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Transverse and longitudinal waves

  1. Feb 14, 2014 #1
    let me make it clear this is NOT A HOMEWORK.i am just having a doubt.
    if there is a rope passing through two parallel vertical slits placed close to each other. The rope is fixed and if it's moved up and down perpendicular to its length,transverse waves are generated with
    vibrations parallel to the slit.But if the second slit is made horizontal, the two slits are perpendicular to each other. Now, no vibrations will pass through the second slit and amplitude of vibrations will become zero.but how is that possible?:confused:

    On the otherhand, if longitudinal waves are generated in the rope by moving the rope along forward and backward, the vibrations will pass through them irrespective of their positions.

    why only longitudinal waves exhibit this behaviour
  2. jcsd
  3. Feb 14, 2014 #2


    Staff: Mentor

    The phenomenon you are describing is called polarization. It is one of the distinguishing features of transverse waves that they have two polarization states and one of the distinguishing features of longitudinal waves that they have only one. That is why light waves were known to be transverse long before Maxwells equations.
  4. Feb 14, 2014 #3


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    What you have already written, more or less contains the answer to your question. It's only when you have a transverse vibration that there is any vibration away from the direction of propagation. If there is no transverse component of movement (i.e. in a longitudinal wave) then you cannot select a particular transverse 'component' in order to polarise the wave.
    BTW, the rope example makes it hard to deal with the general question of polarisation at 'any angle'. It is better to consider the familiar radio (dipole) antenna, which launches waves that are polarised in the direction of the 'rods' of the antenna. A similar receiving antenna, parallel with the rods, will pick up a maximum signal. As you rotate the receiving antenna, you will pick up less and less of the signal (just receiving the component in line with the receive antenna), until you are at right angles, where there is zero component. It's an example of Vectors.
  5. Jan 20, 2016 #4
    will not the amplitude of longitudinal wave become zero if it passes through vertical slit
  6. Jan 20, 2016 #5


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    Why should it? The slit will reduce the total flux of energy (of course - because most of the energy would be blocked by the plate with the slit in it) but that would be the case for a transverse wave too. The only particle motion will be 'through' the slit if the wave is longitudinal. Check your definitions of the different waves; that could be your problem.
  7. Jan 25, 2016 #6
    in case of transverse waves as the horizontal slit rdeuces its amplitude to zero why the vertical slit donot reduces the amplitude of longitudinal waves to zero and transerve wave will pass through the vertical slit unobstructed but the longitudinal wont
    the transverse wave amplitude will be zero by the horizontal slit so can"t the vertical slit zero amplitude of the longitudinal wave
    Last edited: Jan 25, 2016
  8. Jan 25, 2016 #7


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    neither the vertical or horizontal slits will stop the longitudinal wave because neither of them are in the plane of the
    oscillation of the longitudinal wave
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