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. fluidistic

    Characteristic vibration frequencies of a system

    Homework Statement I'm trying to solve an example in Boas's book (Mathematical methods in the physical science page 423) but by using Goldstein's (Classical mechanics) method. The mechanical system consists of 3 springs (with constants k) and 2 masses (with mass m) this way: |----m----m----|...
  2. R

    Natural frequencies and mode shapes

    Hi people, we were doing an experiment in lab where we excite a plate clamped at the circumference at various frequencies to detect natural frequencies. My questions are: 1. Sometimes at certain frequencies, we were observing multiple mode-shapes (an overlap of two mode shapes, to be exact)...
  3. R

    Wrong values for eigenvalues and frequencies

    Homework Statement I'm working on a problem that involves solving for the eigenvalues and the natural frequencies. I've attached my work as a pdf file and also the MATLAB code used to get the result. The problem that I'm running into is that the frequencies computed from the determinant are...
  4. S

    Change guitar string tension given two frequencies

    Homework Statement A particular guitar string is supposed to vibrate at 217 Hz, but it is measured to actually vibrate at 222 Hz. By what percentage should the tension in the string be changed to get the frequency to the correct value? Do not enter units. Homework Equations...
  5. A

    Interference fringe of light beams of different frequencies

    I have a question. If you have two light beams of different frequencies, would you observe interference fringes?
  6. S

    Resonance frequencies question (first and second resonance frequencies)

    Trying to figure out how to go about solving this question, using these forumlas i tried to solve it but i didnt get the right answers for frequency 1 i went with f1=v/2L for frequency 2 i went with f2=v/L any ideas on how to solve this?
  7. L

    Ultrasonic Frequencies: Harassment or Something Else?

    I understand it's possible to cross two ultrasonic frequencies one with sound modulating in it possibly in ssb format to recreate the original sound at the point the two cross. I think someone is using this trick to harass me. The sound appeared to be on the other side of a party wall at first...
  8. T

    SPEEDING TRAIN w/2 frequencies given while person is standing at rest. Please help.

    [b]1. A person standing close to a railroad crossing hears the whistle of an approaching train. He notes that the pitch of the whistle drops as the train passes by and moves away from the crossing. The frequency of the distant approaching whistle is 555 Hz; it drops to 472 Hz after the train is...
  9. I

    Amplitude of sum of waves with different frequencies

    Hi everybody, this is my first post here :P I'm currently struggling over a weird problem, which asks for the amplitude (eg, max value) of a sum of many waves with different frequencies. eg, max value of \sum_0^N {A_i cos(w_i t + \phi_t)}
  10. U

    Understanding Vibrations: Natural Modes and Frequencies

    Hi, I'm trying to understand vibrations and specifically what happens in the natural modes of frequency.. 1. It seems that the harmonic nature of solution(with Acos(wt)...where A is the amplitude) applies only in the natural mode of vibration...and so the system will have a defined mode...
  11. P

    Phase-Space desnsity and frequencies

    Alright, my previous thread on this I stated this question incorrectly and it was removed. Ok so I'll rephrase it and try and make it all spiffy so it follows the site's guidelines ;) I've looked up a lot of things in regards to phase-space, but I'm still a bit foggy on how it all works. I'm...
  12. T

    Inductance at high frequencies

    Hi All, I have a component that at 1 Khz has 100 mH Inductance and 100 Ω resistance. I know that at higher frequencies which I will need to run the circuit, these values won't be the same anymore. Is there any way, mathematically, to figure out what those values would be at higher...
  13. S

    Ionization resonant frequencies

    Is it true that by finding exact resonant frequency we could ionize matter or split molecules? What is frequency to split water molecules into H+ and HO- ions? What is resonant frequency to split up hydrogen atom into proton and electron? Would spliting water molecule require less energy...
  14. 1

    Why is this wrong? Wave frequencies

    Homework Statement Δp = (1.3 Pa) sin π[(3.00 m^-1)x - (300 s^-1)t]. Is the pressure of a wave. Find frequency Homework Equations The Attempt at a Solution Angular frequency = 300s^-1 = 300 hertz. Frequency = angular frequency / 2pi = 47.746 Someone, please explain...
  15. V

    Calculating Vacuum Fields at Different Frequencies

    How can we calculate the vacuum fields corresponding to certain frequencies?
  16. T

    Normal frequencies and normal modes of a multi-part system

    Homework Statement ***This is problem 11.29 in Taylor's Classical Mechanics*** A thin rod of length 2b and mass m is suspended by its two ends with two identical vertical springs (force constant k) that are attached to the horizontal ceiling. Assuming that the whole system is constrained to...
  17. K

    Medical Which frequencies does an MRI machine use? Is it microwaves?

    Hi, Which frequencies does an MRI machine use? Is it microwaves? Would prolonged exposure to it be damaging to the body?
  18. D

    Measure 2 magnetic fields operating at different frequencies?

    Hi, I have 2 coils arranged next to each other. One of them is used to generate alternating magnetic field at several Hz, and the other one also generate alternating magnetic field but at higher frequency (several kHz). Are there any magnetic sensors that can measure only the...
  19. T

    Problem with half power frequencies ?

    there is a parallel R - C circuit connected with a alternating current source of frequency 'w'. on plotting the function of |z| vs 'w' we get max at w=0; and max/2 at 'w'= 1/RC. while calculating power absorbed by resistor, we get Pmax = 1/2I^2R( >>>? how).. and at w = 1/RC power by resistor...
  20. L

    Finding length with two given frequencies

    Homework Statement You find an abandoned mine shaft and wish to measure its depth. Using an audio oscillator of variable frequency, you note that you can produce successive resonances at frequencies of 83.72 Hz and 107.64 Hz. What is the depth of the shaft? Assume the temperature in the...
  21. A

    Basic Harmonic Frequencies Question

    Homework Statement A string is stretched between fixed supports separated by 82.0 m. It is observed to have resonant frequencies of 334.000 and 389.667 Hz, and no other resonant frequencies between these two. A)What is the lowest resonant frequency of the string? B)What is the wave...
  22. V

    How to find parents' genotypes from progeny phenotype frequencies?

    Question: 8 phenotypes were observed as a result of a trihybrid cross. The frequencies of the phenotypes are a+ b+ c- = 570 a- b- c+ = 545 a+ b- c+ = 17 a- b+ c- = 20 a+ b- c- = 140 a- b+ c+ = 128 a+ b+ c+ = 65 a- b- c- = 61 No other information is given. It is not even specified if...
  23. J

    Finding Frequencies for Wave Sum Vanishing at x=0,L

    1. Homework Statement Write a wave in one space dimension as ARe(ei(kx-wt-d))where A is the amplitude of the wave. Find a second wave of the same frequency such that the sum of the two vanishes at x = 0 and x = L. Assuming the wave velocity c = w/|k| is fixed, for what frequencies ! is...
  24. E

    MIxed and reflected color frequencies.

    When I shine two different lights at a single spot on a white screen, say, yellow and blue, they both hit the spot and get reflected all mixed up and I see green. Thats all fine, but what is the actual structure of that reflected, in this case, green light? Is it a ordinary green photon with its...
  25. B

    How do musical frequencies relate to the numbers in this signal decomposition?

    My book reads step 1 = 2 cos(654πt)cos(-130πt) step 2 = 2 cos(2 * 327 * π * t)cos(130πt) step 3 = f2 - f1 = 392 - 262 = 130 Hz t = seconds π = pi I don't see how they get from step 1 to step 2, nor do I understand how they get from step 2 to step 3.
  26. E

    Why does a photon emit discrete frequencies of light?

    Why does an atom emit discrete frequencies of light? Solving the Schrodinger wave function for the hydrogen atom (that is a single particle representing an electron bound by a spherical potential) we find that it has discrete energy levels. Plotting every possible value of f in E'-E = \hbar f...
  27. P

    Uncertainty of room mode frequencies

    Hi - I'm new here - I'm just writing a paper based on an acoustical analysis of a rock/pop performance venue in a college I work at, and I'm up to my uncertainties section. I've read up on uncertainties, and feel confident in working out uncertainties for simple additions, multiplications...
  28. D

    Experiments regarding Soundwaves and Frequencies

    At high school currently doing a unit on sound waves and frequencies. Any suggestions on experiments/investigations we could look at. We have microphones, speakers, guitars, strobe lights... Any Suggestions?
  29. D

    Exploring Resonance and End Correction in Sound Pipes

    Our high school unit is looking at sound waves and frequencies and we are looking for some suggestions as to what experiments/investigations we could run? We have speakers, microphones, guitars, strobe lights pluss more to use, What are some ideas we could look at?
  30. D

    Can diff. EM frequencies create diff. magnetic fields with diff. properties ?

    ¿ Can diff. EM frequencies create diff. magnetic fields with diff. properties ? I understand that a magnetic field is generated via moving charged particles . Electricity and magnetism are linked through electromagnetism . Electromagnetism can be in different wavelengths and frequencies but...
  31. D

    Magnetic Frequencies: Exploring Electromagnetism

    ¿ Magnetic Frequencies ? I understand that a magnetic field is generated via moving charged particles . Electricity and magnetism are linked through electromagnetism . Electromagnetism can be in different wavelengths and frequencies but does this mean that magnetism and magnetic fields are at...
  32. K

    Max & Min Frequencies from Tuning Fork Revolution

    Homework Statement A tunning fork with frequency f = 512 Hz is held by someone who swings it vigurously in a circle in the horizontal plane. The radius of the circle is 1.0 m, and the frequency of revolution is 3.0 rev/s. (a) What are the max and the min frequencies that a second person...
  33. B

    How to get information on low frequencies of a signal using FFT?

    Hello. I've made a lab experiment of interference and with a CCD camera photographed fringe pattern which one can understand as a periodic signal. My question is: When I apply an FFT to the image is there any limit to the amplitude information I may get from lower frequencies? I read in the...
  34. S

    Amplification at high frequencies

    I am trying to read high frequency signals (as in, tens to hundreds of Megahertz) from a magnetic tape. I figure the original preamp will be unable to function anywhere near that range. So, I am trying to find a way to replace it. I have yet to get an operational amplifier to work. I keep...
  35. Z

    Do all bodies radiate at all frequencies?

    I know that all bodies with a temperature above absolute zero radiate energy away as the following. P = AeσT^4 However, I wanted to know how you could find the frequency of the power being emitted just by knowing the temperature. For example, how would I find out how much heat I need to...
  36. R

    Human Body Resonant Frequencies

    Since the old topic is locked, I had to post a new one about this (old topic here: https://www.physicsforums.com/archive/index.php/t-231156.html" ) People were talking about resonant frequencies for body parts and/or the entire body and someone was looking for a chart, not sure if this is...
  37. R

    Connection between precession and resonance frequencies?

    I'm brushing up on my knowledge behind the physics of NMR. Turns out there was a lot I had misconceptions about; I thought it was very similar to absorbance/transmittance spectroscopy. I read some material about it which threw that idea out the window. I'm now looking at a video that shows a...
  38. B

    Tension Calculation for a Vibrating Violin String

    A violinist places her finger so that the vibrating section of a 1.0g/m string has a length of 30cm, then she draws her bow across it. A listener nearby in a 20 degrees celcius room (speed of sound at this temperature in air is 343 m/s) hears a note with a wavelength of 40 cm. What is the...
  39. Z

    How Does Aliasing Affect Signal Processing in a 500Hz Sampling System?

    Homework Statement An ADC system samples at frequency of 500Hz. it is preceded by 4-pole low_pass Butterworth filter having a 3db frequency of 1KHZ. Three intefering signals are present at frequencies of 2kHz,2.6kHz and 4.4kHz a) what is the Nyquist frequency of the process? b) what will...
  40. T

    How does a crack in a free-free bar affect its natural frequency?

    if a free-free bar has a crack located somewhere along it's length, in order to find the natural frequency of the bar do you split the bar on either side of the crack and assume each bar is free/excited? What would the equation for natural frequency be in this situation?
  41. M

    Refractive index of materials at rf frequencies to make a smaller wire antenna

    I would like to ask a few questions. Does a table of refractive indices of materials at rf frequencies (say for TV) exists? Is there a way for me to estimate it for some materials? Are the refractive indices of these materials higher? Will those materials have low absorption losses at these...
  42. T

    Difference between analog and digital frequencies

    Homework Statement in the 1st lecture of DSP in the college the prof. tells us that in sinusoidal signals such as sin (wt) the (w) is the analog freq. in time domain but if it was a discrete signal (not continuous) such as sin (wTn).. wT will be the digital freq. I'm really confused and...
  43. P

    MATLAB FEM for natural frequencies and mode shapes of a beam

    Homework Statement Model the above beam with 3 elements(image provided in attachment). Calculate and list the first 6 natural frequencies Plot the mode shapes corresponding to each of the natural frequencies Homework Equations DET(M^{-1}*K + [I] \omega^2)=0 shape functions...
  44. S

    FFT coefficients and frequencies

    Homework Statement The following is the output of a 16 point computation of the discrete Fourier Transform for data taken at 10 kHz. Complete the table below by determining the frequencies associated with each of the FFT values. I attached an Excel workbook with the table. Homework...
  45. T

    Inductor and Capacitor at different frequencies

    Homework Statement When a particular inductor and capacitor are connected across the same AC voltage, the current in the inductor is higher than in the capacitor. Is this true for all frequencies? Homework Equations Current through a capacitor Ip=(Vp)(2pi)(f)(C) Current through an inductor...
  46. M

    Cut-off frequencies, Quality for a given Transfer Function

    Homework Statement Given the network transfer function H(s)=10s/(s^2+300s+10^6) Find the center frequency, lower and upper half power frequencies and the quality factor Q. Homework Equations Beta=R/L (omega naught)^2=1/(LC) BW=hi-lo=R/L H(s)=(R/L)s/(s^2+(R/L)s+1/(LC))...
  47. Q

    Are solar cells more efficient for specific frequencies of light?

    my understanding is that energy is wasted in a solar cells when light with more frequency than necessary to make an electron cross the band gap comes along and the excess energy is converted to heat. does this mean if you only shined blue light at a solar cell which had a perfect electron gap...
  48. N

    Superimposing a range of frequencies

    Homework Statement A radar antenna broadcasts electromagnetic waves with a period of 0.171 ns. What range of frequencies would need to be superimposed to create a 1.71 ns long radar pulse? Homework Equations f=1/T v=fλ The Attempt at a Solution I just couldn't understand what the...
  49. R

    Overall Sound Pressure Level between two Frequencies

    Homework Statement The band levels for a noise are 70 dB reference 20\muPa at 31.5 Hz and decrease 3 dB for each octave. Find the overall sound pressure level between 31.5 and 8000 Hz and the A-weighted sound pressure level for this frequency range. Homework Equations...
  50. P

    Resonant Frequencies and Natural Frequencies

    Hi everyone, So, resonance, are resonant frequencies and natural frequencies the same thing with a different name? If not could someone please explain the difference. Been searching for the answer for over an hour. Thanks in advance Peter
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