awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier, for
“experimental methods that generate attosecond pulses of light for ...
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Why does a remote car key work when held to your head/body?
I was trying to unlock my car with a keyfob, but I was out of range. A friend of mine said that I have to hold the transmitter next to my head. It worked, so I tried the following later that day:
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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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How many photons are received per bit transmitted from Voyager 1?
As of 2024, according to https://voyager.jpl.nasa.gov/ , Voyager 1 is around one light·day away from Earth and still in radio contact. When Voyager 1 sends messages to Earth, roughly how many photons ...
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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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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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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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Can photons be detected without being absorbed?
I am thinking about a detector that would beep if light passes through it. Is it possible?
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Why is light called an 'electromagnetic wave' if it's neither electric nor magnetic?
How can light be called electromagnetic if it doesn't appear to be electric nor magnetic?
If I go out to the sunlight, magnets aren't affected (or don't seem to be). And there is no transfer of ...
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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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Why doesn't the motion of a car affect the frequency of radio stations?
When we go in a car and tune to an FM radio station, why doesn't our motion disturb the frequency?
Like the Doppler effect?
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If visible light has more energy than microwaves, why isn't visible light dangerous?
Light waves are a type of electromagnetic wave and they fall between 400-700 nm long. Microwaves are less energetic but seem to be more dangerous than visible light. Is visible light dangerous at all ...
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How strong are Wi-Fi signals?
My family members dislike the idea of having many devices communicating wirelessly in our house, arguing that the signals have negative effects on our physical health.
I would like to tell them the ...
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Why isn't my calculation that we should be able to see the sun well beyond the observable universe valid?
I recently read an interesting article that states that a human being can perceive a flash of as few as 5 or so photons, and the human eye itself can perceive even a single photon. The brain will ...
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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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What's the physics behind XKCD #2027 (time between lightning flash and radio wave burst)?
XKCD usually has solid (and often contemporary) science behind it. Lightning Difference, #2027 one says:
Q: What’s that trick for telling how many miles away lightning is?
A: Just count the seconds ...
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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 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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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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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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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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Cyclist's electrical tingling under power lines
It's been happening to me for years. I finally decided to ask users who are better with "practical physics" when I was told that my experience – that I am going to describe momentarily – prove that I ...
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Why doesn't light affect a compass?
In our daily life a lot of photons of visible light, infrared and radio etc move around us. We know that light is an electromagnetic radiation. So why doesn't that electromagnetic radiation affect a ...
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Do rainbows have ultraviolet bands and infrared bands?
We have seen that rainbows looks so colorful as we are only able to see only the visible light. But Do they also have ultraviolet bands and infra-red bands, that we are unable to see?
I know someone ...
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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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Can I use an antenna as a light source?
Can I use a normal metal antenna to emit visible light?
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Are there any theoretical limits on the energy of a photon?
Is there any lower or upper limit on the energy of a photon? i.e. does the mathematical framework we currently use to study photons blow up when a photon surpasses a certain upper limit of energy? (or ...
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