What is Amplitude: Definition and 866 Discussions

The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). There are various definitions of amplitude (see below), which are all functions of the magnitude of the differences between the variable's extreme values. In older texts, the phase of a period function is sometimes called the amplitude.

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  1. J

    A Amplitude of a stationary wave

    Does each point in a stationary wave change its displacement and hence it's amplitude? If yes, why is this so? However, why does the amplitude at the node and antinode remains zero and maximum respectively? Does the above have to do with the fact that all the formation of a stationary wave is...
  2. weningth

    A Why does this amplitude not vanish by the Ward identity?

    Consider the process e^-\rightarrow e^-\gamma depicted in the following Feynman diagram. The spin-averaged amplitude with linearly polarised photons is \overline{|M|^2}=8\pi\alpha\left(-g^{\mu\nu}+\epsilon^\mu_+\epsilon^\nu_-+\epsilon^\mu_-\epsilon^\nu_+\right)\left(p_\mu p^\prime_\nu+p_\nu...
  3. R

    Question about finding the amplitude of this circular wavefront

    I'm stumped. How do you get this without knowing the wavelength? Can someone explain how to get the answer?
  4. A

    Help with waveform control: frequency, phase and amplitude

    Hello, I am looking for a controller whether programmable or otherwise that could function as a drive and control circuit which would monitor a transformer output connected to a load and then drive an amplifier with a signal that is proportional to the needed one in order to control the output...
  5. ngrunenberg

    B How do quantum computers find a solution?

    Apologies in advance if this is a stupid question, I'm not the brightest. I recently listened to Scott Aaronson's conversation with Lex Fridman, and an interview he did for Scientific American, regarding quantum computing (QC from now on) and have a question regarding how a QC finds a solution...
  6. E

    Minimum frequency for a point to have maximum amplitude in standing wave

    When I tried using the equations the only thing I could see is that it is impossible for such point to be an anti-node. In this case, how do I find the frequency? The answer is not even with the form of v*n/2L which is very confusing to me, I thought that the frequency of a standing wave must...
  7. J

    MHB Amplitude, Period, frequency and phase angle

    HELP! totally lost and confused with this question: A machine is subject to two vibrations at the same time. one vibration has the form: 2cosωt and the other vibration has the form: 3 cos(ωt+0.785). (0.785 is actually expressed as pi/4) determine the resulting vibration and express it in the...
  8. G

    To find the amplitude of a mass on an elastic string

    Could I please ask for help with the following: It's the final part I am having problems with. So at this point we know we have SHM of amplitude (5/4)L Now, using x = a cos(nt) ----- where we now know that n = sqrt(4g/L) we can find the time at which x has any value. So for exmaple, when...
  9. N

    A Calculation of amplitude with n=5, k=3 using the book by Arkani-Hamed et al

    This is a pretty technical question so before I post all the details, let me first ask if someone might be able to help. I am going over the book Grassmannian Geometry of Scattering Amplitudes and I am trying to calculate the anti MHV amplitude with five particles, at tree level (or...
  10. T

    Simple Harmonic Motion Amplitude

    Using A = x0, B = v0/ω I get ω = 4π, A = 1, B = 1/4π then converting to phase/magnitude form \sqrt{A^{2} + B^{^{2}}} = \alpha \sqrt{1^{2} + \left ( \frac{1}{4\pi }\right )^{^{2}}} = \alpha = \frac{1}{4\pi }\sqrt{16\pi^{2} +1} However the answer in the back of the book has α = 1 Is...
  11. Ammar2211

    A harmonic wave with a frequency and an amplitude

    For part (a), which generic function would be used? either y = f(x) = ASin(2πft + ϕ) or y(x,t)−y0=Asin(2πft±2πx/λ+ϕ) ?? Furthermore how to find out max. speed & max. acceleration of a point on the string?? Any directions please
  12. Saptarshi Sarkar

    Amplitude of oscillation for SHM

    From the first part of the question, I was able to get the value of ω which will be the same for the next SHM. But, I am having difficulties solving for the amplitude as I can't find the boundary conditions required to get the amplitude.
  13. J

    B Photon Energy & Wave Amplitude

    A photon's energy is E=hv where v, the frequency, is a wave property. Particles don't have frequencies. But a wave's energy also depends on its amplitude. Where does this come into the energy relation?
  14. J

    Scattering amplitude in scattering from a delta function

    I tried to calculate the Fourier transform to get the amplitude, but I got lost
  15. R

    Understanding Radio Bands: Amplitude & Frequency

    Just wondering if I understand "radio bands" correctly I am not sure I do. Lets say you have a radio band of 10 GHZ to 30 GHZ and another from 10 HERTZ to 30 HERTZ, the information or a song transmitted will sound the same in those two ranges, the only thing that matters is the amplitude or the...
  16. M

    Exploring the Relationship Between String Tension & Audio Output Amplitude

    I am working on a guitar/piano synthesizer for my own interest. When a string is plucked or struck, tension increases causing a slight pitch bend and change in the inharmonicity. This change then settles as the note quiets down. Thus it is important to model how the tension rises above baseline...
  17. R

    I Calculating a particular amplitude with Feynman diagrams

    So I’m trying to compute the probability amplitude of an electron with momentum p1 and a positron with momentum p2 annihilating into a photons with momenta q1 and q2. My question is how do you use Feynman diagrams to calculate the first and second order expansions (seen in the third image)? I...
  18. Haynes Kwon

    I Why does the square of the amplitude of a wave function represent P?

    Born's postulate suggests if a particle is described a wave function ψ(r,t) the probability of finding the particle at a certain point is ψ*ψ. How does this work and why?
  19. D

    Calculating Divergent Amplitude in Phi-4 Theory

    For the diagram In scalar field theory, I have obtained an integral which looks like $$\int_{0}^{\Lambda} \frac{d^4 q}{(2\pi)^4} \frac{i}{q^2 - m^2 + i\varepsilon} \frac{i}{(p - q)^2 - m^2 + i\varepsilon}$$ I am required to calculate this and obtain the divergent amplitude $$i\mathcal{M} =...
  20. D

    Amplitude of an oscillating electric field

    Homework Statement: The amplitude of the oscillating electric field at your cell phone is 4.0 μV/m when you are 10 km east of the broadcast antenna. What is the electric field amplitude when you are 20 km east of the antenna Homework Equations: electric field i've done E=##\frac A...
  21. PGaccount

    A Vacuum persistence amplitude

    In the functional integral approach to quantum field theory, we have W[J] = ⟨0+|0-⟩J = ∫ D[Φ] eiS + ∫ JΦ Can someone give me some insight into why this path integral is a vacuum-to-vacuum amplitude. How and also why does this path integral W[J] become a vev?
  22. N

    I What exactly is the amplitude of an interaction?

    I've been reading Griffths' intro to elementary particles and I encountered this symbol that looks similar to "M" called amplitude, which can be calculated by analyzing the Feynman diagram of an interaction. What exactly is it? When I hear amplitude I imagine waves, but not sure what this one's...
  23. D

    Finding the amplitude of a vertical spring

    The question asks for a bunch of stuff, but I have everything except part d down. a) Setting the mass of lemons as m1, I used m1*gh = 1/2mv^2, solving for v of the lemons as v = √2gh, where h is the height at which it is dropped. Then, I used COM and had this equation (not 100% sure if right)...
  24. mishima

    Sn(u), Jacobi elliptic function, for simple pendulum of any amplitude

    I understand how to reach $$\int_0^\phi \frac{d\theta}{\sqrt{1-k^{2}sin^{2}\theta}}=\sqrt \frac g l t$$ from physics but from there I don't get how to turn that into this new (for me) sn(u) form.
  25. A

    Amplitude with Feynman diagrams and gluon propagators

    The term which is relevant for the calculus is: $$ \bar u(p) \gamma^\alpha \frac{1}{\displaystyle{\not}p+\not k} \gamma^\nu \frac{1}{\displaystyle{\not}p'-\not k} \gamma^\beta v(p') \frac{k_\alpha k_\beta}{k^2} $$ $$ \bar u(p) \displaystyle{\not}k \frac{1}{\displaystyle{\not}p+\not k}...
  26. VicomteDeLaFere

    I Oscillation with constrained amplitude

    Hello, Suppose we have a simple oscillating spring mass system. The natural frequency will excite the system to have infinite amplitude. Suppose then, that we have that system on a table so that amplitude is limited. I'm imagining the high school experiment with the spring mass system on the...
  27. paulmdrdo

    Maximum Amplitude of a Function

    I was able to find the maximum value for this function by differentiating and equating it to zero and find the time t and substitute it back to the original expression to get the max amplitude. tm = -0.001012 s v(tm) = 56.6 Another method that was presented in my book was can you explain how...
  28. C

    I Relation between tensor decomposition and helicity amplitude

    It is common to write e.g photon two point function in terms of manifest transverse and longitudinal form factors with lorentz structure factored out, e.g $$\Pi^{\mu \nu} = (g^{\mu \nu} - q^{\mu} q^{\nu}/q^2)T_T + q^{\mu} q^{\nu}T_L,$$ where mu and nu are polarisation indices. How do I relate...
  29. Shivang kohlii

    Shm , calculation of amplitude of spring mass system

    Homework Statement In A spring mass system , the spring stretches 2 cm from its 's frelength when a force of 10 N is applied . This spring is stretched 10 cm from it's free length , when a body of mass m = 2 kg is attached to it and released from rest at time t = 0 . Find the A) force constant...
  30. L

    A Quantum amplitude for a particle falling into a black hole

    Here we consider a black hole formed by gravitational collapse classically. We also consider a scalar massless Klein-Gordon field propagating on this background. To quantize the field we expand it in appropriate modes. The three sets of modes required are: The incoming modes, appropriate for...
  31. S

    Amplitude relation with periodic time

    Homework Statement Ql: Which sound wave will have its crests farther apart from each other - a wave with frequency 100 Hz or a wave with frequency 500 Hz? Homework Equations Frequency= 1/ periodic time The Attempt at a Solution I did it like that: I just found the periodic time for each...
  32. F

    Standing waves on a string experiment -- Relative amplitude of harmonics

    Hello forum, I am wondering why the higher order (higher harmonics) standing waves developed on a string under tension generated by an oscillating mechanical vibrator (set at the same amplitude but with variable frequency) have lower amplitude when compared to the lower harmonics (the...
  33. OnlinePhysicsTutor

    Resultant amplitude of 6 phasors

    Homework Statement This is a problem from one of my students, he is taking an undergrad module in optics. Most of the question is fine but I cannot see a neat solution to part ii Homework Equations These are the equations for the topic, but I am not sure if we are missing the relevant...
  34. M

    Does amplitude depend on mass in SHM?

    Homework Statement Does amplitude of an oscillating spring with an attached block depend on the block's mass? Assuming the spring has spring constant 'k' and obeys Hooke's law. How would the amplitude of the oscillating spring system be affected if the mass of the block were...
  35. F

    Vibration testing on shaker - High amplitude observed

    Hello everyone, I wanted to gather opinion from anyone experienced in vibration regarding one of test fixtures I have created for small satellites. The image below shows the Test-POD that I am testing on a single axis shaker. In one of the tests, I had troubles that the amplitude got higher than...
  36. B

    I Amplitude and Multiplication

    When we multiply psi sub x, psi sub y, psi sub z and psi sub t together to get a function of all four variables, does each separate wavefunction have a radius of one such that the radius is unchanged after the multiplication or is their radius far smaller than one? Secondarily, can this...
  37. Shivang kohlii

    Amplitude of a mass joined to a spring in the presence of an E-field

    Homework Statement A block of mass m having charge q placed on smooth horizontal table and is connected to a wall thorough an unstretched spring of constant k . A horizontal electric field E parallel to spring is switched on. Find the ampliture of the shm by the block. Homework Equations kx=...
  38. Izzy Levine

    Help please -- Amplitude of a spring - does it change with mass?

    Hello! In some of my college Physics practice problems, amplitude of a spring in Simple Harmonic Motion does not change with mass (for example, when the mass splits in 2 at equilibrium in a horizontal oscillator - see picture). But, in other problems, the Vmax of the oscillator remains constant...
  39. Cc518

    Calculating τ by knowing I is proportional to A^2

    Homework Statement A vibrating standing wave on a string radiates a sound wave with intensity proportional to the square of the standing-wave amplitude. When a piano key is struck and held down, so that the string continues to vibrate, the sound level decreases by 8.0 dB in 1.0 s. What is the...
  40. Raymont

    Divergence of the amplitude for a Feynman diagram

    1. The problem statement In calculating the amplitude for the diagram[1], view 1.jpg. [1] Voja Radovanovic, Problem Book Quantum Field Theory 2. Homework Equations View 2.jpg. The Attempt at a Solution View 3.jpg.[/B] Why the integrals is divergent? Why the other terms are finite?
  41. ParticleMan

    Amplitude vs Magnitude: Explaining the Probability Density

    While trying to get a better understanding of amplitude vs magnitude, something I should frankly already know, the following video popped up near the top of my google search. Hmm...anything to point out? How many things? But seriously, how would YOU explain amplitude vs magnitude? Would...
  42. J

    Quarter amplitude response method: PID settings

    Homework Statement see attached, question 8a and b are what I'm attempting. I've also attached the VERY brief course notes that I'm required to work with. I know Tc= 8 seconds from the graph (0.13minutes) Gain set to 4. is PB therefore 100/4=25%? I'm struggling to calculate the ratio of...
  43. D

    Standing wave transverse motion and amplitude

    Homework Statement A guitar string is vibrating in its fundamental mode, with nodes at each end. The length of the segment of the string that is free to vibrate is 0.381m. The maximum transverse acceleration of a point at the middle of the segment is 8600 m/s and the max. transverse velocity is...
  44. G

    Weak Damping - how to relate the amplitude and phase difference

    Homework Statement Derive the relationship bewteen x_{max}, A_{+}, A_{-} and \phi Homework Equations x(t) = e^{\gamma t}(A_{+}e^{i \omega_d t} + A_{-}e^{-i \omega_d t}) x(t) = x_{max} e^{\gamma t} cos(\omega_d t + \phi) The Attempt at a Solution I know the e^{\gamma t} cancels and for the...
  45. C

    Change in the amplitude of a damped spring block oscillator

    Homework Statement A block is acted on by a spring with spring constant k and a weak friction force of constant magnitude f . The block is pulled distance x0 from equilibrium and released. It oscillates many times and eventually comes to rest. Show that the decrease of amplitude is the same...
  46. Cathr

    Electromagnetic wave equation - phase and amplitude

    There are some things that confuse me about electromagnetic waves, and I haven't found good answers anywhere. Consider the following equation: E=E0 e i(wt-kx) (here E and E0 are vectors, I couldn't find the right symbols). The things that confuse me are the following: 1° We say that the power...
  47. Ramtin123

    A Computing amplitude for divergent loop diagrams?

    I am trying to compute the cross-section for the diagram below with a divergent triangle loop: where ##X^0## and ##X^-## are some fermions with zero and negative charge respectively. I am interested in low energy limits, so you can consider W-propagator as ##\frac {i\eta_{\mu\nu}} {M_w^2}##...
  48. nomadreid

    I Arc length constant, despite varying the period via varying amplitude

    This is not a school problem, just my own mucking about, but since it has the form of a problem, I am willing to shift it to the "homework problems" rubric. If there is a theoretical string (no thickness, etc.) that is non-stretchable tied to two endpoints and is long enough to be able to form a...
  49. P

    A Why does sd replace sγ5d ee in the amplitude of meson decay?

    is the amplitude of pure leptonic decay of pseudo scalar meson(say K→ee), while is the amplitude of the semileptonic decay of K→π ee. Kindly explain why does sd replace sγ5d ee in the amplitude?
  50. R

    Amplitude problem — Car shock absorbers going over a bump

    Homework Statement -(View image attached)[/B] A driver drives a car.The road has periodic small bump of 5 cm height and a distance of 5 cm. Car's shock observer works fine,damping the deflection to half each oscillation.Their length is 20cm increased if car weight(1500kg) does not...
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