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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If both radio waves and gamma rays can travel through walls
and they are on opposite ends of the electromagnetic spectrum, then why can't light travel through walls which is right in the middle of the spectrum?
This question has already been asked here. ...
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Angular momentum and EM wave
Is there any sense in saying that circularly polarized EM waves have angular momentum?
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Could a bubble of photons make a spaceship massless? [closed]
I'm not sure how theoretically possible this is but my question is...
If we could somehow make a perfect bubble of photons (a massless bubble) and put a spaceship inside it, could it therefore ...
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Low frequency electromagnetic waves
Some frequencies of electromagnetic waves are used for transmission of information, like radiowaves, microwaves, light, but some are not..
What about low frequencies?
Perhaps low frequencies aren't ...
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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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What is the effect of polarization on diffraction by a narrow slit?
Consider the well known demonstration of diffraction by a narrowing slit.
(See for example the demonstration at the 30 minute mark of this lecture at MIT by Walter Lewin)
It is my (possibly mistaken) ...
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What type of electromagnetic wave can pass through silver or aluminium standard mirror?
I have been told (not sure if it is true), that mirror (and glass) do not allow to pass the electromagnetic signals of mobile signals.
but for a standard mirror what type of wave can pass through it?...
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How does a honeycomb grid affect the travel of light?
A light modifier that is commonly used in studio photography is a honeycomb grid.
It narrows the beam of light to a circle with soft edges, as it can be seen here:
My question is: how is this ...
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Can we transport energy over infinite distances through vacuum using light?
I know that light (or electromagnetic radiation in general) attenuates in intensity as the square of the distance it travels.
Why does it attenuate?
Are the photons being scattered by the medium ...
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Light bending by black holes
In the center of our milky way, it is assumed that a black hole exists with a mass of $\approx 4\times 10^6$ times our sun's mass. How much light bending (in degrees) would arise for stars that are in ...
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Why do car keys have longer range when held next to your head?
I first saw this on Top Gear, and assumed it was a load of rubbish, but today I tried it out and it actually works, if you walk away from the car continuously unlocking/locking it until it stops, and ...
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How is the speed of light calculated?
How is the speed of light calculated? My knowledge of physics is limited to how much I studied till high school. One way that comes to my mind is: if we throw light from one point to another (of known ...
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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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Low frequency electromagnetic waves in General Relativity
I am becoming familiar with the Geometric Optics approximation in General Relativity which (to summarise) says that EM waves follow null geodesics under the geometric optics approximation. In the ...
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What is the effect of ice on an antenna?
A local FM radio station transmitting at 89.3 MHz recently announced that it would be running at 50% power due to freezing weather and a forecast of ice accumulation, as "when ice is forecast ... it ...
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Light emitted by an object according to its temperature
According to this picture
the light emitted by an object depends on its temperature.
That makes perfect sense when we heat a metal. As its temperature raises we see it red at first, then orange, ...
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Electromagnetic fields vs electromagnetic radiation
As I understand, light is what is more generally called "electromagnetic radiation", right?
The energy radiated by a star, by an antenna, by a light bulb, by your cell phone, etc.. are all the same ...
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Cellphone RF radiation
First, what determines the strength of an RF signal?
Why is it said that a cellphones radiates more energy when the reception from signal tower is lower in strength.
Why is it said that RF gets ...
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Newton's rings: What causes the other rings?
This is from an experiment we did in physics class. We shone a sodium light at a convex lens on top of a sheet of glass - and this image was captured by a USB microscope. I know what causes the main ...
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Reconciling refraction with particle theory and wave theory
I have searched the web for good answers to why refraction occurs when light moves from one medium to another with different density. I have limited background in physics and want to know if there is ...
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Can one make an axial mode circularly polarized radio wave filter with purely conducting materials?
Can one construct a filter out of nothing but pure metal that will pass only right circular polarized radiation and reflect left circularly polarized radiation?
What would it look like? A helical ...
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Gauss vs $\rm mW/cm^2$: same thing?
A friend of mine is concerned about electromagnetic field negatively affecting their health and got a "DMF meter" to measure the field strength in their house in units of milliGauss. They ...
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What's the problem with solar energy?
What "breakthrough" from a theoretical point of view is needed for solar energy to become feasible energy alternative?
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Do mirrors increase the amount of light in a room?
So if you have a light bulb in a room, and you had a tool to measure the amount of light that's in the room, then let's assume the amount of light only caused by the bulb is "1"
If you place a mirror ...
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Impedance formula for an edge coupled differential stripline in an asymmetrical stackup?
I've been searching and have not been able to find a formula for calculating the impedance of differential lines on inner layers where the dielectric above and below it is not symmetrical. I've seen ...
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Properties of the photon: Electric and Magnetic field components
Consider an electromagnetic wave of frequency $\nu$ interacting with a stationary charge placed at point $x$. My question concerns the consistency of two equally valid quantum-mechanical descriptions ...
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How is electromagnetic wave variation distributed in space?
Imagine an electromagnetic wave (a monochromatic one for example). The electric field amplitude and its variations travel in the propagation direction.
So, if there really exists a propagation ...
Hernan Eche
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Magnetron limits
What are the practical limits on generated wavelength in a Magnetron?
We know that Magnetrons could be used efficiently for generating microwaves for water heating, or for radar applications, but ...
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Can light emitting diodes be used to generate UV wavelengths?
I don't know much about light-emitting diodes, but I imaging if you had a panel of RGB diodes you could produce any wavelength of color within the visible light spectrum. However, if I
also wanted to ...
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What happens to light after it enters an eye
What happens to the light [energy] after it enters an eye and hits the rods and cones? I presume the energy becomes electrical, and it must be near 100% perfect, else our eyes would heat up? Or am I ...
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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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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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Electromagnetic weapons: power?
I essentially have three questions concerning weapons based on EM waves or more generally.
Focusing on the weapons using radio-waves and/or micro-waves, what power do these types of weapons need to ...
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Can radio waves be formed into a pencil beam?
Laser beams are said to have high "spatial coherence". This means that the beam is highly concentrated even at long distances (low spread).
Can this be achieved with radio waves (much longer waves) ...
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How large is the smallest object that can be detected at a given wavelength?
What is the cross section of the smallest object that can be detected with say visible light ($\lambda$ ~380 - 750 nm) or X - band radar ($\lambda$ ~20 - 50 mm).
Does the object need to have one side ...
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Home experiments using wireless LAN or mobile phones about electromagnetism?
Are there any nice experiments using wireless LAN access points or routers or mobile phones to demonstrate physical features of electromagnetic fields, especially em-waves?
More precisely I am ...
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Creation of the Electromagnetic Spectrum [closed]
After seeing this image:
http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg
And reading this:
"The long wavelength limit is the size of the universe itself, while it is thought that the ...
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Light emission spectrum units
Do someone knows the units of the spectra provided here ? It seems obvious enough that it's said nowhere, but even Wikipedia and other sites are quite blurry on this point.
So, is it power ($W$), ...
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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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Wi-Fi in the presence of very strong magnets?
A friend of mine claims to have been able to surf the Internet without fuss on a Wi-Fi connection while performing NMR on samples he was analyzing. I would have thought the strong magnets needed for ...
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Why do lightbulbs continue to glow after the light is turned off?
I've noticed that whenever I turn the lamp off in my room at night, the lightbulb seems to continue to glow for a minute or so after that. It's not bright though; the only way I even notice it is if ...
Whitney
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Way to measure wavelength of infrared radiation?
I am wondering if there is a device for measuring wavelengths of things. As semiconductors emit infrared radiation and I would like to know what is the wavelength it is so I can check to see if its ...
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What’s the relationship between thermal radiation and Johnson thermal noise?
All objects above absolute zero emit radiation due to random collisions between the atoms they are made of. The spectrum of radiation emitted varies according to the temperature of the object, I ...
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How can I determine transmission/reflection coefficients for light?
When light rays reflect off a boundary between two materials with different indices of refraction, a lot of the sources I've seen (recently) don't discuss the relation between the amplitude (or ...
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Is it possible that all neutron stars are actually pulsars?
I'm assuming that what I've been told is true:
We can only detect pulsars if their beams of electromagnetic radiation is directed towards Earth.
That pulsars are the same as neutron stars, only that ...
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What causes polarised materials to change colour under stress?
Our physics teacher showed the class a really interesting demonstration. He used two polarised filters in opposite orientations, then he took some antistatic tape and stretched it under the two plates....
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