What is Wavelength: Definition and 1000 Discussions

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, troughs, or zero crossings, and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. The inverse of the wavelength is called the spatial frequency. Wavelength is commonly designated by the Greek letter lambda (λ).
The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency of the wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths.Wavelength depends on the medium (for example, vacuum, air, or water) that a wave travels through. Examples of waves are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary. Water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary.
The range of wavelengths or frequencies for wave phenomena is called a spectrum. The name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum.

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  1. J

    Propagation of uncertainty from wavenumber to wavelength

    Hi, This is just a quick question. If wavenumber is a variable with some standard deviation Δk, how do I propagate this spread when converting from wavenumber to wavelength? Is it just 2π/Δk or is it more complex than that? Thanks
  2. B

    The Relationship Between Wavelength and Amplitude of Photons and Electrons

    Is there a relation between the wavelength and the amplitude of a photon (or particle), or all frequencies have the same amplitude? If the latter, why the wavelength affects the way a radiation passes through matter or slits? Thanks.
  3. I

    Classical wavelength versus wavefunction

    Hi, I was reading about interference patterns. I was wondering if the classical interpretation of the wavelength of the photon according to maxwell's is the actual wavelength of the photon in the wavefunction? Are the two related? Thanks!
  4. O

    How Do You Calculate the Wavelength of Sound Waves Emitted by a Violin String?

    I am doing this problem: (a) Find the speed of waves on a violin string of mass 800 mg and length 22.0 cm if the fundamental frequency is 920 Hz. (b) What is the tension in the string? For the fundamental, what is the wavelength of (c) the waves on the string and (d) the sound waves emitted...
  5. B

    Diffraction pattern's dependency on wavelength

    Hello. 2 questions: 1. If a diffraction grating is smaller, approaching infinitely smaller, than the wavelength of incident light, what happens to the diffraction pattern? Does the wave still diffract at all? 2. Wavelength is the distance between two crests of periodic motion. Imagine...
  6. R

    Radiant (all wavelength) flux emitted by a light source

    hello If I were to hang a traditional 100W clear glass light bulb from the ceiling, would it radiate 80W (radiant flux), the other 20W lost by air convection/conduction up the wires, or would it radiate closer to 60% or 40% of consumed energy? I can find plenty of figures for the...
  7. V

    Smallest Difference in Wavelength the Human Eye Can Notice

    Hello - I'm having a difficult time finding this answer anywhere else on Physics Forums. I'm curious if anyone knows, or can figure out, the smallest difference in wavelength that the human eye can notice. For example: Can the human eye detect if a light changes from 568nm to 570nm?
  8. X

    Standing Waves Tension and wavelength

    Homework Statement Please see the picture. Homework Equations How do they get this derivation? The Attempt at a Solution I know that lambda = 2L/n and f = nV/2L so I can somewhat rearrange it myself, but I do not know where the square root is coming from.
  9. H

    How to calculate pulsar's wavelength by it's diameter and mass?

    Hello. I came to this forum to seek help for this question, since I cannot find it anywhere on the internet, nor even books. I have to calculate a maximum of a radiated wavelength of a neutron star. Sorry I don't know how else could I translate it from to English. All I was given is that it's...
  10. A

    Thin Film Interference and wavelength

    Homework Statement Light of wavelength 550 nm in air is normally incident on a glass plate (n=1.5) whose thickness is 1.1 X 10^-5 m. (a) What is the thickness of the glass expressed in terms of the wavelength of light in glass?(b) How many reflected waves will experience the 180 degree phase...
  11. S

    Question regarding the de Broglie wavelength of a particle.

    Homework Statement A particle with charge e and mass m_0 is accelerated by a potential V to a relativistic speed. Show that the de Broglie wavelength is: λ = h / √(2 m_0 eV ) √(1+( eV / 2 m_0 c^2 )) Homework Equations E = qV λ = h/p E = √(p^2 * c^2 + m^2 * c^4 ) p = (m_0 * v) / (1 -...
  12. C

    Relativistic Wavelength of Electron in Transmission Electron Microscop

    [I could not fit the last "e" into the title] Hi! I am writing a report on TEM, and was asked to consider the effect of accelerating voltage on the resolution. Since resolution in the light microscope is limited by the wavelength of visible light, we obtain much higher resolutions in a TEM...
  13. PsychonautQQ

    Power radiated through a hole in small wavelength distribution

    Homework Statement A cavity at Temperature 6000k has an energy distribution corresponding to a blackbody. We make a small hole in it 1mm in diameter. Calculate the power radiated through the hole of wavelength interval between 550nm and 551nm. HINT: when dλ is small (such in this case)...
  14. D

    No change in wavelength of a monochromatic light

    I searched for the images of refraction on google images and i saw an image where a laser light was incident on a regular glass slab. Bending of light was clearly seen in the picture. According to Snell's law the refractive index of any particular medium is the ratio of angle of incidence to...
  15. N

    What Does Higher Permittivity Substrates Mean for Unit-to-Wavelength Ratio?

    hi friends, can anybody clear my concept about the following sentence. " if we use substrates with higher permittivity, like quartz or GaAs that has been used in previous successful experiments, the unit cell will have smaller unit-to-wavelength ratio".
  16. 4

    What is the Minimum Depth of Water for Standing Sound Waves in a Drinking Glass?

    Homework Statement We place a speaker near the top of a drinking glass. The speaker emits sound waves with a frequency of 3.75 kHz. The glass is 14.1 cm deep. As I pour water into the glass, I find that at certain levels the sound is enhanced due to the excitation of standing sound waves in...
  17. T

    Determine radius of wavelength

    Homework Statement In the figure, sound with a 38.0 cm wavelength travels rightward from a source and through a tube that consists of a straight portion and a semicircle. Part of the sound wave travels through the semicircle and then rejoins the wave that goes directly through the straight...
  18. U

    Fractional change in wavelength

    Homework Statement When a photon is emitted from an atom the atom recoils. The kinetic energy of recoil and the energy of photon come from the difference in energies between the states involved in the transition. Suppose a hydrogen atom changes its state from n=3 to n=2. Calculate the...
  19. R

    Doppler effect vs expansion effect on wavelength

    Could you please clarify for me how much each of these contribute to the red shifting of light from distant objects? It seems to me that red shifting of light from near by objects i.e. within our galaxy would be affected more by the Doppler effect whereas for intergalactic objects the red...
  20. V

    Determining index of refraction and wavelength of a visible spectrum?

    Homework Statement You decide to become a forensic pathologist because you enjoy working with dead people-they don't talk back-more than with the living. In one murder investigation, you find an unknown liquid in the victim's stomach. To identify this liquid, you pour a known amount of it onto...
  21. V

    Period, frequency, wavelength, and velocity of a light wave

    Homework Statement A light wave has a frequency of 6 x 1014 Hz. A) What is its period? B) What is its wavelength in a vacuum? C) When the light wave enters water, its velocity decreases to 0.75 times its velocity in vacuum. What happens to the frequency and wavelength? Homework Equations...
  22. R

    Units of the Thermal de Broglie wavelength?

    1. Units of the Thermal de Broglie wavelength? 2. λ = h / (2*pi*mkT)^(.5) 3. through dimensional analysis i get S (J / kg)^.5 can you even have .5 of a unit?
  23. C

    How can diffraction occur with gap smaller than the wavelength?

    I was wondering if diffraction of a wave can occur when the gap through which the wave passes is shorter than the wavelength itself. Then I came across this website http://www.talktalk.co.uk/reference/encyclopaedia/hutchinson/m0015966.html Which says that "In order for this effect to be...
  24. J

    The Wavelength of a Photon: A Mathematical Representation or a Physical Reality?

    Does the wavelength of a photon actually mean wavelength? Because as I understand it, a force field, be it gravity, EM, ect..., has influence at any distance. Theoretically, the field never has an end, reaching out across the whole diameter of the universe, even though the effects would be...
  25. R

    Wavelength of 60MHz Wave: Explained

    What is the wavelength of a wave that has a frequency of 60MHz?
  26. M

    Wavelength of ejected electrons

    Homework Statement The threshold frequency of a metal is 3.184 x 10^14 Hz. If a photon of wavelength 368 nm strikes the surface of the metal, what is the wavelength of the ejected electron? Homework Equations f (frequency) = c/(wavelength) Eincident = Ethreshold + KE E=fv(wavelength)...
  27. P

    Two wave superposition with different wavelength , amplitude and frequ

    Homework Statement Hi Two wave superposition with different wavelength , amplitude and frequency u1(x,t)=A1cos(k1x+w1t) u2(x,t)=A2cos(k2x+w2t) a)Show that an amplitude modulation is obtained Homework Equations No relevant equations The Attempt at a Solution...
  28. STEMucator

    Double Slits, Calculating Wavelength

    Homework Statement The following data was obtained upon using a double-slit experiment. Use this data to determine the wavelength of light being used to create the interference pattern. Do this in three different ways. - The angle to the eight maximum is 1.12° - The distance from the slits to...
  29. J

    Is there a wavelength shift in the way digital cameras represent color

    After going on a ghost tour over Halloween, several people were able to take photos of ghosts seen through an old hotel window, a few stories above our position. This got me to wonder if this was a trick that relied on the way that the digital cameras may be able to detect non-visible...
  30. Nugso

    Frequency, Velocity and Wavelength of Light

    Hello all. When light goes through one medium to another, its velocity and wavelength change but frequency remains the same. If the wavelength of light decreases, the length between two crests decreases, doesn't that mean there will be more wave hence frequency will have to increase? I tried to...
  31. T

    Wavelength on power transmission lines

    At the power-line frequency (50Hz), the wavelength of electromagnetic waves in free space is 6,000 km. Similarly, the phase velocity of voltage/current waves is about 4,000 km at this frequency. The question is, why do we bother about the wavelength at all at the power-line frequency, when the...
  32. D

    Why is a 1/4 wavelength antenna limited to 1/4 wavelength length?

    Why does a 1/4 wavelength antenna have to be 1/4 wavelength? What property of the wave is responsible for this restriction? I've been trying to understand how a 1/4 wavelength antenna works and the best explanation, relatively speaking, was on the following website...
  33. N

    Wavelength of sound and windspeed

    Both source and observer are at rest. If the wind blows from source to observer will the wind affect the wavelength of sound??
  34. K

    What is the relationship between wavelength and excited shells in atoms?

    is the wavelength equal to the distance between the excited state shell and the rest state shell?
  35. C

    Double slit experiment: effect of changing wavelength

    Homework Statement The question is regarding Young's double slit experiment. "Describe the effect, if any, on the separation and on the maximum brightness of the fringes when the following changes are made. ... ... 2) The wavelength λ is increased to 1.5λ, keeping a and D constant...
  36. A

    Help understanding about wavelength

    Hi, I want to ask one question about wavelength. Here is a picture defining wavelength. To get a sinusoidal wave in space, we have to use a sinusoidal voltage source at transmitter, right? I mean if there is a sinusoidal voltage source at the transmitter to create a sinusoidal wave in space.
  37. B

    Can you correctly measure wave properties but get wrong wavelength?

    Homework Statement You and a friend each have one rope. You tie the two ropes together and stand as far apart as possible, each holding one end of the new longer rope and pulling to put it under tension. You then begin moving your arm in such a way as to produce a harmonic wave with a...
  38. skate_nerd

    Wavelength for highest radiation per unit wavelength

    Homework Statement At what wavelength does a cavity at 6000 degrees Kelvin radiate most per unit wavelength? Homework Equations $$\rho_T(\lambda)d\lambda=\frac{8\pi{hc}}{\lambda^5}\frac{d\lambda}{e^{{hc}/{\lambda{kT}}}-1}$$ The Attempt at a Solution I'm pretty new to this whole...
  39. M

    Find frequency given wavelength and distance travelled

    Homework Statement Project Seafarer was an ambitious program to construct an enormous antenna, buried underground on a site about 4000 square miles in area. Its purpose was to transmit signals to sub-marines while they were deeply submerged. If the effective wavelength was 1.0x10^4 Earth...
  40. AdrianHudson

    What is the wavelength of an electron moving at 1 m/s?

    Homework Statement What is the corresponding wavelength, in meters, of an electron moving at 1 m/s? Velocity: 1 m/s Planks Constant = 6.626 069 57 x 10^-34 Mass of electron = 9.109 382 91 x 10^-31 Momentum = unknown Homework Equations We need to find momentum to use De Broglie's equation...
  41. K

    [Waves] Wavelength and surfaces penetration

    Hi everybody! Just 2 important notes: I don't study physics and so I'm not sure if this question belongs here (but I don't know where should I put it..); second I'm not english native, so ask me if I did not explain somthing enough. My electronic professor told once in my class, that you...
  42. M

    What Happens When Two Wavelengths Are Modulated at the Same Frequency?

    hi what would happen if i modulated two wavelengths with the same intensity modulation frequency? for example if i had 2.0um light and 1.5um light and modulated them both with the same frequency, would sidebands develop around each wavelength? or would they interfer in a more complicated...
  43. I

    Should i be worried? (UV lamp wavelength)

    (not exactly sure where I'm supposed to post this) i was looking at my UV lamp that i got from walmart. i was looking for a wavelength on there but i only saw "color temperature" i immediately thought Wien's law; so then i calculated the peak wavelength and got 96nm which is on the far side...
  44. I

    What Is the Wavelength of White Light?

    I know the visible spectrum,(400nm(violet)-750nm(red)) but I can't seem to find the wavelength of white light, can anyone help me out with this?
  45. D

    Is an emission spectrum really independent of excitation wavelength?

    I've often read that the emission spectrum of a fluorescent molecule is independent of the wavelength used for the excitation. But what happens in the case of a small Stoke's shift where the excitation and emission wavelengths overlap? If I use a narrow band excitation with a wavelength in...
  46. G

    Heisenberg uncertainty principle and wavelength of light

    I read somewhere that Heisenberg described his uncertainty principle by saying that you can't measure position more accurately than the wavelength of light (which makes sense), so Δx > λ. This is what I don't get. He then says that p=h/λ, so Δp > h/λ2 Δλ. He the multiplies and sets Δλ ≈ λ to...
  47. N

    EMR Wavelength: Frequency & Electric Fields

    How are the wavelength and frequency of light measured experimentally, are the equal to frequency of their consistent electric and magnetic field motion's frequency...
  48. A

    Possible webpage title: What is the Definition of Wavelength in Physics?

    Hello Dear people,i wanted to know wat actually is wavelength?? I have heard all the definations most of them says its difference bw two crest or trough..that is ok.most of the people understand wavelength as path of particles while travelling..is it true?? wat is meant by wavelength of...
  49. C

    How to get wavelength of the wave function?

    A particle in the infi nite square well potential is found at the 3-rd excited state. What is the wavelength of the wave function of the particle? this is a mcq from my faculty who denoted the correct answer to be 2/3 a ...how to get that ?
  50. H

    Controling the wavelength of an LED through voltage?

    I was reading some spec sheets for some leds, and it says that, for example, at 1.4V the light is at 650nm and that at 1.7V the light is at 670nm. This is a feature that could be potentially quite useful to me, so I was wondering: is this a common feature of leds? Is it dangerous to change...
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