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. K

    Wavelength of New Laser with Diffraction Grating Measurement

    Homework Statement To confirm the wavelength of a new laser, a scientist prepares a diffraction grating with a distance of 5.00 x 10^-6 m between slits and places it in front of the laser which is 1.50 m in front of a screen. The scientist measures the distance from the central maxima to the...
  2. Q

    Photon Flux per Unit Wavelength

    Hi How do you get a photon flux per unit wavelength curve for solar radiation? My understanding of "per unit wavelength" is that the wavelengths within a very short range are fired at a detector. The range is then gradually changed to cover higher wavelengths. The values of flux measured by...
  3. F

    Wavelength Speed: 10nm vs 1mm - Does UV Travel Faster?

    Would light at 10nm be traveling at a slower speed due to having to go a shorter distance than light at 1mm? The IR light is traveling a straighter line to its destination than the UV so for both of them to arrive at the same time the UV must be going faster in order to make up time and be at...
  4. E

    Wavelength of scattered photon and angle of scattering in the Compton scattering

    Homework Statement In the Compton scattering, a photon of wavelength λ collides with an electron at rest, and a new photon of wavelength λ' emerges at an angle θ. Find λ' y θ. Energy of incident photon Ei = 1 MeV Energy of scattered electron Ee = 0.32 MeV Homework Equations E =...
  5. E

    Threshold frequency and wavelength of electrons in the photoelectric effect

    Homework Statement Electrons are emitted from a metal as a consequence of their absorption of energy from a light beam. Find the threshold frequency of the metal and the wavelength of emitted electrons. Wavelength of incident light λ = 500 nm Work function of the metal \phi = 2.1 eV Homework...
  6. A

    Flux Density (Jy) to Luminosity when wavelength is involved

    Hi, I think my problem may be a little trivial however I have been stuck on it for quite some time. I have plots of flux density (Jy) versus wavelength in order to look at a particular forbidden line. I want to find the luminosity of the line, however as I am dealing with Jy [W/(m^2 Hz)] I do...
  7. S

    De broglie wavelength and lorentz contraction

    Am I correct in thinking that the quantum mechanical de broglie wavelength explains relativity's contraction of matter? because lambda = h/p, as the velocity of say a proton increases, the momentum also increases, and the wavelength should get smaller because lim p-->infinity of h/p = 0. At very...
  8. H

    Visible light wavelength discrepancy on the EM spectrum?

    Hello all, I'm not all too familiar with the electromagnetic spectrum, nor generally with physics but there is something that keeps me up. I learned, and also read now everywhere that visible light (to humans) lies in the wavelength range of about 400-700 nm. No I have a science book here...
  9. C

    Calculating Light Source Power from Photon Concentration & Wavelength

    Hello all of you very bright physicists, The local physics dept. is not answering us thus far and long story short we need a rough estimate of the power of a light source based on wavelength and a measured concentration of photons. We need a method of converting the photon concentration...
  10. B

    Help understanding solar imaging wavelength and coronal temp

    The TRACE website has a solar image that is described as, quoting from the text associated with the image, "This is a false-color, 3-layer composite from the TRACE observatory showing the solar corona: the blue, green, and red channels show the 171A, 195A, and 284A, respectively. These TRACE...
  11. T

    Is there any relation between wavelength and brightness?

    What makes, for example, blue color appear darker or lighter? Is it just amount of photons (intensity) or is there any relation between brightness and wavelength? Or is there something else that comes into equation as well?
  12. T

    De broglie wavelength of fast moving particle-help please

    De broglie wavelength of fast moving particle--help please! Homework Statement A particle moving with kinetic energy equal to its rest energy has a de Broglie wavelength of 1.7898 *10^-16 m. If the kinetic energy doubles, what is the new de Broglie wavelength? Homework Equations...
  13. K

    De Broglie wavelength from scattering of neutrons on crystal

    Homework Statement A certain crystal has a set of planes 0.33 nm apart. A beam of neutrons strikes the crystal at normal incidence and the first maximum of the diffraction pattern occurs at ∅= 38°. What is the de Broglie wavelength of the neutrons? Homework Equations nλ = Dsin∅ where D...
  14. S

    What are phasors and how do they relate to determining the wavelength of a wave?

    Homework Statement My physics text states: "We can represent a string wave (or any other type of wave) vectorially with a phasor." Now, for phasors the amplitude and angular frequency are given. If this is the case though, how is k, the angular wave number (and hence the wavelength)...
  15. P

    Determining Maximum Wavelength of Incident Radiation

    Homework Statement When a certain metallic surface is illuminated with electromagnetic radiation of wavelength λ max kinetic energy of photoelectrons is 40.5 eV. On same surface infrared radiation of 3λ, the ma kinetic energy is 5% less than that of incident radiation. Determine the maximum...
  16. M

    How Does de Broglie Wavelength Affect Particle Behavior in Helium Gas?

    The atoms in a gas can be treated as classical particles if their de Broglie wavelength is much smaller than the average separation between the particles. Compare the average de Broglie wavelength and the average separation between the atoms in a container of monatomic helium gas at 1.00 atm...
  17. X

    Wavelength of Particle Passing Through Potential Barriers

    Homework Statement Compare the wavelengths of a particle when it passes a barrier of height (a) +V0 and (b) -V0 where E > |V0|. Calculate the momentum and kinetic energy for both cases. Homework Equations (see below) The Attempt at a Solution I know the wavelength changes in the...
  18. A

    What is the wavelength of the light？

    Calculate the wavelength of the light emitted when an electron in a one-dimensional box of length 5.2nm makes a transition from the n = 7 state to the n = 6 state. Express your answer with the appropriate units. I calculated in this way: E = n^2*h^2/8*m*a^2 E=...
  19. V

    Confused about definition of wavelength

    Wavelength of a sinusoidal wave is defined as the spatial period of the wave, which can be measured between any two points on the wave where the shape repeats. But if my wave is defined as a function of time (like those of a simple harmonic oscillator), how can you say the distance along the...
  20. S

    Electron Wavelength in Infinite Potential Well

    I'm a little confused about the electron wavelength in an infinite potential well. It is my understanding that the maximum wavelength that the electron can achieve is 2 times the length of the potential well. As the eigenvalue increases, does the wavelength change? I believe that the...
  21. C

    Increase in Wavelength of an LED Immersed in Liquid Nitrogen

    Hi, I've been working on an experiment where I dip LEDs into liquid nitrogen and note the color change. All online sources I've seen predict that the wavelength of the light emitted by the LED will decrease upon immersion. What I've been observing, however, is a sudden decrease in...
  22. P

    Wave Nature of Light - Calculating Wavelength (Double Slit Exp)

    Homework Statement Monochromatic light falls on two very narrow slits 0.046 mm apart. Successive fringes on a screen 5.30 m away are 7.0 cm apart near the center of the pattern. Determine the wavelength of the light to two significant figures. Homework Equations x2 ≈ Lθ2 = L (2λ) / d...
  23. A

    Momentum of a proton in de Broglie wavelength

    Homework Statement In quantum mechanics the de Broglie wavelength of an object depends on its momentum according to λ=h/p where h is Planck's constant. Protons of charge e and mass m are accelerated from rest through a potential V. What is their de Broglie wavelength? A) 2h/\sqrt{}meV...
  24. G

    Electron wavelength in superconductors

    What is a rough figure for the wavelength of the moving electrons in a superconductor? Or is there no easy answer for that?
  25. C

    Plancks law: Relationship between peak wavelength and peak frequency

    Homework Statement What is the relationship between vmax and λmax and why isn't it just vmaxλmax = c Homework Equations vλ = c vmax = 5.88 x 1010T s-1 K-1 λmax = 0.290T-1 cm K The Attempt at a Solution I worked out that Bλ = -dv/dλ Bv where -dv/dλ = c/λ2 So I...
  26. C

    Why is the Flexural Wavelength Dependent on Density?

    I'm familiar with the derivation of flexural wavelength (λ=(4*D/gΔρ)^.25), but have no intuition for why λ's dependent on Δρ. My intuition tells me if you put a mass on a plate and it bends a little, then you increase the mass, the amplitude of the bend will change, but not the wavelength...
  27. C

    Gas Absorbs Light: 500nm Wavelength in Lab

    Homework Statement a gas that absorbs light of wavelength 200 nm in the laboratory. Suppose there is a cold cloud of the same gas between you and a hot source of continuum (blackbody) radiation, and the cloud is moving away from Earth. You will see a spectrum with Homework Equations...
  28. D

    Electrons motion at de broglies wavelength

    Homework Statement When an electron moves with a certain de Broglies wavelength, does any aspect of the electrons motion vary with the wavelength. Homework Equations λ=h/p p=mv The Attempt at a Solution Ok so I realize that under certain conditions electrons wavelike properties can be...
  29. Z

    Archived How Do You Calculate the Wavelength of an Electron with 1keV Kinetic Energy?

    Homework Statement Homework Equations de Broglie wavelength λ = h/p E^2 = p^2 c^2 + (m0)^2 c^4 L-compton = (h-bar) / mc The Attempt at a Solution I'm trying to work out the wavelength of an electron with a kinetic energy of 1keV So I intend on using de Broglie...
  30. K

    Solving Phase Change & Spatial Separation with Wavelength & Velocity

    Homework Statement A wave of wavelength 75 cm has velocity 375 m/s. a. What is the spatial separation between two points that are 30° out of phase at a particular time? b. What is the phase change at a particular position for a time change of 0.5 ms? Homework Equations u = λ / T...
  31. A

    Light wavelength passing through a grating sketch help

    Homework Statement light with a wavelength of 520 nm abd 630 nm passes through a diffraction grating that contains 6000 lines/cm. a) sketch a diagram of the image produced from m=0 to m=2, label the order of each fringe b) calculate the angles for the first and second order maxima that...
  32. Z

    De Broglie wavelength and Fermi wavelength

    As we know that the properties of nanoscale material are quite diffrent from the bulk's. But what's the threshold of the size, or what the upper limmit where significant difference can be observed? The De Broglie wavelength or the Fermi wavelength of the electron in material? How to understand that?
  33. K

    Find sound wavelength from a vibrating string

    Homework Statement Sound Wavelength From String During a concert a pianist hits a key that sets up a standing wave in a piano string that is vibrating in its fundamental mode. The string is 0.5 m long, has a mass density of 0.002 kg/m and is held under a tension of 120 N. What is the wavelength...
  34. S

    What is the Wavelength of Earth and its Impact on the Macroscopic World?

    I got this from my grade 12 physics notes. It says that Earth, having a mass of 6.0x10^25kg and a speed of 3.0x10^4 m/s, when plugged into the wavelength equation λ=h/(mu) (where u is speed), has a wavelength of 4x10^-63 m. Then, does this mean it has a frequency of 7.5x10^70 Hz? If so, then...
  35. S

    De Broglie Wavelength Calculation for an Electron with KE= 8.5 eV

    Homework Statement What is the De Broglie wavelength of an electron with KE= 8.5 eV? Homework Equations λ=h/p KE=0.5mv2 p=mv The Attempt at a Solution I converted 8.5 eV into joules: 8/5 eV × 1.602e-19 J = 1.3617e-18 Then used it for KE to solve for v: I got 1729006.11...
  36. L

    DeBroglie wavelength in infinite potential well

    nvm i figured it out. it was not in reference to n=4. equation used would be wavelength = 2L/n Homework Statement An electron is in an infinite potential well of width L. Which is not an allowed deBroglie wavelength for the electron to have when n=4? wavelength(k) = 3L, 2L, L/2, or L/3Homework...
  37. R

    The de Broglie wavelength of molecules

    Homework Statement http://img580.imageshack.us/img580/7492/50177994.jpg The Attempt at a Solution I first attempt part (a) since both parts are similar: (a) I need to know "v" in order to use the following equation to find the de Broglie wavelength: \lambda = \frac{h}{p}...
  38. J

    Long vs Short light wavelength absorption

    Hi all I was reading through an astrophysics book{1} and there I came across this sentence: " A dust cloud can either scatter or absorb light that passes through it. Since shorter wavelengths are affected more significantly than longer ones, a star lying behind the cloud appears reddened...
  39. A

    Double slits experiment, wavelength calculation

    Homework Statement In a double slit experiment with slits 1. 10-5 m apart, light casts the first bright band 3.10-2 m from the center of a screen 0.65 m away what is the wavelength ? Homework Equations dsin(theta) = (m +1/2)lambda, The Attempt at a Solution I think to solve...
  40. A

    Change in wavelength, photon hits a free electron.

    Homework Statement A photon with initial momentum p collides with a free electron having a mass m that is initially at rest. If the electron and photon recoil in opposite directions, what will be the change in the photon’ wavelength? (Hint: use relativistic forms for energy and momentum.)...
  41. H

    Size of a waveguide for a given wavelength

    Let λ be the wavelength of an EM wave in empty space. Let a x 0.5*a be the dimensions of the cross-section of the waveguide. Can I use a = 0.35*λ ? It should be possible, it corresponds to θ = π/4, where θ is the effective angle between the long axis of the waveguide and the direction of...
  42. M

    Debroglie Wavelength: λ & v Proportional?

    According to Debroglie Eq λ=h/mv λ and v inversely proportional to each other.But according to eq v=f*λ they seem to be directly proportional.So what is the actual dependence of lambda on v?
  43. M

    Optical modulator wavelength dependency

    What is the effect of using other than 1550nm light with an (LiNbO3, lithium niobate) electro-optic Mach-Zehnder modulator? Thanks!
  44. J

    How does wavelength change with speed?

    I thought I heard the fact that when you make a particle faster it's wavelength get's bigger, and if we accellerate a baseball enough it's wavelength goes visible? but is that just a misunderstanding and opposite... because one can see in the broglie wavelength equation: λ = h/mv that...
  45. J

    How close must the wavelength of a photon be for an atom to absorb it?

    When a photon has a wavelength close to the energy needed for an electron jump in an atom, the atom will absorb the photon. How close must the wavelength be to the energy required for the atom to still absorb it?
  46. V

    Dependance of radiation properties on wavelength

    Do the absorptivity, reflectivity and transmissivity of a surface depend on the wavelength of the incident light?
  47. Q

    Light, Wavelength, Space, and the color of Stars

    Question 1: http://i.minus.com/iOmQvqhasiXmx.png My reasoning is curves 3 and 4. These curves have the biggest relative brightness of orange. Question 2: Stars are called blackbody radiators because they a) never appear perfectly black b) always appear perfectly white c)...
  48. edpell

    De Broglie wavelength and direction

    We can calculate a de Broglie wavelength for a particle with momentum p. My question is does this apply to the lateral size of the particle? Perpendicular to the motion the momentum is zero. What can we say about the size of the particle in the perpendicular direction?
  49. R

    De Broglie Wavelength: Homework Question Solution

    Homework Statement The Attempt at a Solution I don't see how they got sqrt(1.5/E) I tried it like this Not the right answer.
  50. W

    Calculating Wavelength and Identifying Color Using Young's Apparatus

    Homework Statement a certain young's apparatus has slits 0.12 mm apart. the screen is at a distance of 0.80 m. the third bright line to one side of the centre in the resulting interference pattern is displaced 9.0mm from the central line. calculate the wavelength of the light used. What...
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