# Tag Info

74

In general, red and blue light do not travel at the same speed in a non-vacuum medium, so they have different refractive indices and are refracted by different amounts. This phenomena is known as dispersion.

72

But that still means the ear is only moving at one frequency at any given time No, it doesn't mean that at all. It means the eardrum is moving with a waveform that is a superposition of all the frequencies in the sound-wave it is receiving. Then, within the inner ear, hair cells detect the different frequencies separately. It is entirely possible for ...

59

Some areas of physics are counter-intuitive. For them, your everyday experience is a poor guide to how the universe really works. This is one of those areas. Photons have no mass. They all have the same speed. Yet they have energy and momentum, and it isn't the same for all photons. If you are used to $p = mv$, this doesn't make sense. The explanation is ...

48

Most computer monitors aren't capable of displaying any spectral color. Some of the RGB monitors could display at most three of them: some red wavelength, some green and some blue. This is because the gamut of the human vision is not triangular, instead it's curved and resembles a horseshoe: In the image above, the black curve represents the spectral colors,...

28

An capacitor has one intuitive property: Its voltage can't change instantly since its voltage is dependent on the charge it has stored, and charge doesn't move at infinite speeds (there is always resistance somewhere), therefore you can't instantly charge up a capacitor without infinite current. More capacitance means less voltage for the same amount of ...

24

Let me add something to anna v's answer. The classical model of blackbody radiation is based on: an exact recasting of the Maxwell equations describing electromagnetic radiation in a cavity, which shows that this physical system can be described as an infinite set of classical harmonic oscillators (normal modes) whose frequencies start from zero and are not ...

19

A photon cannot lose all of its energy by Compton scattering, as that would violate conservation of four-momentum. Imagine a photon with four-momentum $(p,\vec p)$ gives all of its energy (and thus all its momentum) to an electron with four-momentum $(m,0)$, in $c=1$ units. Then by conservation of four-momentum, the new four-momentum of the electron would be ...

18

Frequency. As you mentioned, wavelength changes in different mediums, but frequency doesn’t. If you look at a red ball underwater, it still looks red, even though the wavelength of the light is quite different.

17

They differ in their energy. Special relativity states that $E=\sqrt{m^2c^4 + p^2c^2}$. For a massive particle, there is a one on one relation between its energy and speed. In the limit $m \rightarrow 0$ this is no longer the case. All massless particles move at light speed, but their energy/momentum can vary.

17

If you're really curious, buy a cheap prism, and take it outside in sunlight. You'll be dispersing the frequencies present in sunlight, and in addition, your eyes are more or less sensitive depending on the frequency, but that's a good start for being able to see what a "real spectrum" of visible light is. A monitor does not produce all frequencies ...

15

If the wave is truly monochromatic then it will be sinusoidal. If it has a different profile then Fourier's theorem tells us that it can be built from an infinite series of (co)sine waves with increasing integer harmonics of the principle frequency (i.e. not monochromatic).

14

The only difference between the two is the energy they have. $$E=\frac{hc}{\lambda}$$ As you can see from the equation above, different energies means different wavelengths. Different wavelengths means different colors. It is important to know that even though photons are always massless and always move with the speed of light, that does not mean that ...

14

The refractive index is a function of wavelength. It has different values for different wavelengths. The way to show this in the mathematical notation is to write $$n(\lambda)$$ just as you would write $f(x)$ for some function of $x$. So with this more complete notation Snell's law is written $$n_1(\lambda_1) \sin (\theta_1) = n_2(\lambda_2) \sin (\... 14 the human ear separates out and detects all the frequencies within its range individually (in parallel) in real time, and sends that decomposition to the brain along a bundle of nerves. The eardrum responds to the instantaneous sum of all the different frequencies impinging upon it. That complex amplitude sum looks like a crazy squiggle which moves the ... 14 Given any photon, there is a frame of reference where it has any energy you like. Arbitrarily high or low. There may be a wavelength so long and an energy so low that you cannot detect it. But it is still a photon. If it has an arbitrarily low energy and momentum and it scatters off a particle at rest in your frame, it will not deflect the particle very much.... 11 This link clearly shows the classical and quantum derivations Blackbody radiation" or "cavity radiation" refers to an object or system which absorbs all radiation incident upon it and re-radiates energy which is characteristic of this radiating system only, not dependent upon the type of radiation which is incident upon it. The radiated ... 10 What is the physical behaviour which allows a capacitor to act as a high or low pass filter? A capacitor alone cannot act as either. To create a filter you need a combination of resistance and capacitance or inductance and capacitance (or RL). You need two immittances, at least one of which is reactive. Let's take a practical example, an RC circuit. This ... 9 Imagine electricity as water in a pipe. The current can flow in either direction (direct current, DC) or one way then the other way (alternating current, AC). Now put a rubber membrane in the pipe. This is the capacitor. Now it will slow and then stop DC, but AC can still keep wobbling back and forth. In this way, capacitors block DC but enable AC. ... 9 It may help your thinking to distinguish the term "photon" from the term "light pulse". The concept "photon" comes from quantum physics, and it refers to the degree of excitation of of the electromagnetic field at some given frequency. This means that a photon cannot change frequency, by definition. But in a process such as ... 8 When you look at images on your computer, you’re seeing light emitted from the LEDs (most likely) in the pixels of your screen. Those pixels generate colors by combining the output of LEDs with only a few different center wavelengths. Want purple? Mix blue and red. Want a slightly different purple? Adjust the proportions of blue and red. Your eyes and brain ... 7 Your interpretations all make two basic mistakes. You assume the recorded data was mathematically accurate, and the FFT algorithm used somehow produces "exact" results. Some of the "broad spectrum" at low frequencies is most likely just environmental background noise. The signal to noise ratio compared with the peak amplitude is around 40 ... 7 Sometimes for physical intuition, it's nice to think about the extreme cases. For instance, a zero frequency signal is just a DC voltage. If we send it through the RC high pass filter, the capacitor is just like a break in the circuit, and prevents any current from flowing. Slightly more quantitatively, the capacitor equation Q = CV implies that if we ... 7 Others already pointed out the effects of sensors and pigments (or emitters) that cannot perfectly mimic the response of the (standard) human eye. So one would need to look at a real spectrum. The excellent answer by Jonathan Jeffrey is to point to a prism. But there one has the problem that the dispersion increases towards the ultraviolet, and that relative ... 6 If you are asking about detectable gravitational waves - for example the black-hole/black-hole merger signals as detected by LIGO, then typical frequency (tens to hundreds of Hz) is in the audible range. If you are asking about gravitational waves in general, then there can be vibrations at any frequency at which two masses can move relative to each other. ... 6 Other answers are saying it's frequency alone. That is not true. Frequency does, however, play the biggest role in perception of color. Especially when neglecting edge cases like humans hardly perceiving any color in low-light conditions due to cones being less light-sensitive than rods. Rods only support monochrome vision (brightness only; no color). ... 6 In general relativity, any test particle's worldline (whether the particle is massive or massless) is determined entirely by its initial four-velocity u^\mu, and not by any other properties. This is manifested by the geodesic equation$$ \frac{d u^\mu}{d\tau} = \Gamma^{\mu} {}_{\rho \sigma} u^\rho u^\sigma. $$From the properties of ordinary differential ... 6 So too much frequency and you do lose the ability to decipher it and it starts to just sound like nosie? If that happens, it's because of how your brain interprets the signals that it receives from your ears, and not because of the physics of how your ears work. If the total sound pressure level is not so great as to damage your hearing, then your ears will ... 6 What happens to a photon when it loses all its energy? A photon is by definition a quantum mechanical particle of mass zero, spin one, and energy equal to hν where ν is the frequency of the classical electromagnetic wave that a lot of photons of that energy will build up. It follows special relativity rules, i.e. it is described by a four-vector and ... 6 Well, the wave equation is$$ \frac{\partial^2 u}{\partial t^2} = c^2 \frac{\partial^2 u}{\partial x^2} $$where c is just a constant, and has the interpretation of wave velocity (by simple dimensional analysis). Putting in u(t, x) = e^{i(\omega t−kx)}:$$ \frac{\partial^2}{\partial t^2} e^{i(\omega t−kx)} = c^2 \frac{\partial^2}{\partial x^2}e^{i(\...

5

A plane wave is a single frequency , a sinusoidal variation in space and time by mathematical construction. Mathematically : the traveling wave solution to the wave equation ... is valid for any values of the wave parameters, and since any superposition of solutions is also a solution, then one can construct a wave packet solution as a sum of ...

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