What is Amplitudes: Definition and 108 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. H

    Constructive and destructive waves with equal amplitudes?

    1. If two wave lengths have the same amplitude and have the exact same phase(360 degrees, 0 degrees, or 2pi) and is constructive, will the amplitude double? 2. If two wave lengths have the same amplitude and are exactly out of phase(180 degrees, pi) will the resultant wave have a straight line?
  2. A

    What is the ratio of wave amplitudes at two sites with 5dB attenuation?

    Homework Statement Doing my own independent study, and I've come across a textbook question I'm rather lost on. Problem: Over the distance between two seismic recording sites at different ranges from a seismic source, seismic waves have been attenuated by 5dB. What is the ratio of the wave...
  3. D

    Amplitudes of Electromagnetic Waves Question

    So I can't find this anywhere, but I would really like an answer as it's driving me up a wall; Are the amplitudes of all electromagnetic waves the same, and if so how are the speeds of the particles that move along the wave not > c? Thanks in advance.
  4. V

    When getting phase angle difference, do amplitudes have to be positive

    $$f(x)=32sin(x+60°)\quad and\quad g(x)=-1.5sin(x+45°)$$ Would the phase angle difference here be 15° or is that incorrect? I think the amplitudes don't have to be the same but I'm not sure if they at least have to be both positive.
  5. C

    Graph Amplitude and Phase of x(n) and x(t)

    Say x(n) = n for 0 <= n < 4 and 0 o.w. So X(W) = Sum n=-∞ to ∞ x(n) exp(-inw) = sum from n=0 to 3 nexp(-inw) = 0 + exp(-iw) + 2exp(-j2w) + 3 exp(-j3w) get do I get the amplitude and phase? Also if the signal was continuous x(t) = t for the same interval X(W)= integral 0 to 4 texp(-iwt)...
  6. R

    Determining the damping constant from the ratio of amplitudes

    Homework Statement I have measured the amplitude between the first and tenth oscillations for a damped harmonic oscillator (spring with a mass attached). I also have measured the period. First question. Is an (underdamped) harmonic oscillator periodic? Like I know that the solution to the...
  7. B

    Elektromagnetic field ~ probability amplitudes

    Given an electromagnetic field by its components E and B. How is this related to probability amplitudes of a Schrödinger wave function for the same field. Trying the same or at least a similar question from a different angle: given the E and B field, can we derive from it, in principle, not...
  8. D

    Can Amplitudes Be Assigned Between Subspaces in Quantum Mechanics?

    The amplitude for a state |\psi\rangle to be in the state |\chi\rangle, with both states represented as vectors in a complex Hilbert space, is a complex number whose modulus squared gives the probability that a system in the state |\psi\rangle is found to be in the state |\chi\rangle after...
  9. S

    QFT: Scattering Amplitudes in Yukawa Theory

    Homework Statement I'm working with the Yukawa theory, where the interaction term in the Lagrangian density is g\varphi\overline{\psi}\psi. As an exercise for getting used to using the Feynman rules for the theory, I'm asked to show explicitly (i.e. I'm not allowed to invoke charge...
  10. S

    What properties determine whether a set of amplitudes forms a vector space?

    Homework Statement What properties cause complete sets of amplitudes to constitute the elements of a vector space? Homework Equations The Attempt at a Solution Does the question mean 'a vector space' or 'a linear vector space'?
  11. S

    Quantum amplitudes versus probability

    Lately, I've been wondering that the sum rule from probability theory applies in all fields of study, expect for in quantum mechanics, where we need to apply the sum rule to probability amplitudes instead of to probabilities. Is there any physical phenomenon that can explain this principle...
  12. A

    Scattering Amplitudes BCFW relation (A question)

    I have a very trivial question to ask and it would be great if someone could help me in this. The statement that '3-point amplitudes' and the location of poles are sufficient to determine any n-point amplitude at tree level is confusing to me. Don't I also need to know 4-point amlitudes, for...
  13. F

    Sound waves question - vibrations and amplitudes

    A tuning fork vibrates 235 times in 3.1 seconds with an amplitude of 0.59mm. Determine.. i) its frequency ii) its period iii) the distance the end of one of the fork tines travels in one second for i) The answer I got is f=75.81Hz ii) The answer I got is 0.13s iii) ?
  14. B

    Ratio of Damped to Initial Oscillation Amplitudes - 20 Cycles

    In the figure below, a damped simple harmonic oscillator has mass m = 300 g, k = 95 N/m, and b = 70 g/s. Assume all other components have negligible mass. What is the ratio of the amplitude of the damped oscillations to the initial amplitude at the end of 20 cycles (Adamped / Ainitial)? I...
  15. L

    Calculating RMS Value for Unequal Peak Amplitudes

    If I have a wave that looks pretty much sinusoidal but the peak positive amplitide is greater than the peak negative applitude how do I calcualte the rms vlaue - is it still the peak positive amplitude divided by root 2? Thanks :)
  16. C

    Why Does Quantum Mechanics Use Complex Probability Amplitudes?

    Im new to quantum mechanics and prof. James Binney writes the probability amplitude of going through two paths s and t, is the mod square of A(s)+A(t). Then he writes this as The mod square of A(s)+ mod square of A(t) + A(s)A(t)* + A(t)A(s). Why is it expanded like this? Could someone please...
  17. E

    Amplitudes in CFT vanish. Why does N=4 have them?

    Hi guys, one question in this growing amplitude business that i don't understand. Usually one says that conformal field theories do not have any non-trivial scattering amplitudes because one cannot define asymptotic states. But say we consider now N=4 Super Yang Mills and moreover treelevel...
  18. G

    Gauge invariance & mass shell amplitudes & pdfs

    What is means that unintegrated parton distributions and matrix elements are supposed to be gauge invariant??
  19. F

    How to find the amplitudes and polarisation of travelling waves

    Homework Statement Plane monochromatic waves are propagating in free space parallel to the x-axis in both positive and negative directions. At the origin the fi eld strengths are given by: Ez = E0 cos wt Ey = 3E0 cos wt cBz = E0 cos wt cBy = E0 cos wt Find the amplitudes and...
  20. M

    Measuring intensity of superposed waves using complex amplitudes

    Hi, Suppose we have the x and y components of the electric field being described as (E_{x}e^{i(kz-\omega t)}, E_{y}e^{i(kz-\omega t +\phi)}), what is the intensity? I think the correct answer is E_{x}^{2} +E_{y}^{2} + 2E_{x}E_{y}\cos\phi. However, I am not sure how to deal with this using the...
  21. nomadreid

    Short question about probability amplitudes

    When one says the probability amplitude for a quantity when it has probability P, which one does one take, the a+bi or the a-bi?
  22. P

    Probability amplitudes and photons

    Suppose a Fock state contains 2 photons, both in the same spacetime mode and having the save (vertical) polarization. So we can write this state as |2>, or, if we want to emphacize its vertical polarization, we may write |2v> or |2v,0h>. Suppose now we want to measure polarization in the...
  23. P

    Conformal invariance of gluon amplitudes

    Hi, I'm very ashamed to not understand how even the simplest gluon amplitudes are conformally invariant. See eg http://arxiv.org/abs/hep-th/0312171 pages 11-12. M(1^-,2^-,3^+)=\delta(\sum_i \lambda_i\tilde{\lambda}_i)\frac{\langle12\rangle^4}{\langle12\rangle \langle...
  24. Y

    Tricky spring problem. Amplitudes and AccelerationMax

    Homework Statement A block with mass m =6.7 kg is hung from a vertical spring. When the mass hangs in equilibrium, the spring stretches x = 0.26 m. While at this equilibrium position, the mass is then given an initial push downward at v = 4.7 m/s. The block oscillates on the spring without...
  25. C

    Find electric and magnetic field amplitudes in an electromagnetic wave

    [Solved] Find electric and magnetic field amplitudes in an electromagnetic wave Homework Statement Find the electric and magnetic field amplitudes in an electromagnetic wave that has an average energy density of 1 J/m^3 Homework Equations u = Energy density u = (1/2)(e0)(E^2) +...
  26. S

    Time independence of probability amplitudes

    What's wrong with the following: \frac {d \left< E_{k} | \Psi \right>}{dt} = \frac{\partial \left< E_{k} \right|}{\partial t} \left| \Psi \right> + \left< E_{k} \right| \frac{\partial \left| \Psi \right>}{\partial t} = \frac{i}{\hbar} \left< E_{k} | H | \Psi \right> - \frac{i}{\hbar} \left<...
  27. O

    Spectrum estimation with noisy data, unbiased estimation of amplitudes needed

    hi everyone, i would be grateful for suggestions for the following problem: i have a set of measurements, discrete samples from a continuous function of time. with each measurement comes a estimate of its uncertainty (standard error). by doing a discrete Fourier transform, i have seen some...
  28. K

    Beam splitter->ONB->transition amplitudes

    Homework Statement a general beam splitter is charcatericed by its transition amplitudes Sxy=<Xin|Yout> where X,Y=L or R. |Lin> represents a photon which leaves the beam splitter to the right. we are only considering photons with the same energy and polarization and neglect all other state...
  29. P

    Voltage amplitudes across inductor and resistor

    Homework Statement A series combination of a 22.0 mH inductor and a 145.0 ohm resistor are connected across the output terminal of an ac generator with peak voltage 1.2 kV. (a) At f= 1250 Hz, what are the voltage amplitudes across the inductor and across the resistor? (b) Do the voltage...
  30. B

    If two wave of different amplitudes superpose at a point, would each

    if two wave of different amplitudes superpose at a point, would each wave leave this point with the same amplitude before superposition, or will they leave the point of superposition with equal amplitudes?
  31. E

    How Do You Calculate Wave Functions Across a Potential Step?

    Homework Statement A beam of particles of energy E and incident upon a potential step of U0=5/4E is described by the wave function; \psi(x)_{inc}=1e^{ikx} Determine completely the reflected wave and the wave inside the step by enforcing the required continuity conditions to obtain...
  32. inflector

    What Does Quantum Gravity Scattering Amplitudes Mean?

    What Does "Quantum Gravity Scattering Amplitudes" Mean? I've seen it referenced in a few papers but I can't seem to find a definition. I know what "scattering amplitudes" means but don't understand the relationship with quantum gravity. What precisely is doing the scattering in quantum gravity?
  33. B

    Unraveling the Mystery of Probability Amplitudes

    Homework Statement What physical phenomenon requires us to work with probability amplitudes rather than just with probabilities, as in other fields of endeavour? Homework Equations The Attempt at a Solution Not sure. The wording of the q throws me... phenomenon i.e...
  34. O

    Analytic properties of amplitudes

    Hey, I have been looking around for a good resource explaining the analytic properties of Feynman diagrams and their resulting amplitudes. I think I understand in general what to expect (branch cuts for multiparticle states, poles for single particle states and bound states), but I'm not...
  35. T

    Modal amplitudes of circular plate

    Hi all, I'm a final year acoustics student in the UK attempting to model the modal response of a circular plate as part of my thesis. Essentially, i have this equation : and I am trying to deal with the left term of the LHS. I'm trying to find out whether the full version of...
  36. M

    Divergent partial wave amplitudes

    I want to calculate the partial wave amplitudes for various processes but get divergent results in certain cases which I assume is related to the propagator going on shell - the forward scattering amplitude is infinite. I guess I have to introduce some sort of cut but don't know how to do this...
  37. M

    Quantum - Projection Probability - Projection amplitudes for SHO states.

    Quantum - Projection Probability - "Projection amplitudes for SHO states." Given the two normalized 2D SHO wave functions <x,y|mx[/SUB ],ny> for the second energy level n = nx + ny = 1 in the m[SUB]x[/SUB ],n[SUB]y representation: <x,y|1,0> = (2/pi)1/2xexp[-(x2+y2)/2] <x,y|0,1> =...
  38. C

    Solving 4-Vectors and Wave Amplitudes in Different Frames

    Homework Statement I am aving a bit of trouble understanding how to show something is a 4 vector. For example K = (v/c, 1/lamdba, 0, 0 ) Show it is a 4-vector. I am not quite sure how to start this. Similarly I have the amplitude of a wave in frame S described as A=cos[2PI(vt-x/lambda)] and...
  39. E

    Deduce Kinematic Factors Easily: No Tedious Work

    I want know if have a procedure aesy of deduced the kinematic factor. I know the procedure of M.B. Green pp 420, but is tedious.
  40. H

    Sketching EM Waves with imaginary amplitudes

    Homework Statement Sketch in 3D, the following waves. (both E fields are in x direction E_1 = 3*exp(-j*8*Pi*z) E_2 = 4j*exp(-j*8*Pi*z) (where j=sqrt(-1)The Attempt at a Solution I know how to sketch E_1, but my question is how to treat the imaginary amplitude, 4j in E_2. here is my stab at...
  41. redtree

    Probability amplitudes, de Broglie and Schrödinger

    What is the relationship between the "matter waves" described by de Broglie, the probability amplitude function and Schrödinger's wave equation? I've read the following: "The wavelengths postulated by de Broglie to be associated with the motions of particles are in reality the wavelengths...
  42. F

    What are the amplitudes called for blue visible light, and microwaves?

    The amplitude of sound waves is commonly referred to as volume. What about for blue visible light, and microwaves? I'm guessing for the first one it's brightness. Btw I'm looking for a word answer, not the magnitude of the amplitude (not a numerical amplitude) Thanks for reading.
  43. B

    Wave Composition - Different Amplitudes

    Homework Statement The superposition of two waves, [see attachment - it doesn't let me link the attachment because I'm new ;P] at the location x = 0 in space results in what kind of wave behavior? [As in, how often does it beat and what frequency is the sound?] Homework Equations Wave...
  44. I

    Superposition, amplitudes and superposed waves.

    First off: Sorry. I'm a Norwegian girl, so my English may not be of very good quality. Now that's said... I have this problem to solve. Only thing is - I don't have a clue how! I'm no good at physics, but unfortunately I have to have this class. Anyway. My problem is this: Task...
  45. M

    What is the ratio of the amplitudes of the two waves?

    Homework Statement Two earthquake waves of the same frequency travel through the same portion of the Earth, but one is carrying ten times the energy. What is the ratio of the amplitudes of the two waves? Homework Equations I=Intensity A=Amplitude P=Power I=A^2 The Attempt at...
  46. H

    Pendulum with larger amplitudes

    Homework Statement I really would like some help. Next month I am starting a project with the title "pendulum with larger amplitudes", where I have to come up with a solution on how to solve the equation for the pendulum with large amplitude. Homework Equations This is the equation I...
  47. F

    Amplitudes, metrics, and measures

    This is a question about how the amplitudes of QM might be generalized. I'm not sure this post belongs here or perhaps some other forum. But I believe I am talking about extending QM beyond the standard. Correct me if I'm wrong, but what we have in flat space is states, \[ |\psi> \]...
  48. H

    Decibels, pressure & displacement amplitudes

    Homework Statement A jackhammer emits sound at a decibel level of 130 dB. The wavelength of the sound is 1.0 m. What is the linear sound intensity? What is the pressure amplitude? What is the displacement amplitude? Homework Equations Beta = 10 log (I / Io) ...and?? The Attempt...
  49. R

    Different subsidiary notes with varying amplitudes

    Homework Statement 1. Two identical guitars are played by two persons to give notes of the same pitch. Will they differ in quality? Give a reason. 2. How do you account for the fact that 2 string instruments can be used to give notes of the same pitch and loudness but different quality...
  50. S

    Transition amplitudes and relation between wavefunctions

    bb] The dipole transition amplitude for the transition (nlm) -> (n'l'm') is given by [/b] \int \psi_{n'l'm'}^* \vec{r} \psi_{nlm} d\tau Is the dipole transition amplitude simply a measure of how likely a certain transiton is?? Heres another question In converting \psi_{nlm_{l}m_{s}} =...
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