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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