# Tag Info

## New answers tagged waves

0

The phase of a sinusoidal wave is represented as: $$y(x, t) = a \times \sin(\omega t + \phi)$$ So the time evolution (i.e the part that changes with $t$) is only the $\omega t$ term and not the pure constant phase $\phi$ term. $\phi$ can depend on $x$ or other things but not $t$. This is what is meant that the phase is constant. In case you mean sth ...

0

Even though the forces started at different times, is there any displacement of the metal box in any of the situations? Or is there any movement at all but is the net displacement zero? Sure. If you think of each force as causing an acceleration, the first one begins an acceleration in one direction, the second an acceleration in the other (or a ...

0

Imagine you standing some distance from me, and you move a charge back and forth along the line joining us. Waldir, you are quite right that the electric field I observe will fluctuate, and that these fluctuations will not reach me instantly - they will travel at the speed of light. However, this is not electromagnetic radiation. Why?- The electric field ...

0

Electrical amplification is about using an input signal to modulate a larger amount of power that comes from a separate power supply of some sort. And yes, there is such a thing as a magnetic amplifier that works on a very similar principle (even though the inputs and outputs are usually electrical). But you can't get an output value that's greater than the ...

2

There are several ways to amplify the magnetic field, though the mechanism is not same as for electrical signal amplification, but still they are fruitful. compression:- since a magnetic flux through a surface remains conserved, if we compress the field lines or stretch (or fold) the field line then we can increase the energy by working against the field ...

0

In QM the Schrödinger equation, is the equivalent of Newton's law in Classical Mechanics. The Schrödinger equation describes the state of a quantum system (i.e. atoms, subatomic particles etc.), and how the quantum system changes over time. I think you are getting confused because there are two main places where the term wave appears. (1) The Double Slit ...

1

"Bright light can never hurt your eyes" seems false to me… enough energy focused on the retina will cause damage, regardless of the wavelength. Otherwise you would not need to wear laser goggles… That aside, materials typically have certain ranges where they absorb light more strongly than others. There is no hard and fast rule for this, but if you google ...

0

Uv goes thru glass, I thought that comment strange when I watched it. Laminated glass (which it could have been) would shield about 95% of the uv, I believe due to the resin interlayer.

2

The following picture (from http://hyperphysics.phy-astr.gsu.edu/hbase/waves/imgwav/circonwave.gif) gives you a better sense of how to reconcile your observation with "circular motion": As you can see - there is circular motion for particles at the surface: they don't have to go under water to do it though. Incidentally this also shows that in the trough ...

0

Imagine the horn has a variable speed $v(t)$ relatively to the observer, the position of the horn relatively to the observer is given by $x(t)=\int_0^t v(u) du$, supposing $x(0)=0$ Suppose we are interested only at the (periodic) maximums of the sound, corresponding to a period of the emitted sound, at $t_0$, $t_1=t_0 + T$, where $T$ is the sound period, ...

2

The question, answers and explanation are poorly worded. Since the observer's velocity changes, the nature of that change, his/her acceleration, is significant. If the observer begins to accelerate away from the source, and continues to accelerate, then the perceived frequency will continue to decrease (as long as the observer stays sub-sonic!) At any ...

2

If the observer moves away with a constant velocity, they will hear a different frequency, but $f'$ will remain the same. Perhaps the problem meant that the observer accelerated away, or it is possible that the textbook editors made a mistake (which happens more frequently than most people realize). As for your second question - if the observer ...

1

The energy flux of an acoustic wave is $$\vec J = \vec v p \;\;\;\;\;\;\;\;\;\;\;\;\; (1)$$ The relevant energy density to be used in these calculation is actually $p+1/2 \rho v^2$, but since we are discussing a small amplitude wave (= no shock wave), $v$ is an infinitesimal quantity; thus $1/2\rho v^2$ is lower order than $p$ (second vs. first), thus it ...

-1

Let's start with what should be easy to determine: By convention, the second lens clearly has a negative focal length That's about it. The rest we need to assume. (A) is clearly not true. There is no scenario that allows this to happen. (B) must be true except in the trivial case where the negative lens is at the focal point of the first lens. That ...

0

There is one limit in which this computation is easy to do. Let us consider a massive, perfectly rigid ball striking a a perfectly rigid floor. In this case, there is nothing oscillating, so that we can neglect sound generation by oscillations in the ball or in the floor. Yet there will be sound, because the ball displaces air in its fall, and the air ...

1

The confusion you face is a historical one. Originally the interactions of different bodies was thought to happen at a distance more or less instantly, such as the case in the time of Newton and his gravitational theory. But when we discovered electromagnetism, and in particular, when Maxwell completed his formulation of Electromagnetism as contained in ...

3

A wavefront (your signal) has a fixed amount of energy given to it by the transmitter. Whatever happens to the wave once it leaves the transmitter is independent of the transmitter, thus receiving a signal does not drain any additional energy from the transmitter (though it can drain energy from the wavefront itself). EDIT: As pointed out by @Alfred ...

8

A wave can propagate in any medium that is: a) elastic b) less than critically damped Neither homogeneity nor isotropy are necessary. Any elastic system will return to it's original state when deformed, the question is just whether the deformation can propagate, and this is down to how quickly the energy of the deformation is dissipated. If the damping ...

4

A wave is generated by a disturbance in a medium. For a wave to propagate, do not necessarily need a medium. For example, an electromagnetic wave can propagate in vacuum, while a sound wave requires an elastic medium to travel. The requirements for the propagation of a wave, are dependent on the nature of the wave.

0

There is no such thing as “conduction of electric wave in conductor” (and I am unsure about where “electric waves” can be observed). There is a conduction of electric current in a conductor. One can say that electric potential in a piece of conductor is always the same (so the electric field is zero inside it), although it is not always so due to resistance, ...

1

The continuous stream of air that you are blowing in, it doesn't enter the pipe continuously. When the stream of air hits the hard edge in an organ pipe, it flaps in and out of it due to the difference in the density of the air outside and inside the pipe. This oscillation of the air in and out, it will be a periodic energy supply for the standing wave in ...

4

The trouble is that your table, or whatever object it is, will act as a waveguide. That's because the sound waves will (partially) reflect of the wood/air surface then travel back into the table and interfere with other waves. The result is going to be hideously complicated to calculate. As Luboš says in a comment, if the thickness of the table is much less ...

5

Yes. Higher frequencies are attenuated more over distance than lower frequencies are, which has a rounding effect on the square wave as the upper harmonics are reduced. Reference Do low frequency sounds really carry longer distances?

1

There is a good explanation of this in Matter and Interactions vol II by Sherwood and Chabay. I no longer have the text; I will try to summarize its explanation as I remember it. The electrons in a substance are analogous to charged masses on springs. The electrons in insulators are relatively tightly bound; those in conductors are loosely bound or unbound. ...

3

An overview in layman's terms: First, it is important to note that not any electric field will induce current in a conductor, because other than the fact the intensity of the field defines the speed of each charge (bigger difference of potential), the oscillation frequency of the $\mathbf{E}$ also plays a very important role, if the frequency is too high, ...

8

The reasoning has to be the other way around: Light acts on the metal and makes the electrons move. This, however, results in an energy loss, as the electrons feel a resistance and thus the radiation loses energy. This can be formulated more precisely with counteracting electric fields. That's why all good conductors are opaque. In insulators this can not ...

59

Since cables carry electricity moving at the speed of light, why aren't computer networks much faster? Perhaps I can address your confusion with a rhetorical question: Since air carries sound moving at the speed of sound, why can't I talk to you much faster? The speed of sound is much slower than light, but at 340 m/s in air, it's still pretty damn ...

0

You cannot compare pitch and colour as the latter is not biunivocally related to frequency but is often an elaboration of human mind. We see more colours than frequencies, comparing them is a gross simplification and may be misleading: (http://en.wikipedia.org/wiki/Opponent_process) (http://en.wikipedia.org/wiki/CIE_Color_space) @mateuz, I am not sure what ...

1

You're question is very broad, and will probably be closed, but recently, in researching my answer to this other question, I found what may in fact be the first documented instance of someone making an informed analogy between sound and light, namely Young in his lecture to the royal society in 1803 on his observations of interference of light. I'll ...

4

"Surely this is a bottleneck" - No, it's really not. Any real-life network connection is not speed-limited by the propagation speed of the signal in the cable, but by the processing delays in the various routers, switches, and network interface processing at each end.

2

Two reasons: 1) The speed of light in a "medium" is (almost*) always slower than the speed of light in a vacuum. 2) Electricity propagating in a wire is subject to inductive and capacitive effects which slow it's progress. And even if wires were infinitely fast, integrated circuits are not. Again, inductive (a little) and capacitive (a lot) effects limit ...

3

Why only 64% What does propagation speed mean? I know there are other variables effecting the latency and perceived speed of computer network connections, but surely this is a bottle neck. Speed of signal propagation is distance the signal (packet) travels in one second. It is usually lower than $c$ because EM waves that carry the information travel in ...

11

A transmission line is made of a pair of conductors which have some resistance, inductance, capacitance, and leakage conductance. We can take all of these per unit length: The wave equation for signals in this line, in the limit of a lossless cable with $R=0$, $G=0$, is $$\frac{\partial^2 V(x)}{\partial x^2} + \omega^2 LC \cdot V(x) = 0$$ You have to be ...

21

As you've probably guessed the speed of light isn't the limitation. Photons in a vacuum travel at the speed of light ($c_o$). Photons in anything else travel slower, like in your cable ($0.64c_o$). The amount the speed is reduced by depends on the material by the permittivity. Information itself is slower still. One photon doesn't carry much ...

0

The speed of electrons that flows in the cable, i.e. the current, is only a few m/s. The EM wave propagates much faster. Anyway, the speed of a computer no depends intrinsically of the speed of electrons, but the speed of energy transfers between electronics components.

3

How sure are you that electricity travels at the speed of light? Although electricity propagation moves at the speed of an E/M wave, and not electrons, its speed depends on the dielectric constant of the material. Only in a vacuum, I think, would it travel at the speed of light.

0

If you consider a mechanical wave in a string, that is possible as long as you keep $\omega A$ fixed. That is because the energy of a mechanical wave is given by $I = \frac{1}{2}\rho v\omega^2A^2$ Many textbooks would contain a proof, and http://cnx.org/content/m12793/latest/ may help as well.

7

You should look at the form of the advanced fundamental solution of D'Alembert equation, built up in geodesically convex open sets including the source localized at the event $y$ and the test point localized at the enent $x$ receiving the wave generating by the source. The construction, at least for analytic manifolds with analytic metrics, is obtained by ...

3

It generally does not work in curved spacetime. There is a quite thick book almost completely devoted to study this issue by P. Günther: Huygens' Principle and Hyperbolic Equations. Some discussions can be found in Friedlander's book about the wave equation in curved spacetime. A necessary condition for the validity of the Huygens principle is that the ...

0

It is possible for spacetime curvature to scatter and reflect light. The most obvious case of this is gravitational lensing. It's probably best to just solve the wave equation for the underlying light against the correct metric than to appeal to a simplifying principle like Huygen's principle.

1

For an electromagnetic wave, this is the propagation constant. It can be expressed as the sum of two terms: the attenuation constant and the phase constant.

1

Consider the initial pulse - it is of finite and short duration. It contains a number of frequency components, with higher and higher frequencies required for shorter and shorter initial pulses. This can be seen by taking the Fourier transform of your initial pulse. As the pulse propagates and the higher frequencies are preferentially absorbed, you can no ...

0

A crude overview: The flute's musical range extends up to three registers, starting from $B_3$. The way one switches between the registers is usually done in three ways: The blowing pressure The length of the air jet The area of the lip opening For example the most efficient way to increase the fundamental frequency is by extending the time for the air ...

1

The thing which is "vibrating" is the electromagnetic field, namely its $\vec E$ and $\vec B$ vectors. The animations here show precisely this. Of course, it's not that some particles vibrate in this case. The electromagnetic wave can exist without any matter at all — all it needs is the field, which is present everywhere. But, if we have some charges ...

1

For low-frequency radiation, it's quite simple: there's some electronic circuit that works (simple case) analogous to a tuning fork, but instead of building up mechanical tension it charges a capacitor and instead of the inertia in the fork's arms it has a magnetic field in a solenoid. You can measure the voltage against time, count the oscillations in one ...

0

Because when you take the sine of 0º to 360º and plot the graph of these values, AC current behaves the same way. It can also be represented by a cosine function, but in this case we assume that the initial value of the AC current shouldn't be zero.

1

The off-axis intensity is not sero, it is simply quite low. This article on the Wolfram web site shows the 2D diffraction pattern from the sort of aperture you describe along with the equation for calculating the intensity: $$I = 16C^2a^2b^2\left(\frac{\sin(\theta_xka)}{\theta_xka}\right)^2\left(\frac{\sin(\theta_yka)}{\theta_yka}\right)^2$$ where the ...

0

I will reply to this: why is then frequency defined for matter waves(in other words what is its use?)? Frequency is defined for electromagnetic waves. When the photon was discovered and the theory assigned to it an elementary particle identity, on par with electrons and protons (at the time ) it was found that the frequency of the electromagnetic wave ...

-3

I think that matter wave could be both longitudinal as well as transverse!!! Even if, by this time, any scientist anywhere proved that it is either longitudinal or transverse, may be corrected by somebody else in future with this change - it is both longitudinal as well as transverse. As we know generally, the concept of matter wave is just the idea of ...

Top 50 recent answers are included