What is Frequency: Definition and 1000 Discussions

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. V

    Same frequency sounding different

    I was always thinking that frequency decides the type of sound we hear ( ex: high pitched squeaky sound). But then I read somewhere that loudness i.e. intensity can also affect the sound we hear. Still the quality of sound should depend only on frequency since loudness would simply make it more...
  2. penguin46

    Frequency of Oscillations of a Bead Resting on a Gas

    Hi, this is a question from my textbook that I can't quite make sense of. I don't really know where even to begin, to be honest. The only thing I can think of is that the bead is at equilibrium, thus the force of gravity is equal to the pressure exerted by the gas. I don't know where the heat...
  3. A

    Inverting op amp frequency response Bode plot help

    Using analog discovery 2 kit and the bode plot produced by the network analyzer is off. The scope looks fine and everything is behaving how it should except for the bode plot. The magnitude of the bode plot will start at the correct dB then right before tapering off it shoots up a few dB and...
  4. D

    I Frequency of EM waves in classical and quantum physics

    in classical physics, when a charged particle oscillates, it emits an electromagnetic wave, and the frequency of the wave depends on the frequency with which the particle oscillates. But in quantum physics, when an excited atom emits a photon, the energy of the photon depends on the magnitude of...
  5. B

    I Resonant Frequency Formula for a given object

    I know the v = λf is the formula to find the resonance frequency of a single continuous wave and the formula for resonance frequency of a spring is: 1/2π∗sqrt(𝑘/𝑚) but what about the Formula for a random object? a car, or a rock, water ? is there one Formula to rule them all? or do you...
  6. S

    Finding the frequency of a string based on Mass and Tension

    I saw the following problem in a test I was reviewing: I don't understand how they got their answer. I used the formula: ƒ=sqrt(T / u) / 2L where f is the frequency of the string, T is the tension, u is the linear mass density, and L is the length of the string. I got: T = mg = 50 * 9.8 = 490N...
  7. J

    Can Resistance Determine the Torque in a Solenoid Pendulum System?

    The flux enclosed by the loop consisting of the solenoid, wires and conducting rod at an angle θ is Φ = blBsinθ, then using small angle approximations and differentiating the induced emf can be found. I know that there must be some torque opposing the motion but am unsure how to proceed.
  8. D

    I Time & Gravity in Rotating Faster Than Light?

    If a person was rotating on a verticle axis from head to toe like the Earth or quasar. If nothing can go faster than light, from the person's perspective looking at the stars traveling across the night sky, if you increase the rotation of the earth, stars further than a certain critical distance...
  9. E

    Effect of temperature on vibrational frequency of a violin string

    Variables: Dependent: Vibrational frequency of violin string (Measured using mobile tuning app) Independent: Temperature in which string is plucked (Measured using infrared thermometer) Controlled: Violin String, Tension of violin string, Length of violin string, Method of plucking...
  10. Moondog

    Fog Droplet Size as a function of Ultrasound Frequency

    I need to know how to predict particle size of a water driplet produced by a given ultrasonic frequency? For example, an ultrasonic fogger will create ~5 micron water driplets at a frequency of 1.75 MHz. I do know that the higher the frequency the smaller the driplet diameter. How is this...
  11. mishima

    Finding Piezoelectric Crystal Frequency for Coherer experiment?

    Hi there, I've been fascinated by using simple coherers to pick up the electromagnetic signal from a spark (in imitation of early radio experiments, for high school education). I am using a push button ignitor (piezoelectric crystal) attached to a simple dipole antenna for the transmitter. When...
  12. Tobias Holm

    Find frequency such that two components have same average power

    (This is my first time posting here, sorry in advance for any difficulties. ) All componenets of same type has same magnitude, so e.g. the two resistors both have $R$ resistance. Given the difficulty of the previous exercises, I believe I'm over complicating the problem. However, here is what...
  13. Z

    A Can a Solid Vibrate at Debye Max Frequency?

    Can a solid vibrate with only one frequency-Debye maximal frequency?
  14. B

    B Is the highest frequency possible the inverse of Planck time?

    Is the highest frequency possible the inverse of Planck time? Separate or connected question, what's the highest frequency achievable practically today?
  15. PainterGuy

    Signals with the same frequency spectrums but different power levels

    Hi, I understand that if there are two signals whose spectrums consist of different set of frequencies, they can be separated using a filter such as bandpass filter on the receiver end. Is it possible to separate two signals who frequency spectrums are the same but power levels are different?
  16. L

    At what frequency can Planck's law be used to determine the temperature?

    Hi, I am not quite sure if I have calculated the homework correctly :-) I proceeded in such a way that I first calculated from which frequency the two terms are equal, and thus the equation results in zero. Then I figured a relative accuracy of 10% equals a relative error of 90%. So I...
  17. P

    I What is the role of frequency in music?

    Setting aside pure sine waves, and looking instead at real-world sound, such as music, I wonder what "frequency" is? Fourier's Theorem seems to be aimed specifically at PERIODIC waveforms, but music (as just one example of real-world sound) is not periodic, as far as I can see. So it is not...
  18. C

    Resultant Frequency and Wavelength of Interfering Sound Waves

    ##-w1## and ##-w2## are to shift the cosine graph to the right, and ##\frac{2pi}{\lambda}## is to stretch the graph. But I can't seem to draw an appropriate ##y1+y2## graph (quite irregular) and I struggle to find the resultant frequency and wavelength. Also, why is there angular frequency in a...
  19. P

    LTSpice functionalities regarding its Frequency Domain Analysis

    The time domain analysis is easier to plot compared to analyzing the frequency with respect to the phase. But, LTSpice makes it look really easy. So, for a small signal AC analysis, LTSpice does use a AC voltage source for its frequency domain analysis function. This must be a really convenient...
  20. S

    Amplitude of standing wave for higher frequency

    I understand the part where there will be more nodes produced because number of wave produced will increase (let say from half wave to one wave). But I don't understand the part where the amplitude will be less. How can number of nodes (or frequency) affect the amplitude of standing wave...
  21. A

    Understanding CPU Frequency Waveforms and Dead Time in Modern Processors

    There was a thread recently in another subforums where a user talked about creating "square waves" at Ghz frequencies. It was said there that at that frequency range one cannot have a square wave as the inductance "rounds off" the edges making the waveform sine like. I am wondering then how...
  22. MisterH

    A Minimum sample length to estimate the frequency of a sinusoid

    Given a discretely sampled horizontal sinusoid of length p, and unknown amplitude, what is the minimal number of consecutive points on a window that is required to correctly estimate its total length, starting at any random point on the wave? Initially I would think it would be either p (full...
  23. A

    Klystron beam current, drive frequency, LHC CW example

    First of all I want to ask , do the LHC power klystrons work always in CW or are their frequency shifted to correct for timing of the bunches in the LHC tubes in case something isn't aligned or doesn't that ever happen? Also how do they drive the klystrons at LHC or other CW operation from an...
  24. S

    Adding two sinusoidal waves of same frequency but out of phase

    Asin(wt)}+Bsin(wt+a) Asin(wt) +B sin(wt)cos(a) +Bcos(wt)sin(a) Asin(wt) + ksin(wt) + Lcos( wt) (A+K) sin(wt) + Lcos(wt) Fsin(wt) + Lcos(wt)
  25. Haorong Wu

    I Understanding Frequency in Rindler Coordinates for a Scalar Massless Field

    I consider a scalar massless field obeying the Klein-Gordon equation ##\Box \psi=0 ##. First, in Minkowski spacetime, a solution of the equation is $$ u_{\mathbf k}(x^\mu)=((2\pi)^3 2 \omega)^{-1/2} e^{ik_\mu x^\mu}$$ where ##\mathbf k=(\omega, \vec k)##. So this mode has a frequency of...
  26. Peter J Carroll

    I Quantum spin, wavelength and frequency

    Greetings, I'm new here, I have an interest in the nature of reality, and a question. Does the quantum spin of a particle (its intrinsic angular momentum) have anything to do with its wavelength and frequency? One of the experts on Quora said no, and I cannot find anything about it on the web...
  27. person123

    I Water Waves Over Obstacles: Higher Frequencies Grow, Not Decay

    In general, it seems that higher frequencies of a wave dissipate more than lower frequencies. For sound waves, it explains why you can hear lower pitches from farther away. For a vibrating string or plate, the higher frequencies also dissipate first, with the fundamental fading last. For water...
  28. I

    Cutoff frequency for this RLC circuit

    How would i find the cut of frequency of this RLC circuit .I have used LTspice to find it but what is the equation for finding it
  29. S

    Minimum Frequency of FM Data / Catastrophic Error Scenario?

    Ever since I learned about FM something's been bugging me, which is that the PLL error correction acts on the encoded data, seeming to leave open the possibility of the shape of the data itself interfering with the PLL's interpretation of what the carrier frequency is. It seems dangerous to mix...
  30. S

    Finding frequency of microwaves

    I thought 14 mm, 86 mm, 156 mm, 225 mm and 293 mm are the position where constructive interference happens 14 mm is the position of 1st maxima, 86 mm is the position of 2nd maxima and etc (measured from a certain position of center maxima) But when I used that numbers to calculate the fringe...
  31. I

    Engineering Frequency Response Between 100Hz and 100kHz

    So am trying to find the Frequency response of a RC LPF between frequencies 100Hz-100kHz ,but i don't know what formula to use .
  32. D

    I Is there a way to calculate the frequency of an electron wave?

    According to de Broglie, the wavelength of an electron wave is L=h/p. Is there a way to calculate the frequency of such a wave? Thank you!
  33. B

    Trouble with Plasma Frequency Calculation

    This would appear to be a straightforward algebra problem, but it just doesn't pass the smell test for me. The issue might be with the number of electrons per cubic meter, as that was calculated in a previous problem, so let me know if that number seems wrong. My plasma frequency (##\nu##) not...
  34. J

    Why is the sinusoidal considered the fundamental frequency?

    What property of a sinusoid makes it so special? I understand Fourier analysis, but really you could do Fourier using any periodic function as the building block. Sinusoids really do seem to be fundamental though, if you narrow the pass band of a filter with any random signal you will get a...
  35. tworitdash

    MATLAB Creating and recovering a frequency shift in time domain in MATLAB

    I am trying to simulate and process the Doppler signals. My main problem is a little more complex so I am only posting a simple version of it. Task1: I have a time-domain signal with the velocity of the target as mu. I need to change the velocity to mu cos(theta) where theta is a vector from 0...
  36. A

    Photon-photon interaction, EM frequency overlap

    Now from physics I read that photons don't interact with one another normally, at higher energies they might through pair production but that is besides this point. So this means that for example if we have multiple sources of EM radiation like say multiple sub pixels within a screen then each...
  37. G

    Area Under Frequency versus Time Curve meaning?

    Hello: Let's say you have a string and get data by changing the frequency a transverse wave in the string to get different standing modes. You measure the wavelength of each mode for each frequency. That is, the data you get are frequency and wavelength. Now, you are trying to find the...
  38. P

    Can someone give me a better intuition of bandwidth?

    Can someone give me a better intuition of bandwidth. The way I see it, is that the bandwidth is the range of frequencies which a signal/wave is allowed to have. This doesn't feel complete though. For example, how can I explain that TDMA, FDMA and CDMA are similar in this sense. As far as I know...
  39. S

    Frequency of boundary layer instability

    I've been searching the net but can not find any freely available literature. Can someone give me a quick lesson on boundary layer instability and its frequencies? I have an equation that claims to scale the instability frequency by: F = U/2*delta U is leading edge velocity delta is layer...
  40. H

    Exploring Current, Voltage & Z When Frequency Increases

    https://www.physicsforums.com/attachments/6-png.282284/?hash=0362cb24c9a8ed9b3ee9efab56a28e3d If the increasing frequency leads the current amplitude to increases, then Z decreases because V = I*Z and V remains unchanged...
  41. M

    Minimum Tone Spacing: Coherent Frequency Shift Keying

    Hi, I was reading through some online notes and was wondering: when dealing with coherent FSK, what is the minimum tone spacing and why? I know that for non-coherent FSK, we can show that the minimum is: ## f_1 - f_0 = \frac{1}{T} ## where ## T ## is the symbol period. However, if we are now...
  42. tworitdash

    MATLAB FFT of conjugate doesn't coincide exactly at the negative frequency

    I am trying to understand why the conjugate of a signal in the time domain doesn't produce an exact flip of the frequency domain spectrum. There is always a one-pixel shift in the result. The MATLAB code is shown below. I use a flip for the conjugate spectrum to show that it doesn't match the...
  43. H

    Magnetic Field & Frequency: Exploring the Relationship

    https://www.physicsforums.com/attachments/282201 Are we using this equation above to explain this question? The magnetic field is definitely in sinusoidal form but how does it proportional to the frequency of the source?
  44. M

    Digital Filters: why is sampling frequency equal to 2*pi unit circle

    Hi, I was working through a filter design problem and got stuck on a concept. Scenario: Let us say we have the following pulse transfer function and the sampling frequency is ## f_s = 50 \text{Hz} ##. G(z) = \frac{1}{3} \left( 1 + z^{-1} + z^{-2} \right) The zeros of the transfer function...
  45. H

    Angular Frequency of a two-object system

    I calculate as follow and get a correct answer, but I wonder why the weight of the ladder 6 kg is not included in the mass (m) in the numerator. w= √(mgd/I) = √ { (42*10*1)/ [(1/12)(6)(2^2)+42*1] } = √ (420/44) = 3.06
  46. H

    What is the angular frequency of oscillation?

    ω^2 - (ωo)^2 = 2 (-630) (0.32) = -403.2 This is what I have now and I stuck here.
  47. tworitdash

    MATLAB How to change the frequency values inside a time domain signal phase

    The problem I am having is simple. I have a Gaussian spectrum initially. Like this, Process 1: S = m0/sqrt(2*pi*sigma^2) * exp(-(vel_axis - mu).^2/(2*sigma^2)); Here, mu is the mean velocity (frequency) and sigma is the standard deviation. vel_axis is the axis on which I am calculating this...
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