Frequency Definition and 1000 Threads

Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as temporal frequency to emphasize the contrast to spatial frequency, and ordinary frequency to emphasize the contrast to angular frequency. Frequency is measured in hertz (Hz) which is equal to one event per second. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute (2 hertz), its period, T—the time interval between beats—is half a second (60 seconds divided by 120 beats). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

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  1. J

    Frequency and Sound Wave Reflection

    I got that the sound wave will take 0.3s between the student and the left wall. It takes 0.5s between the student and the right wall. The first time these waves will coincide is 1.5s (5 trips for left side and 3 for right side). I then did 1/1.5 to get 0.67Hz. However, the answer is 6.67Hz. I'm...
  2. K

    Doppler effect and beat frequency

    Summary:: Two speakers A and B are at rest, and a listener L stays on the line that connects the two speakers (see picture). The speakers have almost the same frequency. Assume that the speed of sound in air is 340 m/s. When the listener is at rest, he/she hears beats with frequency 6 Hz. The...
  3. M

    Frequency Shift Key Modulation: how are the carrier frequencies chosen

    Question: For frequency shift key modulation in the binary case, how are the two carrier frequencies chosen? From online reading, I have seen that the carriers are chosen to be different but also with the goal of minimising bandwidth and without any overlaps of the spectra, etc. However, I...
  4. QuasarBoy543298

    A Why does a photon have a defined frequency but is also somewhat localized?

    a photon have defined frequency , but we treat it as a localized particle ,how that can be? if i am looking at second quantisation, photons are modes of the electromagnetic field , and they are not localized at all , but we do know that photons are somewhat localized , like in the...
  5. Lnewqban

    Study about high frequency mosquito flight

    Please see article here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5412966/?report=classic
  6. L

    I Converting "Luminosity per unit wavelength" to "Luminosity per unit frequency"

    If there is a luminosity per unit wavelength defined as L_λ dλ, am I correct in thinking that the conversion to luminosity per unit frequency (L_ν) would be L_ν = L_λ (λ^2/c)? And building off of that, if the shape of a spectrum was proportional to a power-law: L_λ = λ^(β), is there a way to...
  7. A

    B Photon Frequency: How Special Relativity Affects Light

    How can a photon have a frequency? Anything moving at the speed of light is predicted to have a zero time rate, e.g. the frequency of a ticking clock would be zero. So no aspect of the light should change along its path - in the same way that no aspect of the moving clock would change. If...
  8. fisher garry

    Frequency in Maxwell's equations

    $$\textbf{F} \cdot d\textbf{l}=q(\textbf{E}+\textbf{v} \times \textbf{B})\cdot \textbf{v} dt$$ If we denote $$q=\rho d \tau$$ and $$\rho \textbf{v}=\textbf{J}$$ $$\frac{dW}{dt}=\int_{V} (\textbf{E} \cdot \textbf{J}) d \tau.$$ From maxwell law's $$\textbf{E} \cdot \textbf{J}=\frac{1}{\mu _0}...
  9. E

    Calculating Wave Amplitude and Frequency

    My attempts were these, a) 2.0% / cycle * 25 cycles = 50% So, I got half of the first amplitude which is 0.5 m (seems not right though...) b) w=2pi/T , so put 0.5 at T, I got w=12.6 cycle/sec 12.6 cycle / sec * 6.3 sec = 79.2 cycles and it is obviously not right to me... May I get...
  10. Nathan M

    Understanding frequency calculations of an object (e.g human body)

    Apologies for the noob question. The frequency of the human body can be calculated based on weins law as follows: Wavelength = 0.002898/310 = 0.00000934838 m Plugging this into the equation λν = c we get frequency = 299792458 / 0.00000934838 = 32069 Ghz Elsewhere, I see that the resonant...
  11. P

    Frequency of sound received by an observer

    My thought process was this, They are asking us to find the frequency of sound received by observer when the source reaches at origin. According to me when the source reaches origin there would be no component of source's velocity in the direction of observer, hence vs=0 vo=0 since the observer...
  12. B

    What is the resultant frequency if two similar waves superpose?

    for a) I have ##v = \lambda f= \frac{\omega \lambda}{2 \pi}## for c) and d) I denote ##\frac{2\pi}{\lambda_1} = k_1## and ##\frac{2\pi}{\lambda_2} = k_2## assuming ##k_1 > k_2##. so using the triangular identity I got $$y_1 + y_2 = 2A cos(\frac{k_1+k_2}{2} x - \frac{\omega_1 + \omega_2}{2} t)...
  13. C

    Frequency of EM waves produced by linearly accelerating charges

    I was wondering about EM waves produced by linearly accelerating charges, as opposed to oscillating charges. With oscillating charges, the frequency of the wave depends on the frequency of the oscillation of the charge. But what determines the frequency of the wave produced by a linearly...
  14. F

    Why does the amount of Refraction depend on wavelength?

    I understand that electrons of a material have a natural frequency of vibration and the refractive index results from the phase difference between the incident light's field oscillations and the field oscillations of these electrons...
  15. N

    High Frequency Linear Array BeamForming

    Hi all I am doing some research on High Frequency Linear Array beam forming (for imaging sonar). For that purpose, a linear Rx Array of 100 channels have been constructed with inter channel spacing of 14.3mm. A transmitting Tx probe operating at 420 KHz (approx. 300 cycles CW pulse) is placed...
  16. E

    Impedances for RLC circuits in the limit of zero frequency

    If a voltage source is sinusoidal, then we can introduce a phasor map and come up with equations like$$V_0 e^{i \omega t} = I(R + i\omega L + \frac{1}{\omega C} i)$$where ##I## would also differ from ##V## by a complex phase. But if you set ##\omega = 0##, which would appear to correspond to...
  17. Abdullah Almosalami

    Intuitive Explanation of Mass-on-Spring Oscillator Frequency

    I just noticed something that is a little bit of a different perspective on a mass-on-spring (horizontal) simple (so undamped) oscillator's frequency and looking for some intuition on it. There are many ways to derive that for a mass on a horizontal frictionless surface on a spring with spring...
  18. M

    A Eigenvalue problem: locating complex eigenvalues via frequency scan

    Hi PF! Here's an ODE (for now let's not worry about the solutions, as A LOT of preceding work went into reducing the PDEs and BCs to this BVP): $$\lambda^2\phi-0.1 i\lambda\phi''-\phi'''=0$$ which admits analytic eigenvalues $$\lambda =-2.47433 + 0.17337 I, 2.47433 + 0.17337 I, -10.5087 +...
  19. agnimusayoti

    Finding the Fundamental Frequency of a Combination: Boas's Method

    This problem came from Problems, Section 3 Chapter 7 in ML Boas, Mathematical Methods in Physical Sciences. Boas suggested to make a computer plot. From my computer plot (I use online graphing calculator) and find that the period of the sum is 2. Instead of using computer, I want to find the...
  20. H

    Effect of initial stress on the natural frequency of vibration

    Hello all, We might have observed that by tightening a string of a musical instrument, the natural frequency of the string changes. But I can not describe this phenomenon by the theory of linear elasticity. Also if we simulate the vibration of a bar with the help of structural software tools...
  21. A

    Specific Absorption Rate(SAR) - caused from radio frequency from mobile phones

    Why SAR value at body is allways higher than at head?
  22. handyman123

    Not able to get the desired output frequency using a Wein Bridge Oscillator

    Can anyone help me find what is wrong in this circuit? given, slew rate of the op amp is 400V/us and max output current for opamp is 40mA but the opamp is lm741.
  23. PainterGuy

    Tuning fork frequency equation

    Hi, I was trying to see how the frequency equation for a tuning fork is derived. It looks like it's based on the equation of cantilevered beam. In other words, I'd say that historically the equation for a tuning fork was derived somewhat in a similar fashion as was done for a cantilevered beam...
  24. TytoAlba95

    Biology What is the genotype with lowest frequency?

  25. F

    Total Energy, Period and frequency of a masspoint

  26. therealist

    How do I find the frequency, speed and direction of a wave

    Hey I am trying to learn how waves move in time and I am not sure how to solve the following question. Can someone please guide me through it.
  27. M

    I Error on a transition frequency

    Hello! I am really new to this field, so I am sorry if my questions is silly or missing some parts. Please correct me if that is so. I am a bit confused about how well we can extract the value of a transition, say from ground to an excited state, of an atom (let's assume we can ignore any other...
  28. A

    B Mechanical Resonance and Natural Frequency at the Atomic/Lattice Level

    How do we explain resonance of a complex system (say a bridge) at the atomic level? What's happening to its molecules when it's oscillating at resonance, and does that have anything to do with the frequency at which the molecules oscillate in the material?
  29. Arunsaikalki

    What is the natural frequency of this system?

  30. stanley

    Impact of frequency on Faraday cages

    I've been reading about faraday cages. The way I see, it works because the condutor will separate the charges so that the eletric charge inside is 0. Then I saw a lecture in which the professor was carrying a radio and the signal stopped as soon as he entered the cage however we were still able...
  31. Tymofei

    Influence of initial shift on undamped frictionless forced oscillations

    I have general equation for undamped forced oscillations (no friction) which is: I just wonder about,what type of motion should occur when initial conditions are both 0 (i.e v0=0 and x0=0). My intuitive expectation is that as there is no 'natural' oscillations at beginning,vibration has to be...
  32. M

    Calculating frequency of sin(x)

    Greetings, I'm confused about calculating frequency of sin(x) function. Applying basic equations I get this: T= 2pi f = 1/T = 1/(2pi) = 1/6.28 = 0.15923 Hz I know it's wrong, but what am I missing? Also, how can the period be in radians, I always thought that T should be in seconds.
  33. Tony Hau

    How to derive the frequency for two body oscillatory motion

    Here is the diagram of the problem: and here is the answer of the question: What I don't understand is equation 1 and 2. The Hook's law states that F = -k(change in x) Why the change in x1 equals to x1-x2+l? x1-x2 equals to the length of the compressed spring. I cannot convince myself that...
  34. J

    Calculate work, frequency and Plank's constant

    i. the threshold frequency; 3.9x10^14hz? it appears the line intersects at 3.9ii. the work function of the surface; 6.626x10^-34x3.9x10^14= 2.58414 × 10^-19J iii. Planck's constant unsure
  35. M

    Control Theory - Nyquist Plot - Speed of Response from Low Frequency Asymptote

    [Moderator: moved from a homework forum. This does not sound like homework.]Homework Statement:: Why is it the case that when the low-frequency response is to the right of the M = 1 line that the 'speed of response is slow'? Relevant Equations:: M-cirlces Hi, Hope you are doing well and...
  36. Tony Hau

    Angular frequency of a damped oscillator

    So in my textbook on oscillations, it says that angular frequency can be defined for a damped oscillator. The formula is given by: Angular Frequency = 2π/(2T), where T is the time between adjacent zero x-axis crossings. In this case, the angular frequency has meaning for a given time period...
  37. S

    I Uncovering the Mystery of Lunar Perigee Frequency | 2020 Insights

    Hello- I was looking at a table of the dates of lunar perigees for 2020, and I noticed that most of the perigees were between 27 and 29 days apart. So the perigees do not appear at a constant frequency, which I did not expect. There are even a pair, between June 30 and July 25, which are...
  38. B

    Second highest frequency in a sound pipe

    So here is my question Have tried it and got these as my answers Have I done part b) correctly over here to find the 2nd highest frequency? Any help would be much appreciated! Thanks
  39. B

    Frequency of TV signal from EM waves

    Having some trouble with this question I believe phenomenon behind this one is that the student is passing between nodes (minimum displacement) to antinodes (maximum displacement) which explains why the signal weakens and strengthens continuously. Hence the ans to this is option C? For the...
  40. 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...
  41. J

    A Electron frequency components during orbital tunneling

    For example, we have this two potencial wells approaching, the electron is confined in one. the final appearance will be like this: THEN, if we know a wave packet is formed by many frequencies, but in a potencial well there are just few frequencies allowed, energy levels, so let's say, one...
  42. Deepesh

    Does Increasing Mass Affect the Natural Frequency of Vibration?

    My query here is, Suppose there is a 2 kg mass To oscillate it/vibrate it, it will take some force and it will have some natural frequency Now I increase the mass to 5 kg so to vibrate it, won't it take more force and so at the end, won't the natural frequency of the object increase? as its more...
  43. A

    Motor / transformer variable frequency control

    few questions 1) is it true that for a 50 or 60hz induction motor maximum torque is achieved from 0hz up to design hz and if an VFD is used and frequency is increased above 50 or 60hz like 100hz the rpm will increase but the available torque will decrease? Is the reason behind this the fact...
  44. greg_rack

    How to link frequency and speed? Doppler effect

    I had many attempts on trying to solve this one, but I got always stuck in the problem-solving part: how do I manage to find the source-speed from the Doppler formula, in an analytical way, and then reach to the result-formula? Anyway, I'm pretty sure the only formula needed to solve this...
  45. 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...
  46. S

    Is the tuba an open or closed pipe?

    Is tuba open or closed tube? I google the picture of tuba and I think it is closed tube (one end open to air and one end put into mouth so it becomes closed end). Using formula of closed pipe, I get f = 24.5 Hz but the answer is 49 Hz which is obtained by using formula of open pipe. How to...
  47. D

    Can a Coiled Antenna Receive Radio Signals at 30 MHz?

    if an antenna 8.2 feet long was coiled up into a coil could it still receive radio signals at 30 megahertz?
  48. 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...
  49. M

    Oscillation frequency of 2D circular drop in an ambient environment

    Hi PF! Do you know what the natural oscillating frequencies are for a 2D circular drop of liquid in an ambient environment (negligible effects)? Prosperetti 1979 predicts the frequencies for both a spherical drop and bubble here at equations 5b and 6b. There must be a simpler circular 2D...
  50. Saptarshi Sarkar

    What happens when the frequency of AC is very high?

    If I consider a wire carrying AC current, I know that at an AC frequency of 0Hz, the current will always in the same direction. If I change the frequency to 1Hz, the current will flow left to right for 1 second and then right to left for 1 second. I guessed that at these higher frequencies, as...
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