# Tagged Questions

The wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats, and the inverse of the spatial frequency or wavenumber. Determined by considering the distance between consecutive corresponding points of the same phase, such as crests. Use for ...

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### What determines color — wavelength or frequency?

What determines the color of light -- is it the wavelength of the light or the frequency? (i.e. If you put light through a medium other than air, in order to keep its color the same, which one would ...
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?
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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: ...
382 views

### How is wavelength actually related to space (/distance)?

Is a photon of 400nm in wavelength "smaller" than a photon of 1km in wavelegth?
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### Why is air invisible?

I think that something is invisible if it's isolated particles are smaller than the wavelength of visible light. Is this correct? Why is air invisible? What about other gases and fumes which are ...
11k views

### Frequency of the sound when blowing in a bottle

I'm sure you have tried sometime to make a sound by blowing in an empty bottle. Of course, the tone/frequency of the sound modifies if the bottle changes its shape, volume, etc. I am interested in ...
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### Why do we think of light as a wave?

I've read that light travels in a straight line and has a wavelength of 400nm to 700nm. But I don't understand why does it have a wavelength and what creates its wavelength? I agree with the concept ...
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### Wavelength-dependent refractive index

I read in a book about optical fibers that the different spectral components of a light pulse transmitted in the fiber propagate with different velocities due to a wavelength dependent refractive ...
7k views

### How to measure the wavelength of a laser pointer?

I'm working on something and I need to know the wavelength of the laser pointer that I'm using. Can you suggest me a way, using some optics formulae, or anything else to calculate the wavelength?
3k views

### 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 for Quantum Mechanics blow up when a photon surpasses a certain upper limit of energy?...
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### Radio antennas that are much shorter than the wavelength

From my limited experience with ham radio when I was a kid, I expect transmitting and receiving antennas to have lengths that are on the same order of magnitude as the wavelength, and in fact I recall ...
3k views

### Is speed of sound really constant?

Does not speed of sound actually depend on the frequency and/or amplitude of the waves? If so, why it is constant?
135 views

### What is a wavelength of an EM wave physically?

This might be a silly question given I am a physics undergrad, but I was suddenly confused. Usually when EM hit a gap they diffract through the gap. But if the gap is too small, diffraction can't take ...
897 views

### Does the wavelength always decrease in a medium?

I was studying a GRE Physics Test problem where optical light with a wavelength of 500 nm travels through a gas with refractive index $n$. If we look at the equations for wave motion and index ...
83k views

### 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: ...
28k views

### Why is Near Field Communication (NFC) range limited to about 20cm?

Near Field Communication (NFC) operates at 13.56 MHz. Near Field is the region situated at a distance r << λ λ = c/f ...
5k views

### 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 ...
2k views

### Is the de Broglie wavelength of a photon equal to the EM wavelength of the radiation?

Is the de Broglie (matter) wavelength $\lambda=\frac{h}{p}$ of a photon equal to the electromagnetic wavelength of the radiation? I guess yes, but how come that photons have both a matter wave and an ...
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### What is the reason behind why a quantum particle cannot be at rest?

So I've seen different reasonings for this; which is correct, or are they both corollaries of each other? 1) For a particle to be at rest, we would know its momentum and therefore by Heisenberg's ...
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: ...
256 views

### Is the number of wavelengths of light spanning a distance invariant with respect to spacetime distortion?

I was recently asked by a friend how the expansion of spacetime affects photons. I gave him what I feel is a satisfactory general response, but it got me wondering how, exactly to calculate this ...
437 views

### Where does de Broglie wavelength $\lambda=h/p$ for massive particles come from?

I'm curious where the de Broglie relation $p=\frac{h}{\lambda}$ comes from? I know that for light (which has no rest mass), the following is true: $E=pc$ and $E=hf$ so, pc=hf \Rightarrow p=\...
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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, ...
600 views

### Why does light bend?

I have just read about dispersion of light by a prism and the thing which i donnot understand is that WHY does the light bend at all? Through prisms and slabs? I came to know that red light has the ...
2k views

### Matter waves and de Broglie wave length

The wavelength of a particle of momentum p is calculated using De Broglie relation. The de Broglie relation was postulated for what is called a matter waves. Now according to the statistical ...
97 views

### What is meant by infinite wavelength?

1#When an electromagnetic wave propagates in a plasma, with increase in plasma density the phase velocity ($v=\frac{\omega}{k}$) of wave increases. So at cut-off point $k=0$, and phase velocity ...
2k views

### Is the frequency of light restricted?

What are the factors that limit the frequency of light? Can it have wavelengths ranging between zero and infinity?
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### Why does Planck's law for black body radiation have that bell-like shape?

I'm trying to understand Planck's law for the black body radiation, and it states that a black body at a certain temperature will have a maximum intensity for the emission at a certain wavelength, and ...
177 views

### Is sunlight truly white?

I recently purchased a book on nuclear astrophysics, with no goal of mastering the topic but merely to read in between exams and hopefully learn something, it is revealed that the sun is composed ...
87 views

### Diffraction wavelength relationship [closed]

This question appears somewhat similar to other questions asking about why wavelength affects diffraction (a concept which I'm still not 100% sure on...) however my query is different and not answered ...
104 views

### Why do we perceive a colour?

White/yellow light hits a red case, and the red color is reflected into our eyes, since other wavelengths are absorbed. My question is: since both the paint on the case and the white light have ...
2k views

### 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....
255 views

### If photons don't “experience” time, how do they account for their gradual change in wavelength?

It is often said that photons do not experience time. From what I've read, this is because that when travelling at the speed of light, space is contracted to infinity, so while there is no time to ...
2k views

### Visible light spectrum to color space

I need to be able to convert an arbitrary emission spectrum in the visible spectrum range (i.e. for every wavelength between 380 and 780, I have a number between 0 and 1 that represents the "intensity"...
4k views

### Why do microwave ovens use radiation with such long wavelength?

According to Wikipedia: Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in). Typically, I put the dish inside the oven in its center. I suspect most ...
707 views

### Relation between wavelength and system size

We always say that when a given light wave interacts with atoms bound in a molecule, only waves with wavelength close to the inter-atomic-spacing are able to probe the system. In other context (...
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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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### Red color has largest wavelenght and violet minimum (in the range of visible light). then why does violet light appears reddish? RED + BLUE = VIOLET [duplicate]

My question is simple. Green light is more similar to red light than violet, then why is violet reddish and green not? in the language of frequencies and wavelengths, red and violet should contrast ...
364 views

### Physical meaning of wavelength of an EM wave

What is the physical meaning of the wavelength of light? This question has been asked before but I cannot find a satisfactory answer. Some respondents have said that the question is vague, I don't ...
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### Physical reality of calculated wavelength from the two measurable phenomena slit distance and fringes distance?

I see some difficulties in answering this question (Have we really measured the wavelength of light?) about the measurement of the light's wavelengths with double slit interference. "... we can find ...
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### Have we really measured the wavelength of light? [duplicate]

Have we practically measured the distances between the variations of electromagnetic radiations in space in nanometers or is it just theoritical because of calculations? Also the one who have marked ...
118 views

### Can speed of light be $c$ in air or other medium?

I know that the speed of light in a vacuum is $c\sim 3\ 10^8\ \mathrm{m/s}$, but I also know that speed of light in a medium (e.g., air) is less than that in vacuum. Special relativity says that ...