What is Frequencies: Definition and 411 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. H

    Digital Electronics: Image Frequencies & Nyquist/Shannon Theorems

    In digital electronics -- and notably digital reconstruction filters, Shannon and Nyquist theorems -- one encounters "images" (or frequency images). In digital audio, for example, after the DAC (digital-to-analog converter), one must filter the output of the DAC with an anti-imaging filter...
  2. W

    Combining High and Low Pass Filters

    Homework Statement Suppose we have a noisy signal (superposition of many frequencies), but we are only concerned with a particular part of the signal within the noise at a frequency f(desired) = 1 GHz. In a sentence or two, explain how you could isolate the desired part of the signal by using...
  3. A

    Frequencies of fundamental standing waves

    Homework Statement Homework Equations Harmonics equations The Attempt at a Solution So, I got (A), which is the answer key is correct, but I'm not sure whether my reasoning is right or not. Would this be considered a closed-end air column question? Anyways, according to the length-wavelength...
  4. M

    Question on corner and resonant frequencies

    Homework Statement 1. An RC filter is constructed by modifying a voltage divider. The top resistor R1 = 3kOhms remains the same but the bottom resistor R2 is replaced by a capacitor C = 8nFarads. Determine the corner frequency fc for this filter in kHertz. 2. For an RLC circuit R = 12.4...
  5. Const@ntine

    Tuning a Violin's Chord (Frequencies)

    Homework Statement A violin's chord has a length of 0.350 meters, and is tuned to the sound of the note Sol, with a frequency of fG = 392 Hz. a) How far from the edge of the chord does the violinist need to place his hand, in order to play a note La, with a frequency of fA= 440 Hz? b) If...
  6. L

    Methods for Damping High Frequencies in FEM Thin Film Model?

    I would like to simulate the vibrations of a thin film polymer in vacuum using nonlinear analysis. For this purpose I am using an FEM program I have written in MATLAB. I do not have any data regarding damping in the structure, so I am estimating the damping using stiffness-proportional-only...
  7. M

    I Modal frequencies of a vibrating circular membrane? (DRUM)

    I am in the process of trying to develop a modal drum synth. I have the following graphics as references for the frequencies of some of the first modes relative to the fundamental: This is a good start. But I want to be able to model more modes than just that. What is the formula required...
  8. W

    Flute player initial frequency?

    Homework Statement A flute player hears four beats per second when she compares her note to a 587 Hz tuning fork (the note D). She can match the frequency of the tuning fork by pulling out the "tuning joint" to lengthen her flute slightly. What was her initial frequency? Homework Equations Not...
  9. R

    Phase relationship at high frequencies

    Homework Statement Given the transfer function: Find the phase relationship between the input and output voltage at high frequencies Homework Equations NA The Attempt at a Solution My approach was to find the phase of the transfer function, which I got to be: I assumed that "very high...
  10. Andre Teixeira

    I How to obtain the resonance frequencies of a given material?

    The frequency of plasma already achieved ... in a study, is presented the resonance frequency in eV, how to obtain in Hz? Wo = 7eV
  11. T

    Resonance at low and high frequencies of 2 closed end tubes

    Homework Statement The figure (attached) shows two tubes that are identical except for their slightly different lengths. Both tubes have one open end and one closed end. A speaker connected to a variable frequency generator is placed in front of the tubes, as shown. Te speaker is set to produce...
  12. G

    Current at Extreme Frequencies

    A work colleague of mine told me that if you have an AC voltage across a wire and the frequency is high enough, there would not be any current, because electrons don't have time to move from one atom from another. Is there any truth behind this?
  13. 1

    Help finding the vibrational frequencies and normal modes

    Homework Statement Let's say that I have a potential ##U(x) = \beta (x^2-\alpha ^2)^2## with minima at ##x=\pm \alpha##. I need to find the normal modes and vibrational frequencies. How do I do this? Homework Equations ##U(x) = \beta (x^2-\alpha ^2)^2## ##F=-kx=-m\omega ^2 x## ##\omega =...
  14. L

    Find two lowest frequencies standing wave

    Homework Statement A metal bar is attached into a vice in the middle. Bar is hit with a hammer creating a longitudinal standing wave find the two lowest frequencies. Bar's length l= 3m wave velocity = 5100m/s Homework Equations wave equation ## v = \lambda * f ## The Attempt at a Solution...
  15. T

    Can we get Higher Frequencies from an Oven Magnetron?

    Is it possible, and if so, how should we modify a typical oven magnetron so as to produce higher frequencies of EM radiation?
  16. N

    I Can a Single Speaker Direct Low Frequencies? Exploring Options and Limitations

    Hey everyone. I have a couple of questions in regards to the direction of sound. I am wanting to direct lower frequencies (30-60Hz). When I say direct, I mean more of a beam rather than radiating out from the front of the speaker in all directions like a traditional wave. I have been looking at...
  17. M

    Quantum Oscillator with different frequencies

    Homework Statement Solve the Schrödinger Equation for an harmonic potential of the form (1/2)m\omega_+^2x^2 for x>0 and (1/2)m\omega_-^2x^2 for x<0. Find the equation that determines the energy spectrum. You can use m=1/2 and \hbar=1 Homework Equations [/B] I wrote down Schrödinger Equation...
  18. D

    How can you measure frequencies in the human body?

    I read posts from a few years ago regarding measuring frequencies in the human body. I am wondering if there are any new developments. What devices can measure frequency? Thanks!
  19. Cool4Kat

    How did they hear small wavelengths (high frequencies) *before* superheterodyne?

    Hi, I am researching the early history of electricity and I would love some help. So, in the very early 1900s (like 1906) there were several items created that were diodes (crystals, Fleming valve, electrolytic detector). As far as I understand, people would use these diodes to convert the AC...
  20. M

    Kerr Diagrams for Defect Frequencies

    I am currently undertaking a module in Failure Analysis, one topic of which is vibration monitoring of bearings. During this study, the notion of first and second Kerr diagrams as a tool for analysis came up. I have been trying to find additional information on Kerr diagrams; however, outwith...
  21. S

    Frequencies -- what is the average frequency for the human body?

    Hi all, Would anyone be able to let me know what the average frequency is for the human body? Also, what is the average frequency of a home? What would be considered abnormal? According to the Ofcom UK Frequency Allocation Table it notes different frequency uses e.g. a frequency of 1,600...
  22. Luke Frederiks

    Calculating frequencies with the Doppler Effect

    Homework Statement A train moves at a constant speed of v = 25.0 m/s toward the intersection shown in Figure P13.71b. A car is stopped near the crossing, 30.0 m from the tracks. The train’s horn emits a frequency of 500 Hz when the train is 40.0 m from the intersection. (a) What is the...
  23. S

    Hardware that can produce sound waves with frequencs 0-200hz

    i'm doing an experiment to study the effect of sound waves on fire and smoke and would like to know how can i produce sound waves with frequencies varying from 0-200 hz
  24. M

    Resultant amplitude for waves of different frequencies?

    Homework Statement Two superimposing waves are represented by equations y1= 2sin 2π(10t – 0.4x) y2= 4sin 2π(20t – 0.8x) Find the ratio of Imax and Imin. Ans is (25:9) Homework EquationsThe Attempt at a Solution I know that intensity is proportional to the square of amplitude and maximum...
  25. Mohamed_Wael

    Determine the natural frequencies experimentally

    How can we determine the system properties (natural frequencies & damping ratio ) practically using forced vibration? One way is to measure the phase angle, using the bode plot, the exciting frequency corresponding to 90 (deg) phase shift should be the natural frequency, are there any other...
  26. Cloud Wolf

    A Determining molecular resonance frequencies

    I have been searching for ways to calculate resonance frequencies of complex molecules. I know that doing so is extremely complex, especially if that molecule contains many elements, but perhaps it could be feasible to target a specific component of a large molecule, such as a nucleus in a cell...
  27. U

    Understanding phase shift w/ time of 2 different frequencies

    Hi all, I hope this question is of an acceptable format to ask about here. I'm just having trouble trying to get a conceptual understanding of the following. I've been told that if I'm given two different frequencies that are completely in phase at time equal to zero, then I can find their...
  28. teetar

    Determining phase shift of two frequencies

    Homework Statement I'm given two frequencies: 4,000 Hz, and 5,000 Hz. They are completely in-shift at time ##t=0##. I am to find the time it takes them to get completely out of phase. Homework Equations The Attempt at a Solution I've not gotten waves very well thus far in physics. My teacher...
  29. I

    RLC Black box at different frequencies

    Supposed there is a black box connect to an AC circuit. Inside the black box, there are either a resistor connected with a capacitor or a resistor connected with a inductor. They can be connected either in series or in parallel. The total impedance and phase shift of the black box at 2 different...
  30. G

    Finding frequencies and wavelengths

    Hey! I'm struggling really badly with some physics homework, we've done nothing on this stuff in class and I can't find ANY help online and I'm stressing pretty bad right now so ANY help would be AMAZING! Here's my questions... "This question is about electromagnetic waves traveling in free...
  31. Tareq Naushad

    Which properties of photons carry info on size,width,height?

    I know when we see an object then the frequencies of photons reflected from the object carry the information about the colors. Frequencies of visible spectrum helps us to visualize colors. However which properties of photons help us to estimate distance,speed,size,width,height,depth, plainness...
  32. andrewkirk

    Acoustic 'beats' from mismatched musical frequencies - Comments

    andrewkirk submitted a new PF Insights post Acoustic 'beats' from mismatched musical frequencies Continue reading the Original PF Insights Post.
  33. D

    Why do sound waves with slightly different frequencies create beats?

    I have a question about 'beats' between two sound waves of slightly different frequencies. Basically, I think I understand everything on this page (and have read a few textbooks on this): http://www.animations.physics.unsw.edu.au/jw/beats.htm . And in practice, I work with this concept all the...
  34. AntonPannekoek

    I What is “normal” about normal frequencies and normal modes?

    So, my question is what does the "normal" part mean when one talks about normal frequencies and normal modes in coupled oscillations. Does it have to do with the normal coordinates that one uses when solving some problems, or with normal in the sense of orthogonal. Thanks for your help.
  35. nmbr28albert

    I Reflectance of metals at low frequencies

    When calculating the dielectric constant of metals using the Drude model, in the low frequency regime (infrared and beyond) one gets an approximately pure imaginary value: $$\epsilon(\omega) \approx i\frac{4\pi n e^2\tau}{m_e\omega}$$ which gives an absorption coefficient: $$\alpha(\omega)...
  36. T

    How do you compare the amplitudes of different frequencies?

    Hello everyone! I am in a pickle right now as I attempt to move forward in my research project on neurofeedback. I am trying to calculate the theta/beta ratio for individual subjects and then compare them statistically. The issue I am having is statistically comparing amplitudes of different...
  37. RicardoMP

    Normal Modes and Normal Frequencies

    Homework Statement I have to determine the frequencies of the normal modes of oscillation for the system I've uploaded.Homework Equations [/B] I determined the following differential equations for the coupled system: \ddot{x_A}+2(\omega_0^2+\tilde{\omega_0}^2)x_A-\omega_0^2x_B = 0...
  38. R

    MATLAB Fix Filtering Frequencies Code in Matlab w/o Built-In Filters

    I want to write a Matlab code which removes all frequency components from a .wav sound file except those within ##±25 Hz## of ##523 Hz## as well as its harmonics (up to the Nyquist frequency). I want to do this without using any built in filters. Here is my code so far: [s, Fs] =...
  39. R

    Identifying Fundamental Frequencies

    Homework Statement I have made a plot of a given .wav file in Matlab. The problem asks: find the fundamental frequencies of the 3 vibrating strings, and identify some of their harmonics. Homework Equations 3. The Attempt at a Solution [/B] So I made a Matlab plot of the power spectrum over...
  40. F

    Eigenvalues of a string with fixed ends and a mass in the middle

    Hi there. First of all, sorry for my bad english. I ´m trying to solve next exercise, from Vibrations and Waves in Continuos Mechanical Systems (Hagedorn, DasGupta): Determine the eigenfrequencies and mode-shapes of transverse vibration of a taut string with fixed ends and a discrete mass in the...
  41. G

    What is the Uncertainty of Human Hearing Frequency?

    what can be the uncertainty of the frequency that humans can hear ? I'm aware that there are many ways,but i tried google-ing to find them but i couldnt. if you could help me it would be great.
  42. steven george

    I Frequencies of standing waves in a straw

    I am a physics teacher and I my class is currently studying sound waves. I had my class make some noise makers with straws as shown here. http://www.physics.org/interact/physics-to-go/straw-oboes/ We measured the frequencies coming from the straws and they seem to act like a pipe open at...
  43. Hassan Raafat

    Calculating Half Power Frequencies in RLC Circuits

    at electric circuits , at RLC circuits , in case resonance :why do we calculate the frequencies w1 & w2 at half power frequencies ?
  44. henil

    Addition of Frequencies: Combining Same Phase, Different Amplitudes

    i want to add two frequencies having same phase but different amplitudes, in what manner i can proceed ?
  45. N

    Faraday cage, lower frequencies

    Faraday cages of the conducting type are not effective for lower frequencies; https://en.wikipedia.org/wiki/Electromagnetic_shielding#Magnetic_shielding mentions a frequency of 100 kHz. The electromagnetic spectrum is composed of both an electrical, and a perpendicular magnetic field. If a...
  46. E

    Light Frequencies: Exploring Properties & Speed

    I'm very curious about the properties of light I was hoping someone could enlighten me. Do all forms of light move at "Light Speed" or relatively the same. I was told that there are many "element combinations" could be made to "illuminate light" but not all forms of light share the same...
  47. M

    MHB Ratio of fundamental frequencies

    The 7th note has a frequency of L/3 and the 12th has a frequency of L/2. What is the ratio of the two frequencies? I feel like this is really easy but I don't know how to solve this.
  48. Y

    Nonlinear electric susceptibility and degenerate frequencies

    Hi there, I'm having a little trouble understanding the "distinguishability" of frequencies in the nonlinear electric susceptibility tensor. As far as I understand, if we have a SHG process with two collinear beams of the same polarization and frequency ω, there is only one susceptibility...
  49. N

    What causes the photon to move at different frequencies?

    What causes the photon to move at different frequencies? Thanks in advance
  50. Junichirol

    Matlab (calculate natural frequencies using eig function)

    Homework Statement Determine the corresponding natural frequencies M = [1 0 0 0;0 1 0 0;0 0 1 0;0 0 0 1]; C = [2 0 0 0;0 0 0 0;0 0 0 0; 0 0 0 0]; K = [10 -5 0 0;-5 10 -5 0;0 -5 10 -5;0 0 -5 10]; Homework Equations A = [zeros (4) eye(4); -M/K -M/C] [V,D] = eig(A) The Attempt at a Solution just...
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