# Tag Info

22

You don't. You actually hear the high frequency notes from headphones. The bass really doesn't travel at all well, but the attack noise from the drum or bass guitar is what leaks from headphones. This is why on the tube you hear "tsss tsss tsss tsss" and very little else. From @leftaroundabout's answer on the post that valerio92 linked: Normal ...

6

My high school physics teacher was saying that “this is because of interference of sound waves. During the day, there are a lot of sounds and they cancel each other due to interference. But, during the night, there are few sounds and they can reach to our ears without canceling each other”. You need a better high school physics teacher. Temperatures tend ...

6

Any physical phenomenon is potentially capable to cause some change to any other phenomenon, more or less directly. If it was not the case, the physical world could be divided into completely independent realms; there would not be the one single world we call Nature. Practically though, many if not most of the actually existing interactions between systems ...

6

Dispersion in waves arises from both material property variation with frequency and from the geometry of the fields in question. That wave dispersion will arise from material property variation is obvious. But wave geometry and boundary conditions also matter. Simple example: a conductive waveguide with rectangular cross-section with sidelengths $a$ and $b$...

5

In general the wavenumber is a vector. That is, $e^{i(\vec{k}\cdot\vec{x}-\omega t)}$ is a solution to the wave equation in 3 (or any number) dimensions. We say this solution is a plane wave propagating in the $\hat{k}$ direction with wavenumber $|\vec{k}|$ or wavelength $\lambda = 2\pi/|\vec{k}|$. So properly the de Broglie relation is $\vec{p} = \hbar \... 5 I can answer half your question in that a sound can change the path of light. A change in the density of the air produces a change in the refractive index of the air and so a Schlieren photograph can make this visible. Here is a YouTube video to show a sound wave produced by clapping. 4 They do cancel each other when the peaks of one coincide with the troughs of the other, but since they move in opposite directions, this only happens at specific moments in time (every half period). At other moments (one fourth period later), the peaks of both waves will coincide (and so will their troughs). In the figure above, the red and green wave move ... 4 Imagine something oscillating in space and time, for example a plane wave propagating across the axis$x$. This propagation is expressed via the so-called phase $$\phi(x,t)=\omega \cdot t - k\cdot x = \dfrac{2\pi}{T}\cdot t -\dfrac{2\pi}{\lambda}\cdot x \tag{01}$$ and the magnitude of the plane wave as $$E(x,t)=A\cos\phi(x,t) \tag{02}$$ As the ... 3 I would tend to agree that background noise is a factor, but rather than reducing, adding to the sound you are trying to make sense of. So part of that may be how your brain is able to filter the information from the background noise. But at night the temperature is lower and according to this tutorial on sound propagation (which does cite reliable ... 3 The classical interference pattern is explained by the equations governing the behavior of light, and energy there is treated as a collective phenomenon, using the Pointing vector Energy transfer in a light beam can be best understood as an emergent phenomenon from the underlying quantum mechanical level. Innumerable photons create the visible interference ... 3 To a very rough approximation we can say that frequencies of speech are selected by standing waves in the speakers mouth, larynx etc. If they breath helium the speed of these standing waves increases but their wave length, being constrained by dimensions of their body, remains the same. This results in higher frequency sounds produced. (think$f=v/\lambda$... 3 A wave is a solution of a wave equation of the form $$\frac{\partial^2\varphi}{\partial t^2}(x,t)=c^2\frac{\partial^2\varphi}{\partial x^2}(x,t),$$ where$\varphi$is the so-called wave function which represents some "displacement" from the equilibrium. The solutions of this equation are of the form$f(x\pm ct)$. This represents a traveling wave with speed$...

2

It is an expression describing a travelling wave. More precisely, it should say $$y(x,t) = A \cos (kx - \omega t)$$ where $x$ is the coordinate in space (location along a line in the direction where the wave is moving), $t$ is time, $k$ is $2\pi / \lambda$ where $\lambda$ is the wave length, and the Greek letter omega $\omega = 2\pi f$ is the angular ...

2

This is really just a geometry problem since we can not use Fraunhofer approximation in general. The solution depends on what you mean by "width" of the central maximum. If you take it to be the distance between the two adjacent minima (full width) then the solution is: $$z_{fresnel} = \frac{a^2}{4 \lambda} - \frac{\lambda}{4}$$ Alternatively the full ...

2

Based on Light Waves As I am sure you know, a photon (described in wave terms) has both oscillating electric and magnetic field (sine waves) at right angles to each other. Obviously then, if the electric field is drawn vertically , the magnetic oscillating field is drawn horizontal to it. The field always wants to reach a ground state of zero ...

2

Let's back up. How do you know that a monochromatic wave of frequency $\omega$ doesn't contain any component at $\sqrt{2} \omega$? It's because these two frequencies are not commensurate: if you plot $\sin(\omega t)$ and $\sin(\sqrt{2} \omega t)$ they'll have no clear relation. The peaks of one look like random points in the other. Then it's clear their ...

2

To say that a wave, say with amplitude given by f(t), has a period $T$ means that not only $f(t+T) = f(t)$, but also that $T$ is the smallest value that has this property. Given that $f(t+T) = f(t)$ then it follows that $f(t + nT) = f(T)$ where $n$ is an integer (for example $f(t+2T) = f(t+T+T) = f(t+T) = f(t)$).

2

The assumptions under the statement are that A. the oscillation count in a wave is conserved and B. the passage of time is universal and uniform. Since the frequency of a wave is the count of oscillations measured within a given time interval by a stationary observer, it remains the same anywhere the wave can reach. On the other hand, the wavelength is how ...

2

Keep in mind that frequency is both the wave property that is preserved in a change of medium (both wavelength and velocity change) and the physical property of sound waves that we experience as pitch. So the frequencies you hear in both cases are ones produced by the vocal cords. Nor do we expect the gas environment of the vocal cords to have a large ...

2

Yes, sound waves in a gas, liquid or solid can affect the light passing through it, as the motion of the atoms due to sound waves changes the atomic spacing, and this changes the index of refraction slightly. So the light would be diffracted and some amount of the light would experience a frequency shift up and a frequency shift down by the sound wave ...

2

Basically it is whatever you need to multiply a distance by to find a phase difference (in radians). For a traveling wave, the wave number is the amount of phase difference per unit length. For a physical sine wave, it is the ratio between the maximal slope of the wave surface and the amplitude. In other words, it measures how dramatic the local ...

2

In general, a mixed wave of the form $$f(x,t)=\cos(x-t)+r\cos(x+t)$$ will not have nodes, at least in the sense of points $x_0$ for which $f(x_0,t)\equiv 0$ for all times $t$. In general, there's relatively little to say beyond what the picture will convey: As you turn $r$ up from 0 to 1, you first start inducing modulations into the amplitude of the ...

1

Difference between real and absolute value in general: Look at count_to_10 's answer. For acoustics and preasure measurement: Absolute pressure - pressure against perfect vacuum. Real pressure: Usually defined as the pressure against a reference-environment. Also called differential pressure. For example the pressure of the air inside a football against the ...

1

The formula you cite contains all you need to answer your question. The following is the procedure used to assess the suitability of a link for many microwave communication links defined by many RF link planning standards, indeed pretty much any terrestrial radio link at any frequency these days, since we no longer depend on ionospheric reflexions (used by "...

1

For a travelling wave there is a phase difference between adjacent points in the medium. When two travelling waves superpose the resultant displacement of the medium is the vector sum of the displacements due to the individual travelling waves. At some points the two travelling waves arrive exactly in phase with one another and that is a position of ...

1

The sound wave is a property of the air, which does not care whether the object producing the sound was moving or not. Therefore in both cases the sound travels at the same velocity. That is the answer your book wanted, and while it is almost precisely correct, there is a slight complication. The point is that if an object in motion emits a sound which ...

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I'm not really sure that my answer fits with your request of a "uniform" background pressure gradient, but anyway it's a related subject. Have you considered perturbations of a fluid parcel in a hydrostatically balanced atmosphere? Conservation of momentum here relates the pressure gradient to the gravitational acceleration. It can be shown that perturbed ...

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I think the Rayleigh-Taylor instability may be considered to be amplified under a pressure gradient. Due to the difference in densities, there is a pressure gradient across the interface which becomes unstable after a certain time. The instability grows exponentially in time according to an amplitude on the order of: $$a\propto\exp\left(\sqrt{A}\right)$$ ...

1

Remember that the air at the closed end can't move, so the amplitude at that location is always zero: it is a node for the standing wave. The displacement or amplitude will be maximal at the speaker, it is an antinode. So the length of the pipe determines the wavelength. The distance between node and antinode of a wave is $\lambda/4$, so $l=\lambda/4$. The ...

1

A simple harmonic motion is one where the acceleration (or restoring force) is directly proportional to the displacement and in the opposite direction of the displacement. For a mass $m$ on a spring with spring constant $k$, the differential equation describing the motion becomes: $m\frac{\mathrm{d}^2 x}{\mathrm{d}t^2} = -kx$ That equation has as solution: ...

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