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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Why is a subwoofer bigger than a tweeter? [duplicate]

I came across this video - The Fundamentals of Sounds - where it says in 14:00: Subwoofer is larger because it needs to be bigger for those larger low frequency waves to propagate through and the ...
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Relation between the electric and magnetic fields for an arbitrary electromagnetic wave

When solving the wave equation for electromagnetic waves, $$ \nabla^{2} \mathbf{E}=\mu_{0} \varepsilon_{0} \frac{\partial^{2} \mathbf{E}}{\partial t^{2}}, \quad \nabla^{2} \mathbf{B}=\mu_{0} \...
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Propagation of electromagnetic waves

When EM waves propagate, they produce oscillating electric and magnetic fields. How did we know this? Is there any experimenting concluding this or it this just a theory?
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How can I visualise waves?

A wave is a sustained disturbance produced at a point in a medium(or field) and is transmitted to other parts of the medium(or field) without the actual translatory motion of the particles. This ...
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Wave equation and skin-depth

I initially posted this question to the math stack overflow, but realized that it is really a physics question This is a follow-up question to one of my unanswered questions https://math....
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What determines the frequency of the wave at the coffee/milk boundary of my iced coffee?

As I set down my iced coffee, which I made by first pouring a bit of milk over ice, then adding hot coffee over ice without stirring, I noticed that the jolt of setting down the glass had set up a ...
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Electrostatic ion cyclotron waves

On page 102 of the 3rd edition of F.Chen's introduction to plasma physics and controlled fusion, he discusses the phenomenon of an ion acoustic wave propagating at right angles to a magnetic field $\...
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Can a wave be modulated in such a way such that it can calculate the time the wave existed from the transmitter to the receiver

Can a wave be modulated in such a way or by any other techniques or program it? I know it sounds impossible but can there be a way to do the above task?
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Direction of propagation of electromagnetic waves

I have a differential equation for an electromagentic wave propogating in the z-direction and oriented alone the x-axis: $$\frac{d^2 E_x}{d z^2}+\omega^2 \mu \epsilon E_x=0$$ and if I say $k^2= \omega^...
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Alternate forms for the wave equation?

Are there alternate ways to write the usual wave equation?: $$ \frac{\partial^2u}{\partial t^2}=c^2\nabla^2u. $$ I've come across this equation in a paper (Yoshimura 1975): $$\frac{\partial^2\Psi}{\...
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A question regarding waves and photoelectric effect

I was reading my physics textbook and there was an example in it in which an electromagnetic wave whose electric component varied with time as $$E=a(1+\cos\omega t)\cos\omega_0t$$ was incident on a ...
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Why speed of sound in gas depends on density but not pressure?

The book tells that with decrease in density there is an increase in speed of sound in gas but with increase in pressure there is no change in the speed of sound in gas. Why? If pressure increases ...
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About Oscillation in Gravitational wave [duplicate]

I am a high school student studying about gravitational waves. I hope they are similar to other waves like sound waves, etc. So I what to know exactly what oscillates in a gravitational wave. Like in ...
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What are waves? [duplicate]

I am layman when it comes to physics, but I cannot understand what is often meant when waves are discussed. I understand physical waves, e.g. water, as a type of behaviour of some fluid or medium. So ...
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Cause of 180 degree phase shift of reflected light [duplicate]

When light originating from a medium of lower refractive index reflects off a surface of higher refractive index, why does the phase shift by 180 degrees? Stokes relations show that the reflection ...
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What is the optimal shape for a satellite dish?

How do I find the equation of that shape if all I know is that it focuses reflected waves into one point? I guess I'm supposed to get a parabola.
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Potential and Kinetic Energy of a Travelling Wave

In a book(that I was going through), it is given that the kinetic and potential energy of a travelling wave is always the same but the proof for this statement is not given. Kindly express your ...
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A problem related to Doppler Effect

Will Doppler Effect of sound waves be observed if the waves are observed from a frame that is moving with a constant velocity with respect to the frame in which the waves are being produced ( where ...
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Calculate the absorption of light using time averaged pointing vector (from RCWA simulation)

GOAL: I would like to compute the local absorption of light in material from an RCWA simulation. The RCWA tool can output the time-averaged (and input-normalized) Poynting vector. The time-averaged ...
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Deriving speed of waves equation [duplicate]

I am trying to derive the speed of a wave equation $$v = \sqrt{F/\mu}$$ starting from a segment of string under tension with a force of $F$ in which a pulse moves with a speed of $v$. Can someone show ...
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Can we maintain a standing wave in a slowly growing box?

I believed that the answer to that simple question was 'yes', until I was thinking more about it recently, and now I have a doubt. Consider a simple standing wave in a 1D "box" of length $...
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How sensitive is double-slit result to a fixed wavelength?

I was watching a video on the double-slit experiment, and the lecturer (*) mentioned, in passing, that the frequency of the waves must be kept the same. (Still in the context of water waves at this ...
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Dispersion relation for electron plasma waves at large and small wavelengths

I am currently reading F.Chen's Introduction to Plasma Physics and Controlled Fusion On page 83, he derives the dispersion relation for the electron plasma wave: $$ \omega^2 = \omega^2_p + \frac{3}{2}...
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How to find the longitudinal waves in an elastic bar hanging from the ceiling?

The vertical displacements $w(y)$ in a bar hanging from a fixed point, due to its own weight, compared with the unstressed configuration follow a quadratic equation, that solves: $$E\frac{\partial^2 w}...
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EM wave power dependency on frequency

Does a (classical) radio wave with a given amplitude carry more power if that wave is at a higher frequency than at a lower frequency?
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Fraunhofer diffraction and lens

[This image is collected from the Fraunhofer diffraction article of wikipedia] Fraunhofer diffraction and lenses In Fraunhofer diffraction the source is infinitely away from the lens and screen which ...
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Interference and superposition of waves

In the picture above, black and blue lines are representing waves(mechanical) emerging from the slits(after diffraction). Let us consider that at point A, centre of a bright fringe is located. That ...
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How to know direction of propagation of wave? [closed]

I thought a way but don't know whether it is correct or not. Like equation of wave is $$y=A\sin(±wt±kx±\phi)$$ one way is keeping input of sine constant which visually means that we are indicating a ...
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The role of the separation constant when solving the wave equation for electromagnetic waves & Cut off wave number

I have the following wave equation that I need help to solve via separation of variables: $$\nabla^2 \mathbf{E} + k^2 \mathbf{E} = 0$$ Where E is the electric field and k is the wave number Using ...
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Show that the segmentation of the Amplitude is consistend with the conservation of energy (Reflexion)

So. For a P-Wave perpendicular to the layer boundary: Z: Impedance A: Amplitude E: Energy $P_R=$reflected Wave, $P_T=$transmitted wave, $P_I=$incoming wave I got the reflexion coefficient $$R=\frac{...
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Making equal arguments of sine or cosine function

I have trouble understanding one common type of inference about waves. In physics textbooks, frequently when text is about waves I see inference where arguments of trigonometric functions made equal ...
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What is the difference between $v=fλ$ and maximum velocity in the formula $v=ωY_{\max}$? [closed]

I was wondering what the difference is between speed in the formula $v=fλ$ and maximum velocity in the formula $v=ωY_{\max}$ as applied to a wave.
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Superposition of waves

Let two waves moving in the direction from $D$ to $B$ and $C$ to $A$. These waves are out of phase at $O$. Then will the particles along $OA$ and $OB$ oscillate? If they do oscillate,then can you ...
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Can the electric field of an EM wave have a component in the direction of the wave?

I am currently taking a course in electromagnetics and i've stumbled into a problem. On the Engineering electromagnetics book by sadiku there is a question with the electric field of plane wave as ...
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Do incoherent sources of waves mean that the frequency of the sources are different?

I studied that coherent sources of waves are those sources that maintain a constant phase difference between the two waves as time passed and incoherent sources are ones that don't. Does this imply ...
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Calculating $\Delta V_{sound}$ when $\Delta T = 1 K$ when $v_{sound}$ at 273 K = 332 m/s

Here is my solution We know that $v_{\text{sound wave}} = \sqrt{\frac{\gamma RT}{\rho}}$ which means that $v_{\text{sound wave}}\propto T(\text{in Kelvin})$ $\implies \frac{v_1}{v_2} =\sqrt\frac{T_1}{...
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Doubt on the predictions on the photoelectric effect according to the wave theory of classical physics

I read in some texts that classical physics predicted the following in the photoelectric effect, KE of electrons ejected is directly proportional to intensity of light Increasing the frequency would ...
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Do any other waves work like light waves in that one "thing" gives rise to another thing?

My understanding of light is that there are two types of fields involved, electro and magnetic fields and one causes the next which then causes the other type and so on. Is light the only thing that ...
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How is it that Increase in amplitude of electromagnetic radiation results in increase in number of photons

I cannot comprehend how the increasing of amplitude of an electromagnetic wave increases the number of photons. How does this even happen. I am also not able able to make sense of that fact that, when ...
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Right-hand rule of EM waves (electric, magnetic field and direction of propagation)

According to my physics book, the electric field, the magnetic field and the direction of propagation obey to right-hand rule. Anyway I am not sure why in the pictures below the book states that $B = \...
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How do Standing Waves satisfy the criteria in order to be considered as Waves?

Why are standing waves even categorised as waves if they don't transfer energy from one point to another? Waves are generally defined as disturbances that transfer energy but standing waves don't ...
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Can we use the equations $-AωSin(ωt+φ)$ and $AωSin(ωt+φ)$ interchangably?

My book says that, For a simple harmonic motion, velocity of the particle = -AωSin(ωt+φ) Now, assuming φ to be π/2, in the next sentence, they say that, maximum velocity = Aω. Why have they simply ...
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Is it also the case that $\langle f(t)\rangle = 0$ for $f(t) = A \cos(\omega t)$? And how does one get that $\langle f(t)\rangle = 0$?

This page discusses time averaging. It says that time averages are often important when considering oscillating waves of the form $f(t) = A \sin(\omega t)$, where $\omega$ is the angular frequency and ...
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Why light shows its wave-like properties only when it interacts with objects with dimensions close to the wavelength of light?

In Young's Double Slit Experiment, we were taught that light behaves as a wave here because the width of the slits are very close to the wavelength of light itself. But why does light behave like a ...
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The resonance frequency of a steel ball

I wanted to find the resonance frequency of a steel ball. I assume that gradient disappears on the surface of a ball. I knew that I can find it solving 3D wave equation in spherical coordinates. Due ...
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Speed $v$ of a wave on a tightrope

Starting from D'Alembert's general wave equation we can find the propagation speed of an impulse along a tightrope as a function of linear mass density, $$\boxed{v= \sqrt{\frac \tau \mu}} \tag 1$$ ...
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Do acoustic waves in liquid crystals have transverse modes?

According to a previous question: Modes of propagation in media acoustic waves in media can be decomposed in two kinds of modes: longitudinal and transverse; solids being the only one where they are ...
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Wave packet in quantum mechanics?

When we talk about light waves or EM waves, we simply say that the wave packet is the superposition of other waves of different wavelengths. In quantum mechanics, we say the same thing; the ...
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The lowest possible frequency of sound wave

What is the lowest possible frequency of sound waves. I imagine that if a plate vibrates slower and slower it stops producing sound and starts to just 'move' the air around. What is this minimum ...
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What is the difference between beats and wave packets?

What is the specific difference between beats and wave packets. According to my book both are the formed by superposition of two waves having slightly different frequencies

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