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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ratio between conduction current and displacement current

First, recall that Maxwell displacement current for a plane wave is $$ \vec j_D = \epsilon \partial_t \vec E = \epsilon \partial_t (\vec E_o cos(\vec k \cdot \vec r - \omega t)) = \epsilon \omega \...
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Why are electromagnetic waves called waves even though they don't travel through a medium?

If waves are defined as the oscillation of a medium, why are electromagnetic waves called waves as they do not need a medium to travel through?
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Natural frequencies

It's defined as the frequency that an object vibrates at when there is no driving force. What's a driving force? IS the natural frequency the frequency at which the atoms inside vibrate? People ...
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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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541 views

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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243 views

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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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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46 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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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 $$V_g=\frac{\...
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238 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 re-appear. Why? ...
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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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725 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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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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271 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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86 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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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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791 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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Do Photons Move in a Wave Like Pattern? [duplicate]

In many pieces of literature, light is said to travel like a "wave". Does this mean the light literally propagates through space like a wave as in up and down and so on or does light move linearly ...
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150 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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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 non-...
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28 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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258 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: $1.44\...
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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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236 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} \cos\...
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502 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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687 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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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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143 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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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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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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323 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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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: $u_{tt}(x,t)=c^2 \Delta_{x} u(x,t)$ for $x \in ...
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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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2answers
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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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3answers
139 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 the ...
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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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404 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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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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456 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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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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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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408 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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637 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 ...
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Phase change on reflection only 0 and $\pi$ allowed

We know that when a wave on a string is reflected from a hard boundary, the phase change is $\pi$, and from a soft boundary, the change is 0. My question is: this two conditions (hard and soft ...
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Pressure wave in a cup of tea casued by a bubble burst

Assume there is a cup of tea with bubbles formed on its surface by the inner wall of the cup. If one of the bubbles bursts, it causes a wavefront travelling on the surface of the tea. Is this wave ...