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I Experimental Demonstration of the Raman - Nath Effect

  1. Dec 2, 2017 #1
    I want to design an experiment to demonstrate Raman - Nath effect.

    Due to limited resources at my hand (my school doesn't have too much resources), my condition is somewhat like Raman, and hence I want to do the original experiment that Raman and Nath conducted in IISc Bangalore back in the late 1900s.

    The diagram of the experiment is this:

    Raman - Nath effect.png

    As you can see, laser from the left will go through the liquid kept in the cylinder. There will be a sound source below the cylinder, which will create sound of same frequency but different amplitudes, so as to create fluctuations in the density of the liquid, which will affect the optical density, and thereby diffract the incoming beam, which will create a diffraction pattern on the screen.

    I have all the things mentioned above except the sound source. I had first decided to use a resonance box, so that I can make a resonance by vibrating a tuning fork of the same frequency, and holding it near the box. With this system, I could even vary the amplitude of the wave as I want by hitting the fork hard or soft. But i found that my school doesn't have the resonance box.

    I searched on the net to see if I could buy one, but the only one on Amazon is a bit expensive (about $80, which amounts to 5120 INR).

    Does anyone have an idea that could help me out of this situation? This is the only problem that I am facing.
  2. jcsd
  3. Dec 2, 2017 #2

    Charles Link

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    Suggestion is to create the sound with an electric guitar string that comes with an amplifier/speaker system. I think you would want the sound to travel mostly in one direction, so it would help to confine the sound from the speaker somehow.
  4. Dec 2, 2017 #3
    Excellent idea. But the problem is that, neither do I have a guitar, nor do I know how to play it.

    Your mention of speakers or amplifiers reminded me of something. There is one app: Physics Toolbox Tone Generator that I can use. Moreover, it provides options to vary frequency by small to large amounts, change waveform and the harmonics. So I'll use that.

    Thanks anyways. :smile:
  5. Dec 5, 2017 #4
    A setup with a guitar or any human-audible sound waves will not give good results. At the highest frequencies of about 10 kHz, and a sound velocity in water of about 1500 m/s, the wavelength is 15 cm, and that will be the order of the grating spacing. If we now use the standard equation for diffracion, d sinθ = mλ, the angle of diffraction is much too small to be measured. The standard experiment uses ultrasound at frequencies around 10 MHz.
  6. Dec 5, 2017 #5

    Charles Link

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    Thank you @Chandra Prayaga I have had some experience with the Raman-Nath effect, but that was quite a number of years ago, and yes, the frequencies that were used were in the low MHz region. We worked with piezoelectric transducers if I remember correctly, and they are not very expensive, but also not inexpensive. I believe the waves they generate can come in two forms=bulk waves and surface waves. @Wrichik Basu You may want to google "acousto-optic" devices and see what is commercially available.
  7. Dec 5, 2017 #6
    @Chandra Prayaga thanks for the pointing that out soon enough, otherwise I would have had to face some difficulties in school if I had already told the lab assistants to make arrangements.

    @Charles Link commercial devices? I cannot afford it in any way. Maybe I've to wait to do the experiments till I enter college. :headbang: :cry: :H
  8. Dec 5, 2017 #7
    You are welcome.
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