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. M

    Relationship between relative frequencies of electromagnetic spectrum and sound

    I am a piano teacher with some very cool, science-minded students. Usually we stick to basic acoustics, and mechanics in terms of piano technique, but yesterday one of them took things in an interesting new direction. . . he described to me how, when he closes his eyes and listens to the music...
  2. H

    Finding Frequencies in Two Strings Stuck Together

    Homework Statement Two strings have different lengths (L1 = 3.920 m and L2 = 1.960 m) and linear densities (mL1 = 2.64E-1 kg/m and mL2 = 6.60E-2 kg/m), as the drawing below shows. |........| |........| |----------------------------------| |........| |........| (Okay, only the "-"s...
  3. M

    What happens when you pass red light through different colored glass?

    Assuming a flat pane of colored glass, using colored lights... If you pass red light through red glass, will it be blocked? How about if you pass red light through a green glass- What will the color/frequency of the light which passes through the glass be? Would you simply add the frequency...
  4. M

    How Do You Measure the Frequencies of Natural Crystals?

    If I am correct, crystal frequencies depend on the size, shape/cut, and purity of a crystal(?) How can you measure (what instrumentation) the frequency/ies of a natural crystal (other than just quartz)?
  5. N

    Negative Freq: Conclude Relation Between x(t) and x*(w)

    Hi Say I have a real quantity given by x(t) = \int_{ - \infty }^\infty {\tilde x(\omega )e^{ - i\omega t} d\omega } Now I complex conjugate it (remember it is real) x(t) = \int_{ - \infty }^\infty {\tilde x^* (\omega )e^{ + i\omega t} d\omega } How is it that I from...
  6. J

    Finding frequencies of normal modes with the systematic method

    I am having problems understanding the "systematic method" for determining the frequencies and amplitude ratios of normal modes when a system has more than one degree of freedom. I think I initially have problems setting up the differential equation that describes the motion. Here is the...
  7. G

    Guitar String and frequencies?

    Homework Statement A guitar string is 90.0 cm long and has a mass of 3.16 g. From the bridge to the support post is 60.0 cm and the string is under a tension of 520 N. What are the frequencies of the fundamental and first two overtones? L_s = 90.0 cm = .9 m L_bsp = 60.0 cm = .6 m m = 3.16 g =...
  8. A

    Frequencies & Waves Homework Solutions

    Homework Statement 1)A stretched wire vibrates in its first normal mode at a frequency of 383 Hz. What would be the fundamental frequency if the wire were one fourth as long, its diameter were quadrupled, and its tension were increased four-fold? 2)A 0.0125 kg, 1.88 m long wire is fixed at...
  9. jaketodd

    Atomic electron wave frequencies

    Hi, I am wondering what sort of frequencies electrons have in atoms at different energy levels. When I say frequency, I'm *not* talking about the frequency of the orbiting motion. I am wondering what the electron wave oscillation frequencies are at the different energy levels. A couple...
  10. N

    Can It Be Proven That Optics Field Amplitudes Satisfy Negative Frequencies?

    Hi In (quantum) optics, many authors state that the field amplitudes satisfy E\left( { - \omega } \right) = E^* \left( \omega \right) But how is it that one can prove that this is correct? I have never seen any book do this,
  11. D

    Vibrational Stretching Frequencies of some Diatomics

    For an assignment (not really homework, but not really exciting either), I'm trying to calculate the total entropy for the reaction: Na2 + X2 \rightarrow 2 NaX Where X = F, Cl, and Br . ( I told you this isn't exciting). Also, in this theoretical reaction, everything involved is an...
  12. A

    Possible frequencies of an electron

    Hi Could someone kindly clarify the following? Homework Statement In its ground state the atom absorbs 2.3 × 10–19J of energy from a collision with an electron. (i) Calculate all the possible frequencies of radiation that the atom may subsequently emit. Homework Equations E=hf...
  13. F

    Undamped natural frequencies

    Hello everybody, I have a question about the undamped natural frequencies for a three degree of freedom system. The equation of motion for the undamped system is : M\ddot{x}+K\dot{x}=0 The undamped natural frequencies I found is a complex number ...
  14. S

    Finding frequencies given AC voltage samples

    Homework Statement Hey. I am new here. Recently i got a C assignment (computing) in which i was given around 20 files..each with thousands of AC voltage test samples sampled at 1 ms..so technically 100 samples= 1 second. I was told that there 3 different kinds of frequencies in the files and...
  15. B

    Resonance/ Natural Resonance Frequencies?

    I am doing a small physics research project introducing sound, resonance, and natural resonance frequencies, but I have questions. I know that resonance is the tendency of a system to oscillate with larger amplitudes at some frequencies rather than others. Does this just mean that the...
  16. L

    Why do certain frequencies of radiation react with some things an not others,

    For example, why is it that sand stays hot even after the sun goes out, stopping the source that excites its electrons, shouldn't that make it immediately cold, or is the radiation released in a shorter amount of time, and if so how?
  17. C

    Waves question RE combination of frequencies and semitones

    Homework Statement musical notes are defined by the frequency of oscillation. however notes are usually not qualifies in terms of absolute frequency, but the ratio (called interval) of their frequency to that of a reference notes called root. Pythagorus discovered that intervals that please...
  18. S

    Oscillation Frequency of superposition of two oscillations of different frequencies

    Homework Statement Find the frequency of combined motion of the following (a) x = sin (12pi.t) + cos(13pi.t + pi/4) (b) x = sin(3t) - cos(pi.t) Homework Equations The book I'm using states that if the periods are commensurable ie if there exist 2 integers n1 and n2 such that n1T1 =...
  19. B

    De Broglie's wave frequencies for particles

    I was reading today about de Broglie and I don't think I really get what is meant by particles having a wave frequency. What is being measured as a wave, the oscillation of the electrons? Also, the book said something about the electrons sending out waves that move faster and even catch up...
  20. pellman

    Signicance of positive and negative frequencies?

    Reading some QFT in which we are faced with inhomogeneous equation (\partial^\mu \partial_\mu + m^2)\phi(x)=J(x) The solution is given as \phi(x)=\phi^{(+)}_{in}(x)+\phi^{(-)}_{out}(x)+i\int{d^4 x\Delta(x-x')J(x') where \Delta is the appropriate Green's function. "in" means the...
  21. B

    Comparing Bandwidth: PCI Bus vs. FireWire (IEEE 1394)

    The PCI bus found in many computers transmits 64 bits per clock cycle at 33MHz. How does the bandwidth of the PCI bus compare to the serial FireWire (IEEE 1394) serial bus specification, which is 400 Mbits per second? a. The FireWire serial bus is better. b. The PCI bus is better. c. They...
  22. F

    Identifying resonant frequencies in various objects

    Hi I was wondering if someone would be kind enough to help me with a project I have at the moment. Here is the scenario; I am playing various tones through a speaker system at a fridge and I need to be able to detect which of the tones make the fridge resonate. I have been using a...
  23. M

    Exploring the Moon: Discovering Lunar Frequencies and Radiations

    Hy. I want to find a lot of info about the moon. I've read about gravity. I want to know about the frequencies, radiations and whatever there is, and how them interact with earth. Where should i search? Thanks!
  24. M

    Why do waves(in general) travel in different frequencies?

    Why does a wave go up and down? What forces cause waves to go up and down? In order for a particle to be a specific frequency would depend on what?
  25. C

    Frequencies on a violin string

    A violin string has a length of 0.350 m and is tuned to concert G, with fG = 392 Hz. Where must the violinist place her finger to play concert A, with fA = 420 Hz? If this position is to remain correct to half the width of a finger (that is, to within 0.600 cm), what is the maximum...
  26. A

    Do Fleming valves fail at high frequencies?

    So I've been reading up on optical rectennas, and the sources I read say that the reason such devices are not yet efficient enough to be practical isn't the antenna, it's the rectifier, since solid-state Schottky diodes of the types normally used don't work in the THz range of AC frequencies...
  27. W

    Solving Sampling Frequencies: Discrete Time Signal & Nyquist Frequency

    Homework Statement x(t) = 3*sin(1000*pi*t) Suppose that the signal is sampled at a rate of fs = 2000Hz. What is the discrete time signal obtained after sampling (i.e., the signal expressed as a function of sample number n, x[n]) What discrete time frequency, f-hat will the signal x[n]...
  28. M

    Do gravitational waves have different frequencies?

    I'm wondering if gravitational waves can have a wide range of frequencies and wavelengths much like EM waves, or if they are more uniform and only vary in amplitude. Also, should gravitational waves experience a Doppler shift?
  29. T

    Musical Frequencies Overtones, ratios

    Homework Statement Two strings on a musical instrument are tuned to play at 262 Hz (C) and 294 Hz (D). Questions: 1. If the two strings have the same length and are under the same tension, what must be the ratio of their masses (MC/MD)? 2. If the strings, instead, have the same mass...
  30. B

    Vibrational frequencies of molecules

    Homework Statement The mass of the deuterium molecule D2 is twice that of the hydrogen molecule H2. If the vibrational frequency of H2 is 1.22 × 1014 Hz, what is the vibrational frequency of D2, assuming that the “spring constant” of attracting forces is the same for the two species? Answer...
  31. J

    2 D.O.F System - Natural Frequencies

    Homework Statement The question is a 2 D.O.F system, m1 = 600kg, m2 = 50kg, k1 = k3 = 0.5MN/m, k2 = 0.2 MN/m. Calculate the natural frequencies. Homework Equations 1167-w^2 -333.3 X1 0 = -4000 14000-w^2 X2...
  32. T

    Output specific frequencies with digital electronics

    I'm trying to figure out how to build a breadboard instrument using either push buttons or logic switches as they keys that will play each note. The issue that i am having is that I don't think finding all of the perfect resistor and capacitor combinations for each note is a good idea. So, i...
  33. K

    Normal frequencies of vibration of a molecule

    Hello, I am new in computational chemistry. I was calculating by "Moller Plesset Second Order perturbation theory -MP2-" (using GAMESS) molecular parameters of Cs3Cl2-. Among them i found two complex frequencies of vibration. My question is now, what is the physical meaning of those complex...
  34. S

    Design digital logic clocks with given frequencies

    Homework Statement Assume you have a symmetrical clock at 100MHz. Design a logic circuit with four outputs of clocks at 100MHz, 50MHz, 25MHz, and 12.5MHz. The logic circuit should have 2 inputs to select output clock rate. Homework Equations N/A The Attempt at a Solution For...
  35. I

    Theoretical and actual limits to electromagnetic frequencies?

    i'd like to know two things a) is there a theoretical upper and/or lower bound to electromagnetic frequencies in the universe? I'm thinking for an upper limit, 1/planck time? for a lower limit, i have no idea-- does Heisenberg uncertainty calculate into that? i suppose it would when you...
  36. B

    Bus Frequencies and Ohms Law

    What does increasing the frequency of a computers main bus [the bus that connects the CPU to the chipset] imply about the voltage ["information"] traveling on a bus? (what IS the frequency of a bus effectively measuring, data units per second?) The way i see it (please correct me if I'm...
  37. A

    A simple example where oscillations with two or more frequencies are combined?

    I just need a simple example, preferably one to do with voltage. thanks for any help :)
  38. A

    Vibrations problem - Deriving the natural frequencies

    Homework Statement A thin beam of length L (flexural Stufness EI, cross-sectional area A, density p) is connected to a linear spring of stiffness K_s at each end. Derive the governing equation for the natural frequencies of transverse vibrations from the beam equation and boundary conditions...
  39. S

    Angular velocity, the Doppler effect, and frequencies.

    Homework Statement A speaker is attached to a wire 1.5 m long and is spun in a circle at 2 rev/s. The speaker is connected to an electric piano on which a child is playing a note at 261 Hz. Speed of sound in air is 343 m/s. What range of frequencies will the stationary observer hear? I...
  40. R

    Induced seismicity and low frequencies

    Maybe a dumb question, and I've been wondering this a long time, but the Haiti thing reminded me... Is it possible for electronically produced frequencies to cause seismic activity? I know that injection wells/fracturing/oil & gas wells/dams can cause induced seismicity, but is there anyway at...
  41. B

    How Do Natural Frequencies Arise in a Clamped Metal Rod?

    Homework Statement A thin, flexible metal rod has a length of 0.606 meters. One end of the rod is clamped to a table, and the other end can vibrate freely. What are the first three natural frequencies of the rod if the wave speed in the rod is 27.4 meters per second? Hint: Draw pictures of...
  42. B

    Question on Natural Frequencies

    Homework Statement The speed of transverse waves along a stretched spring is 9.05 meters per second. The spring is 4.70 meters long and is held in place at both ends. What are the first three natural frequencies of the spring? Hint: Draw pictures of what the spring will look like when it is...
  43. T

    Natural frequencies of rectangular membranes

    Hello physicsforums members, I am an engineering student at Purdue University and am currently conducting research with regards to ribbon transducers. A ribbon transducer consists of a rectangular element of metal foil suspended within a magnetic gap (ie free at the sides) and...
  44. S

    What Happens to the Fundamental Frequency When Modifying a Drinking Straw?

    Homework Statement If you blow air over the top of a fairly large drinking straw you can hear a fundamental frequency due to a standing wave being set up in the straw. Match the following actions with their consequent results: 1. While blowing, you cover the bottom of the straw with your...
  45. C

    Finding the possible frequencies of a tuning fork

    Homework Statement A 0.0120 kg, 2.05 m long wire is fixed at both ends and vibrates in its simplest mode under a tension of 202 N. When a tuning fork is placed near the wire, a beat frequency of 5.10 Hz is heard. What are the possible frequencies of the tuning fork? (enter the smaller...
  46. C

    Summation of continuous band of frequencies

    Just got a "thought experiment" question from a colleague. The question, as phrased was: If an audio signal was composed by adding all of the frequencies in the audible range, what would it sound like? I thought it was interesting, so I attempted to solve it by integral. My calculus skills...
  47. Z

    Sound waves - Combined Frequencies

    Homework Statement Two tuning forks 384Hz and 256Hz. The question asks - would the sound of the combined frequencies be more similar to the 256 or 384Hz tuning fork. Estimate the frequency of the complex wave (noting that the pattern is repeated over three times). We are given two...
  48. S

    Pion decay and photon frequencies

    Homework Statement we are given a neutral pion moving at 0.98c straight in the x-direction. The pions rest mass is 135MeV/c^2. two photons are emitted in opposite direction parallel to the pion's motion. I need to find the two frequencies of each photon. Homework Equations m=0...
  49. M

    Musical Acoustics, Combining frequencies of two instruments

    Homework Statement A certain dog whistle operates at 21.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the...
  50. J

    What does Q have to do with frequencies?

    Could someone explain why Quality factor, which as I understand it, is 2pi *(maximum energy stored/energy dissipated per cycle) is related to the resonant frequency/bandwidth? I don't understand the connection between the two concepts. Thanks, John
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