Waves are disturbances that propagate through space and time. Classically, they travelled through a medium, disturbing the particles but not changing their mean position. Electromagnetic waves/particle-waves need no medium; they are disturbances in their respective fields.

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Definition of a normal mode?

What is the formal definition of a normal mode for a string? And how does this relate to the definition from e.g. wiki that seem to be applied to discrete systmes of particles only? Also on a string ...
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Why do we lose signal in elevators? [duplicate]

Whenever I am talking on my phone and walk into the elevator the call drops as soon as the doors close, and also the WiFi signal completely stops. Why does this happen? Note: I am asking this ...
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Sound waves during day and night

A man stands on the ground at a fixed distance from a siren which emits sound of fixed amplitude . The man hears the sound to be louder on a clear day than on a clear night. Why?
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31 views

Why do dispersive waves get wider?

Consider the two waves $$y_1=Acos(\omega_1 t+k_1 x), \tag{1}$$ $$y_2=Acos(\omega_2 t+k_2 x), \tag{2}$$ where $\omega_i=k_iv(k_i)$ for $i=1,2$ so we have a dispersive medium. Then if we take their ...
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33 views

Is difference in wave number always small?

Over the last few days I have been looking at a derivation of group velocity. The derivation is the one shown in this question Deriving group velocity. I have seen this derivation in many places, and ...
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Why do objects have resonance at natural frequency?

What actually is a natural frequency for an object and what makes it vibrate with increased amplitude when coupled with an external oscillator that matches the natural frequency?
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66 views

Derivation of group velocity?

In the standard simplified derivation of group velocity (which can be found here) we use two waves $$y_1=A\sin(K_1x-\omega_1 t)$$ $$y_2=A\sin(K_2x-\omega_2 t)$$ In the proof we then get ...
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104 views

What happens to the velocity distribution during constructive interference?

Two pulses(one inverted & having velocity in the opposite direction) moving towards each other with same wavelength & amplitude after undergoing destructive interference do reapper. Why? ...
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510 views

Why can't transverse waves travel through a liquid?

Can someone explain why a longitude wave can pass through the liquid, but a transverse wave can't. And can someone recommend some good animation of these processes.
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41 views

Why doesn't the speed of the wind have an effect on the apparent frequency?

A boy is standing in front of stationary train. The train blows a horn of $400Hz$ frequency . If the wind is blowing from train to boy at speed at $30m/s$, the apparent frequency of sound heard by the ...
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76 views

Mathematical defintion of a standing wave? [closed]

I know that a standing wave is the superposition of two waves of equal amplitude and wavelength, moving in opposite directions. But I am looking for a more mathematical defintion of such a wave. The ...
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119 views

Energy of a wave and Planck formula

Especially from this post I understand that the energy of a wave is directly proportional to the amplitude of that wave squared. Therefore, we can determine the total energy of a wave by summing the ...
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1answer
66 views

Why is it mandatory to make the string taut/stretched for sending pulse/wave?

In order to send a pulse and to propagate it, the string must be under tension.$^\text{1}$ Why is the tension necessary? Why should the string be stretched/taut for the transmission of the pulse? ...
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Fresnel equations of S and T waves and Isofrequecy Curves: Feeling confused

First of all sorry for my (probably) bad english. I've been studying propagation of light in anisotropic media from the Born and Wolf and from Landau "electrodynamics in continuous media" and I'm ...
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30 views

Will a longitudinal wave propagate “forever” in a tube?

I understand that the wave will lose energy due to "friction" between the, lets say, water molecules, but in my mind at least the biggest loss of energy in a wave is normally the dispersion of it. ...
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1answer
121 views

What sort of waves are produced by tuning forks?is it transverse, longitudinal or both?

We often know tuning forks are used to to produce wave in various experiments that we do in lab. but the matter of concern is what sort of waves are produced by it? is it transverse, longitudinal or ...
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66 views

Mechanism of propagation of pulse in a string

If you give one end of a stretched string a single up-and-down jerk, a wave in the form of a single pulse travels along the string. This pulse & its motion can occur because the string is under ...
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21 views

Equivalency of Q Factor Definitions

The Q factor is defined (seemingly) as $$Q=2\pi\frac{\mathrm{energy \, \, stored}}{\mathrm{energy \, \,dissipated \, \, per \, \, cycle}}$$ however on Wikipedia is says that the Q factor can be ...
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50 views

In Young's double slit experiment how can we determine the shape of fringes formed?

Does the shape of fringe change if the type of source is changed (point source or extended source) or if the relative position of slits is changed (both lie on a line either horizontal or vertical to ...
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Non-linearity of a guitar pickup

I basically understand induction and why a pickup generates a signal. (From: http://www.brighthubengineering.com/consumer-appliances-electronics/64277-the-physics-behind-the-electric-guitar/) What ...
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Can light emit light?

How and why does the Huygens principle really work? I mean, does it always work? The Huygens principle: Every point on a wave-front may be considered a source of secondary spherical wavelets ...
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112 views

Field Vectors and satisfying Maxwell's equations

If I have an electric field that its direction is parallel to the direction of the wave propagation, it will not satisfy Gauss's law for vacuum. However we can say it satisfies Gauss's law for ...
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1answer
21 views

Why do circular “snowrafts” form on a lake during a blizzard?

I was just out walking along Lake Michigan during a snowstorm and I noticed that the snow was clumping into these interesting circular "snowrafts". They all seem to be about 6 to 10 feet across with a ...
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113 views

Diffraction grating problem [closed]

We have 8 slits, each separated from its neighbour by $ 0.05$mm. We use light of wavelength $576$nm. The problem is to calculate at what angle the first minimum occurs. The answer is given: ...
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91 views

What is a full cycle in damped oscillation?

Maybe it seems a dumb question, but I can't understand what the cycle in a damped oscillation is? Let's take an example: In harmonic motion, one cycle is the smallest distinguishable part of wave ...
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94 views

Why is beat described as a “relatively slow amplitude-modulation of oscillation”?

Excerpts from A.P.French's Vibrations & Waves: . . . It may be seen that the combined displacement can be fitted within an envelope defined by the pair of equations$$ x = 2\mathit{A} ...
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187 views

Natural Frequency of an object and the phenomenon of resonance!

I have read about the term natural frequency in quite a lot of places. But I haven't found an explanation as to what is vibrating. It was pretty awkward when I couldn't clearly answer my little sister ...
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210 views

Huygens' Principle and Ocean Waves

Ocean waves can travel in any direction, but waves breaking on the sea-shore are usually approximately parallel to the line of the beach. How can Huygens' principle explain this phenomenon? Does it ...
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99 views

Longitudinal Waves - how velocity varies with density

The formula for finding the velocity of a longitudinal wave, such as a sound wave, is: $$v = \sqrt{\frac{E}{\rho}}$$ Where $v$ represents the velocity, $E$ represents the elasticity of the medium, and ...
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98 views

Confusion in understanding the concept of beats

. . .it is the combined vibration or disturbance basically having the average of the combining frequencies, but with an amplitude that varies periodically with time-one cycle of this variation ...
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51 views

In order for the occurence of beat, why is it compulsory that $|{\omega_2 - \omega_1}| \ll \omega_1 + \omega_2$?

As A.P.French in Vibrations and Waves writes, The beating effect is most easily analyzed if we consider the addition of two SHM's of equal amplitude: $$ \mathbf{x_1} = \mathrm{A} \cos{\omega_1 .t} ...
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96 views

Relation between sound waves and air molecules

The following was written in my book When sound waves travel in air, air molecules do not move. When wind blows,air molecules move. This produces variation in velocity of sound waves. The first ...
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13 views

how to measure the wave emitted from some particles after input sine wave into the particle

which waves can be input into the particle? is it sine wave? is the wave emitted from the particle after input wave into the particle different? if want to measure the output wave, how to use math ...
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61 views

How much energy and momentum is carried by a mechanical wave?

Let's assume there is a wave spreading across in a substance. Described by some partial differential equation. How can I calculate the momentum and energy carried by this wave? Or maybe the energy and ...
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1answer
138 views

What is the advantage of using exponential function over trigonometric function in analyzing waves?

A.P.French in his book Vibrations and Waves writes: . . . Why should the exponential function be such an important contribution to the analysis of vibrations? The prime reason is the special ...
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80 views

Physical intuition for the solutions of the wave equation

I have been studying the wave equation in $\mathbb{R}^n$ for the cases $n=1,2$ and $3$. In the three cases, working all over $\mathbb{R}^n$. That is: $u_{tt}(x,t)=c^2 u(x,t)$ for $x \in ...
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26 views

Is the oscillation of all particles for stationary wave equal?

Is the oscillation of all particles for stationary wave equal? I think the point of nodes for stationary wave never oscilliate. Is this idea true?
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1answer
236 views

Huygens' Principle During Reflection: comparing wavelets from before reflection with wavelets from during reflection

I was recently reviewing geometric optics, during which I read about Huygens' Principle and how it could be used to prove the Law of Reflection from the "light is a wave" viewpoint. I'll quote what I ...
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2answers
76 views

Does sound have a “louder” direction?

I have a question about the propagation of sound waves. We have two TV's in our house that are almost right on top of each other. One is located on the first floor and the other one is located on ...
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Acoustics - Phased Arrays

Has any work been done on phased arrays of speakers and microphones on the walls of a house being used to; * create maximas of ultrasonic waves at a given point in a room. * software to ...
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44 views

Besides vortex rings, are there other types of traveling waves that can carry matter as well as energy?

Vortex rings are a special soliton wave that are known to carry matter over a distance as well as energy. This can easily be demonstrated using a cardboard 'vortex canon' filled with smoke. The smoke ...
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126 views

What is the difference between real and imaginary parts of a sinusoid? [closed]

Can somebody explain, without using complicated mathematical formulas, what do real and imaginary parts of the sinus function represent? And what are relations between them? I cannot understand why ...
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51 views

Waves - determining whether a given formula represents a wave

Well the basic formula of a wave needs to contain $$y(x,t) = f(x \pm vt)$$ where the sign depends upon the direction of propagation of the wave. However, not every function in the form $y(x,t) = f(x ...
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128 views

What is the physical significance of the negative amplitude of a light wave?

I want to understand what is the physical significance of negative amplitude of a light wave? In an ac electrical circuit, I understand that negative amplitude signifies the amplitude measured when ...
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4answers
470 views

Surface waves on Dr. Miller's planet

In the movie 'Interstellar', the crew land on a water world orbiting a black hole. The gravity is greater than that of Earth and there are huge surface waves present in the ocean that they land in. ...
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17 views

Pressure evolution equation atmosphere

Working on gravito-acoustic wave propagation in a windy and viscous atmosphere I tried to recover the pressure evolution equation. My starting point was the adiabatic state equation : ...
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90 views

Wavefront of a wave?

I'm trying to understand the idea behind a wavefront in a visual manner. Take a look at these surface waves in water Now imagine if I sliced it twice, through the origin, in a vertical plane. I'd get ...
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107 views

Why do these standing waves appear to be traveling?

Take a look at this video: https://www.youtube.com/watch?v=TKF6nFzpHBU You would expect guitar strings to produce standing waves, and in fact, the upper, thickest string does often produce long, ...
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274 views

Physics of guitar strings

Guitarists normally press down hard on the frets and then pluck a string to obtain a note. However, one can also create notes by just touching the string above a particular fret and plucking. For ...
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What is the wave propagated away from an impulsively excited spherical shell?

Consider a spherical shell of radius $R$ centered on the coordinate origin, and an impulsive excitation $\delta (t)$ distributed over its surface ('ie. a single layer'). Each point on the sphere’s ...