# Tagged Questions

Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.

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### Why do you get electric field of a light wave?

Why do you get electric field of a light wave in following form: $E(x,t)=A cos(kx-\omega t- \theta)$?( look at: https://public.me.com/ricktrebino -> OpticsI-02-Waves-Fields.ppt, p. 18)
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### Do ~1THz oscillators output “light”?

Upon looking at some radiation levels higher than Microwaves, I have come across "Terahertz radiation". According to the article, there are numerous ways to generate such radiation, and that brings ...
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### Equations governing mutual inductance and transformers

What are equations for voltage ratio (primary/secondary) of... the action of a transformer with a turn ratio (turns primary/turns secondary) of X/Y and a toroidal core of cross-sectional radius R ...
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### Can extraterrestials detect our messages?

We transmitted several messages to the space and listening to space for signs of intelligent life for years (SETI). Assuming they have at least the same technology we have, could they detect these ...
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### Superposition of electromagnetic waves

The superposition of two waves is given by $$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$ For sound waves, this ...
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As a father to a small child, I have often observed this phenomenon but have until i posted this question not found the vocabulary to Google for it. Can you explain what I am seeing? In a darkened ...
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### How does Newton's 2-prism experiment help to explain why light does not get dispersed into 7-colors in a parallel glass slab?

In a real parallel glass slide(with two prisms imagined to be touching each other to form a parallel glass slide), The ray of light should pass through the Z in between without any dispersion or ...
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A sticker on my microwave oven states its output effect to be $750\ \mathrm W$, which is $180$ calories per second. This means that heating $250\ \mathrm g$ of water by one degree Celsius would take $... 4answers 7k views ### Can anyone explain to me why light is not dispersed into a spectrum through a parallel glass slide, but only through a prism? The question pretty much sums up what I need to know. Why is it that light only gets dispersed into a spectrum when travelling through two non-parallel sides(like a prism) and not through something ... 1answer 434 views ### Why doesn't anomalous dispersion allow faster-than-light propagation? It seems that the phase velocity of light could be greater than$c$, if$\sqrt{\epsilon \mu} < 1/c$, i.e. for anomalous dispersion. Are there examples of such media? For diamagnetics it seems ... 3answers 3k views ### How to calculate gamma radiation shielding? A device emits 0.2 μSv/h of gamma rays. How thick does an aluminum sheet need to be to completely stop radiation from coming out ? What equation is to be used to calculate this ? 3answers 7k views ### In electromagnetic radiation, how do electrons actually “move”? I've always pictured EM radiation as a wave, in common drawings of radiation you would see it as a wave beam and that had clouded my understanding recently. Illustration on the simplest level: ... 2answers 844 views ### Microwave oven + water: dielectric heating or ion drag? When you place a water or food in a microwave oven, it heats. Which process commits more energy to that: dielectric heating, or ion drag i.e. resistive heating? AFAIK, in distilled water (which is a ... 2answers 3k views ### Why is light described by a null geodesic? I'm trying to wrap my head around how geodesics describe trajectories at the moment. I get that for events to be causally connected, they must be connected by a timelike curve, so free objects must ... 2answers 70 views ### Does the efficiency of radiation change in any way in the presence of a medium? I've read that radiation doesn't really require a medium. But if you're taking, for example, the sun's light, then does its efficiency of transmission increase or decrease once it reaches the earth's ... 2answers 2k views ### Are Colors Emitted at Specific Temperatures? There are quite a few nagging questions I have been having over the years, I do not require a full explanation, just some guidance in my assumptions and pointers if I am very wrong. My basic ... 2answers 218 views ### References for Radio Imaging? I'm really intrigued by a bunch of questions like 'what do radio waves look like?' 'how much RF radiation is there in the town I live in?' 'how specifically does RF imaging work?' But I think I need ... 3answers 507 views ### Where does the light of the Big Bang come from? I'm wondering whether the residual light of the Big Bang comes from one particular direction and what possibilities do we have to detect its position? 2answers 466 views ### About change in velocity of a light wave as it enters a different medium [closed]$\dfrac {sin\theta1}{sin\theta2}=\dfrac {v1}{v2}=\dfrac {n2}{n1}$I understand this equation, but what is the velocity of a light wave going through air and what is the velocity/change in velocity as ... 3answers 102k views ### 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? 4answers 8k views ### Why does change in speed of a wave make it refract? When a light wave enters a medium with a higher refractive index (e.g. from air to standard glass) and its speed decreases, why does that make it refract/bend? I understand that wavelength decreases ... 2answers 155 views ### How Safe Are Heat Ray Guns? Could a little meddling with the frequencies of the Heat Ray Gun beam result in frying crowds rather than dispersing them? 1answer 253 views ### How to stop a heat ray gun What material would be best suited to create a shield to protect from the new heat ray gun? 4answers 4k views ### Efficiencies of Coupling Light into a Fiber I am in AMO Physics and work a lot with optics. I just wanted to get an idea of what coupling efficiencies one "should" get in a "reasonable time"* by coupling light into a fiber using different ... 8answers 10k views ### Why no longitudinal electromagnetic waves? According to wikipedia and other sources, there are no longitudinal electromagnetic waves in free space. I'm wondering why not. Consider an oscillating charged particle as a source of EM waves. Say ... 2answers 6k views ### Microwaves vs Gas or Electric Coil heating of a water boiler in a typical household Wouldn't it be more energy efficient and or safe to use microwaves to heat our home's water boiler instead of using dangerous gas or hot electric coils that could catch other things on fire? I'm kinda ... 2answers 12k views ### Penetration versus Frequency I would like to know the relation between penetrating ability and the frequency of a wave. For example, gamma waves have high frequency and high penetrating power: intuitively I imagined this as ... 2answers 2k views ### Why does a microwave oven affect other electronic devices When I turn my microwave oven over the stove on, it will cause a motion sensor light in the hallway next to the kitchen to got off and on. This affect can be reproduced anytime. I did notice that ... 3answers 1k views ### Is it correct to say that electromagnetic waves does not require a medium? I can conceive of a particle existing in empty spacetime, but not a wave. A wave appears to me at least, to insist upon a medium for its very definition. I understand that the 19C physicists ... 5answers 3k views ### 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, ... 1answer 25 views ### Is there any site/place which gives access to astronomical signals acquired from space? I am an engineer and I'd like to know if there are any places which provide access to any kind of astronomical signals acquired from space using radio telescopes. 2answers 446 views ### Is the electron wave function defined during photon emission I have heard the term quantum leap to describe the (instantaneous?) transition from a higher energy orbital to a lower energy orbital. Yet, I understand that this transition time has now been ... 1answer 380 views ### Experimental proof of gravitational redshift of light Has the gravitational red shift been proven for electromagnetic waves only or also for a single photon? 2answers 696 views ### Does sending data down a fiber optic cable take longer if the cable is bent? Ok, so, my simplified understanding of fiber optics is that light is sent down the cable and it rebounds off the sides to end up at its destination. Which got me thinking, if it has to bounce more ... 1answer 694 views ### Polarization rotation: Jones Matrix that maps Horizontal to right circular I am looking at the Poincaré sphere and I am trying to compute a Jones matrix for a particular rotation. Specifically, I would like it to perform the following maps:$O :|H \rangle \rightarrow |R \...
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1-Why the antenna of the radio of cars is located outside the car and not inside? 2-If the answer to 1 is because that cars are like Faraday cages then how come my cell phone can receive signal ...
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### What is the electric field part of an EM wave? Radiation field or the induction field?

Look at this image: I wonder if the electric field is from the induction field from a vibrating electron or the radiation field? If it is from the radiation field, as I suppose, than can someone ...
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### Cerenkov light - a practical calculation

I need to calculate the approximate total amount of energy radiated, via Cerenkov, by a muon as it traverses $10\:\rm{cm}$ of quartz glass. Unfortunately I've spent so much time fiddling with ...
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### Light Rays that are Perfectly Parallel

I just heard this simple reasoning in a documentary film: Light rays from distant stars are perfectly parallel. This is pretty interesting thought. In nature, it is hard to find something really ...
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### How to determine directions of vectors of an electromagnetic wave

I did an exercise which probably is quite popular, in which you draw an electromagnetic wave and prove that it should propagate at the speed of light $1 \over \sqrt {\mu_0\epsilon_0}$ using Farday's ...
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### Electromagnetic wave reflection vs. light reflection

Related: x-ray interaction with atmosphere I know that electromagnetic waves of particular frequencies reflect from the ionosphere. And the light (which from one perspective is an electromagnetic ...
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### Does EM radiation (any, i.e. RF), or sound, radiate everywhere at once?

I am having trouble understanding electromagnetic radiation (or waves in general, be it EM or sound). If I have a 1 Watt speaker, is it infinitely divided and spread out so that everyone in every ...
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### Why is it necessary for an object to have a bigger size than the wavelength of light in order for us to see it?

I keep hearing this rule that an object must have a bigger size than the wavelength of light in order for us to see it, and though I don't have any professional relationship with physics, I want to ...
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### Can a photon be emitted with a wavelength > 299,792,458 meters, and would this violate c?

Just curious if the possibility exists (not necessarily spontaneously) for a photon with a wavelength greater than the distance component of c to be emitted, and would this inherently violate the ...
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### x-ray interaction with atmosphere

Why x-ray are stopped by atmosphere while they are more energetic than UV or IR? They certainly interact with atmosphere but I can't understand which phenomenon stop them.
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### Peaks on top of Bremsstrahlung

The following is a graph of the intensity of Bremsstrahlung generated by accelerating electrons to hit a target vs. its wavelength. I'm wondering what causes the additional peaks for high energies? ...
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### Understanding the diagrams of electromagnetic waves

I'm having trouble understanding the diagrams of elctromagnetic waves. I have no problem with any concept in classical mechanics, and I think this can be answered without any relativity (which I don'...
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### Why can't electromagnetic radiation from magnets be used for apparent perpetual motion?

If electromagnetic radiation represents a transfer of energy, then does a permanent magnet represent unlimited energy, and if so, why can't magnets be used for perpetual motion? Even if permanent ...