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. K

    Change in frequency with a small change in tension (guitar string)

    Homework Statement Homework EquationsThe Attempt at a Solution [/B]
  2. A

    Frequency of a bead on a parabolic wire

    Homework Statement Calculate the frequency of a bead with a mass of m vibrating on a parabolic track equals to y=Ax2 Homework Equations F=ma The Attempt at a Solution Looking at the bead at any point which isn't equilibrium, I have: 1. may =N-mgcosθ 2. max=mgsinθ I tried to look at a...
  3. Misha Kuznetsov

    Radio Frequency Bioluminescence

    Hello, I am just wondering whether it is theoretically possible to create radio waves through bioluminescence. I realize that most organisms produce only UV to infrared light. Are there such compounds out there that would allow an organism to make radio waves instead?
  4. D

    Classical Wavelength, frequency, and radar

    I'm doing a high school paper on the effects of frequency alterations on a radar image. Can someone recommend a book which I can use?
  5. M

    Analytical Expressions for Frequency Response

    Hi, I am struggling to understand the maths in the text shown below. (1) How does: r(t) = Acos(wt)+Bsin(wt) become; sqrt((A^2)+(B^2))cos(wt - arctan(B/A))? (2) He states that we can represent the input as a phasor and in one of three ways but doesn't say which one. (3) He then focus on the...
  6. P

    Nyquist frequency and sampling frequency

    Homework Statement ##N= \frac{2 f_s}{f_{lowest}}####\frac{f_s}{2} - \frac{f_s}{N}## Homework Equations - The Attempt at a Solution I have these equations listed on a formula sheet but I do not know what they are used for. It is from a chapter titled "Discrete Sampling and Analysis of Time...
  7. CMATT

    What frequency does the blood receive? What frequency return

    Homework Statement Ultrasound reflected from an oncoming bloodstream that is moving at 28.7 cm/s is mixed with the original frequency of 2.41 MHz to produce beats. Use the speed of sound in human tissue as 1540 m/s. Assume that the frequency of 2.41 MHz is accurate to seven significant figures...
  8. KingDaniel

    How to get frequency, w (omega), when calculating reactance

    Hi, I came across a question from our weekly set of questions that involved finding the inductive reactance and capacitive reactance, ie: XL = jwL and XC = 1 / jwC. In the solution sheet, the professor wrote that the frequency, w (omega) = 10000, however, in the question sheet, it was nowhere...
  9. Benwade

    Is photon gravity lensing affected by frequency (energy)?

    Homework Statement I am NOT a student. Please forgive my asking here, but if you do choose to answer, I would appreciate it. Obviously any or all of the statements below may be incorrect... As I understand it: The more energy a photon has (I know it's also a wave) the greater the frequency...
  10. **Mariam**

    Are frequency and energy related?

    Hello, I am studying about waves and simple harmonic motion. I have a confusion; when we studied the formula for period of pendulum and spring (T=2pi(rad(m/k))), it can be deduced that period doesn't depend on amplitude and so does frequency (T=1/f) Then we learned about how amplitude and energy...
  11. CMATT

    How Does Energy Impact Bridge Oscillation Amplitudes?

    A suspension bridge oscillates with an effective force constant of N/m. (a) How much energy is needed to make it oscillate with an amplitude of 0.106 m? (b) If soldiers march across the bridge with a cadence equal to the bridge's natural frequency and impart J of energy each second, how many...
  12. CMATT

    Wave Speed & Wavelength of Harmonic Oscillation on Slinky

    (a) A wave traveling on a Slinky® that is stretched to 4.5 m takes 2.6 s to travel the length of the Slinky and back again. What is the speed of the wave? For this one, I did v = d/t = 4.5 m / 2.6 s = 1.73 m/s Then I did v = (1.73)(2) = 3.46 m/s This is correct (b) Using the same Slinky...
  13. G

    "Intensity flicker" of Extremely low frequency (ELF) waves?

    ELF electromagnetic radiation is in the range of 3 to 30 Hz. If you had a 3Hz ELF laser pointer and you had a camera that could "see" ELF, would you be able to see the intensity of the beam "flicker" at 3Hz?
  14. A

    Why LC tank only oscillates at resonant frequency?

    I am wondering why LC tank only oscillates at resonant frequency not other frequencies? Is there a physics explanation for that?
  15. muharifiandi

    Frequency response of Torsional Vibration

    Hello engineers! I have a project to measure/ obtain natural frequency of torsional vibration. Below is the detail: 1. Object measurement: Two rotor attached to one shaft and the shaft is supported by two bearing. The shaft is connected to a motor. I give the scheme below. 2. Equipment: two...
  16. H

    Translating from Japanese: residue in capacitor?

    So, I have made an experiment of a low pass filter, and made a bode plot out of it. My experiment was done 100 percent in Japanese and this means I cannot understand completely the experiment I have done. So, there is a statement there saying the higher the frequency of the input voltage, the...
  17. S

    AC Mains frequency and microwave oven

    Does the frequency of the main affect the performance of a microwave oven? Having moved from Europe 50 Hz to the Philippines 60 Hz I can not operate my microwave oven! Is that the reason? How to remediate? Best regards.
  18. R

    Optimizing Switching Frequency for Voltage Output in a Two-System Circuit

    Homework Statement Problem and Diagram stated below System 2 Input Impedance: 1k ohms System 1 Output Impedance: 100 ohms High interpreted as Voltage greater than 2V Low Interpreted as Voltage less than 0.5V Homework Equations Capacitor Charging eqn: V=Vo(1-e^-t/RC) Capacitor Discharging...
  19. bombo

    [help] understanding Op-Amp frequency characteristics

    Hi I need help understanding the frequency characteristics of operational amplifiers. I do not understand why the output of an Op-Amp behaves much differently when the frequency of the input is increased. For example during the lab when the input to an inverting Op-Amp circuit was a sine...
  20. J

    Exploring the Doppler Effect: Frequency & Distance

    Hi all, I was just thinking about the Doppler effect today and I was wondering why distance between the source and listener does not affect the frequency experienced by the listener. Consider the Doppler formula: fL = fS*(v+vL)/(v+vS), with the positive direction taken from listener to source...
  21. E

    What Is the Resulting Frequency When Two Different Sound Frequencies Combine?

    Homework Statement When two sound sources of the same amplitude but of slightly different frequencies n1 and n2 are sounded simultaneously, the sound one hears has a frequency equal to Ans: (n1+n2)/2 Homework EquationsThe Attempt at a Solution I have virtually no clue how that's the answer...
  22. U

    What is needed to allow sound to move an object

    I am interested to know what governs whether an object in the path of a sound wave will feel force. For instance will low frequency sound have more of an effect than high frequency? What difference does the material or shape of the object have on whether it would feel any force from the...
  23. C

    System Analysis - Determining Dampening and Natural Frequency

    Homework Statement Problem and work attached. It is mostly diagrams so I have just uploaded the pictures. I think what I did to determine the transfer function was correct. I'm not quite sure how to do the last section of part (a) where I need to determine the dampening, static gain, and...
  24. A

    Frequency response of "purely ohmic" voltage divider?

    I am trying to understand why/when a purely ohmic voltage divider (impedences Z1 and Z2 are both resistors) would have a delayed response for high-speed, transient changes in an input voltage? Whether the input is high-freq AC, or simply a square wave with a sharp rise or sharp drop, I've been...
  25. Stephanus

    What information can be derived from the pulsars featured on the Voyager plate?

    Dear PF Forum, I've read the current Featured Thread in November 12nd, Lost in the Milky Way scenario. It's a good thread. But I want know what pulsar is. https://en.wikipedia.org/wiki/Pulsar A. Does pulsar(s) have unique frequency? Given the number of pulsar in our galaxy and the vast range of...
  26. T

    Engineering Find Frequency for Zero Reactance in AC Circuit

    The question is: The voltage source in the above circuit is a sinusoidal AC source with constant amplitude and constant phase shift but an adjustable frequency. Calculate the frequency ω at which the phasor current I...
  27. N

    Electron Capture by alpha particle -- Frequency of photon?

    Homework Statement Electron with KE = 50eV is captured by Alpha particle, ie. HE++. Calculate the frequency of the emitted photon. Homework Equations KE = m/2 v^2; E=hf, En = Z^2*-13.6eV/n^2 The Attempt at a Solution Energy before = Energy after 50eV = 4*-13.6eV/1 + hf f = 1200nm
  28. neduet

    Frequency convertor circuits

    A cable with concentric PE conductor must be used with frequency converter circuits what does its means.?
  29. N

    (Check solution) Frequency of light after electron capture?

    Homework Statement An alpha particle: He++ captures an electron of a given kinetic energy. To conserve energy, it emits light, hf. How would one calculate the frequency? Homework Equations E=hf En = (Z^2 *-13.6eV)/(n^2) The Attempt at a Solution Calculate En. Then KE = Photon + En. Solve for...
  30. K

    Answering the Rope Tension & Frequency Questions

    Homework Statement Identical ropes were tied to two trees, and two men, A and B, started shaking the free ends at the same instant a short while ago (Figure 1) . Which rope has the greater tension? Which man is shaking with the greater frequency? Homework Equations T=1/f λf=v The Attempt...
  31. Y

    Can a photon have any frequency or only certain specific?

    This is a very fundamental question. I apologize for its simplicity. I did searches on the web but could not find a clear explanation. Whenever I read about the principles of quantum physics, I always come across a statement along the lines of: "electromagnetic energy could be emitted only in...
  32. A

    Error in Natural Frequency (Lab)

    So I just did a lab on resonant frequency, and have to find the error of the period: $$T = 2π\sqrt{m/k}$$ m and k were measured with an error of Δm and Δk. My teacher didn't explain well how to do errors, so I just want to know if I did this right. Prorogation of Error equations: $$y=x^n ⇒...
  33. moenste

    Fundamental frequency if string halved and tension * 4

    Homework Statement The fundamental frequency of vibration of a particular string is f. What would the fundamental frequency be if the length of the string were to be halved and the tension in it were to be increased by a factor of 4? Answer: 4 f 2. The attempt at a solution We have f = f1...
  34. A

    Parasitics in Solenoids: The Relationship Between AC Frequency and Induced EMF

    If you have a one solenoid inside another (with the same number of coils of wire) the current is going through the inner one. How does the induced EMF in the outer one depend on the frequency of AC in the inner one
  35. A

    A electron cyclotron has a frequency of 2450 Hz and a magnet

    Homework Statement A electron cyclotron has a frequency of 2450 Hz and a magnetic field strength of 50T.? a) what's the speed of the electron? b) what was the voltage on the electron gun which projected the electron into the cyclotron? Homework Equations Givens: r=.4m B=50T f=2450Hz...
  36. K

    Logitech X-530 - AM radio frequency

    I have poorly made computer speakers - Logitech X-530. They sometimes pick up AM radio stations and pops up when lightning is turned off. What AM radio frequency is picked up by computer speakers? I am curious becaous some kinds of popping is picked up by computer speakers but it is not picked...
  37. onion3000

    Help with understanding modulation in AM, FM and PM radio

    I have a few questions about AM, FM and PM. 1. If FM (or PM) radio modifies the frequency of the signal, how is the signal picked up without having to change the frequency constantly? 2. If PM modulates phase, which modulates frequency, what is the difference between PM and FM? 3. Why is AM...
  38. B

    Frequency encoding gradient in MRI

    Hi, I am studying the physics of MRI (from a conceptual NOT mathematical point of view...please don't answer with heavy maths). I understand how we can obtain a signal from a specific slice along our Z-axis. I know that we then apply a graded magentic field (frequency encoded gradient) along...
  39. Blitzmeister

    Infinite Square Well Frequency of Oscillation

    Homework Statement Consider a particle in an infinite square well potential that has the initial wave-function: Ψ(x,0) = (1/√2) [Ψ_1(x) + Ψ_2(x)] where Ψ_1(x) and Ψ_2(x) are the ground and first excited state wavefunctions. We notice that <x> oscillates in time. FIND the frequency of...
  40. S

    Comparing Radio and X-Ray Galaxies: Redshift vs. Emission Mechanism

    Are all the radio galaxies in the (approximarely) same distance from us? And is the reciveing frequency from all of them in radio band? I am wondering whether the difference between a radio and x-ray galaxy is their redshift or their emission mechanism ?
  41. S

    Understanding Observing Frequency and Its Significance in Radio Astronomy

    I believe that when we say that this is radio telescope, it means that reciving frequency of it is in radio band. And also it means an observed object by that is in a particular redshift that its emission has a particular frequency that when receives us, is in radio band. Am I right? For ex. We...
  42. S

    Understanding a sound spectrum analyzer output

    Hi, I am just trying to understand the output of a sound spectrum analyzer. There are three dimensions 1) Time 2) Frequency 3) Volume (db) I am confused about few things here: 1) How should I perceive the volume dimension here? 2) Why are the db values negative here and w.r.t what reference...
  43. B

    Resonance frequency increasing with mass?

    For a spring and mass system, I've learned the resonance frequency of a system increases with decrease in mass. Not sure if this case is also related but when I attach a coin sized metal onto a piezoelectric material of a smaller size, the resonance frequency range actually goes up (from...
  44. Y

    Integration in Frequency Domain

    How to integrate $$\int_{-0.5}^{0.5} {\bigg({\frac{1}{4-2e^{-j2{\pi}f}}}\bigg)}^2 df$$
  45. B

    What Is the Correct Period and Frequency for an Electron in a Magnetic Field?

    Homework Statement Find the period and frequency of the motion of an electron of kinetic energy, E, 34 KeV as is moves in a circular orbit perpendicular to a magnetic field, B, of 0.270 T.Homework Equations For speed, v: For charge, q: For mass, m: For radius, R: For frequency, f...
  46. B

    Question about Nyquist frequency and noise

    Homework Statement A time series is sampled at 250 Hz. What is the sampling interval and Nyquist frequency of the original signal, before digitising was contaminated with noise at about 300 Hz. At what frequency would this noise appear in the spectrum of the digitised sequence ? Repeat the...
  47. goonking

    Fundamental frequency of oscillation in 2 ropes

    Homework Statement Homework EquationsThe Attempt at a Solution if the material are the same in both strings, then the density should be the same. v = sqrt (tension/μ) tension in the first string should be 30 kg x 9.8 m/s^2 = 294 N next, v = λƒ and string#2 needs to have twice the...
  48. goonking

    What is the length of a vibrating metal wire at its third harmonic frequency?

    Homework Statement A metal wire is vibrating at its third-harmonic frequency. 0.32 m from one end, the amplitude is equal to one quarter the maximum amplitude. Find the length of the wire. Homework EquationsThe Attempt at a Solution I don't quite understand the question, it says 0.32m from one...
  49. goonking

    Frequency and Length: Solving for String Length

    Homework Statement Homework EquationsThe Attempt at a Solution for the first harmonic, the wavelength is twice the length of string. so 0.296m x 2 = 0.592m is the wavelength with the wavelength and frequency known, we solve for v in v = ƒλ v = 0.592m x 440 Hz = 260 m/s then to solve for...
  50. Chrono G. Xay

    Predicting Initial Length of String Needed Before Stretch

    I have put together an equation whose purpose is: With a desired 'magnitude of static friction' ( μ_s ), 'fundamental frequency' ( f ), and 'tension' ( T ), initial conditions such as 'string breakover angle' ( Θ_0 ), 'nut-tuner distance' ( L_{h,0} ), and 'string diameter' ( d ), and...
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