# Questions tagged [waves]

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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### Calculation of the reflected wave amplitude in a string [closed]

I have a problem to calculate the reflection amplitude of the wave when a wave passed to another medium with different density. To obtain the amplitude of the reflected and transmitted wave, I ...
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### Why the Electrical field is that way? [duplicate]

So, I asked my teacher to draw the incident and reflected wave in the case of the incidence onto a perfect electric conductor. The thing I Don’t undersand is why the reflected field is that way. The ...
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### How can we derive the polarization of reflected electric field? [closed]

Simply out: How can we derive the polarization of a reflected electric fields in the case of parallel polarization, where the electrical field lays on the incidence plane
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### Why do airplanes sound louder when its cloudier?

I am from India, and now its monsoon season. Typically, during this time, the sky is filled with dark rain clouds. Me, along with several of my friends, have observed from childhood that the planes ...
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### Formal description of an electron absorbing a photon

This question is about how the electromagnetic field interacts with matter. Suppose we have an electromagnetic wave, let us say it is planar but not monochromatic. So the wave is described by an $L^1$ ...
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### Can taut membranes and strings that are clamped at both ends propagate non-standing waves?

I'm going through an introductory course in acoustics and I'm struggling with the intuition behind standing waves. When deriving solutions to the various wave equations we usually impose a boundary ...
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I know that for the heat equation $u_t=\nabla^2u$, the steady-state condition $u_t=0$ suggests we need to solve $\nabla^2u=0$ (i.e. Laplace's equation), which yields the equilibrium temperature ...
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### How to "rectify" this wave-equation derivation for Longitudinal waves?

To derive the differential equation for longitudinal waves, my professor proceeded like this: We are using the concept of $N$-coupled oscillators. Consider a slab of length $l$ and cross sectional ...
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### How to show the ratio (spin angular momentum density)/(energy density) for circularly-polarized gravitational plane wave = $\pm 2/\omega$?

It is well understood that an infinite monochromatic, circularly-polarized electromagnetic plane wave has no angular momentum density. However, a finite monochromatic, circularly-polarized ...
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### When a taut string is plucked, what will be the direction of the transverse wave's propagation?

Intuitively, I'd guess that the direction of propagation depends on where you pluck the string, namely which half of the string. In the case of a stringed instrument, this guess of mine would ...
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### How was the speed of colored light measured in a vacuum? [closed]

Light is affected by the change in the speed of the source as the frequency of light changes. This is called the Doppler effect, where the red shift can be observed in galaxies moving away from us. ...
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### Lamb wave derivation: Elastic wave propagation in a thin sheet

I am trying to follow the derivation for the phase velocity for elastic waves with large wavelengths compared to sheet thickness, propagating in a floating ice sheet, as described in Propagation of ...
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### Is the Doppler Effect for sound waves with a moving source due to the fact that the wave speed is independent of the source?

The Doppler Effect is typically formulated as follows: $$f' = \dfrac{v \pm v_o}{v \mp v_s} \cdot f$$ The reason for the frequency increasing for observer moving towards source seems clear enough. It ...
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### An echo that sounds for years?

How exactly should I understand United Airlines Flight 2860's description and English Wikipedia? Namely, last sentence of the fourth chapter of the summary: The "echo" of the crash could be ...
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### Physical basis of "forced harmonics" on a violin

I have recently learnt of a somewhat novel violin technique, sometimes known as "forced harmonics", where, in a physicist's terms, instead of the normal N=1 stationary wave (fundamental mode)...
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### Diffraction when the wavefront is not parallel to the plane

I am studying Feynman's chapter on the origin of the index of the refractive index (see this link). If I am not mistaken, what he does is to prove that when a wave enters a medium (modelled as a ...
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### The "small amplitude" assumption in the derivation of the wave equation for the string

I am reading about the wave equation for transverse waves in a string from the book Mathematics of wave propagation (2000) by J. Davis. On page 10, just before the derivation of the (one-dimensional) ...
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### Directionality of EM Waves in Double Slit Experiment

In the experiment of any wave through the double slit we see and model the interference pattern as shown. In this depiction that means the wave propagates in/out of the page. ie we are seeing a sin ...
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### Phase Slope Distance Calcuation

After trying to implement IFFT algorithms for phase-based ranging, as outlined in this very interesting and descriptive blog post; I've been getting horrendous results (orders of magnitude inaccurate),...
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