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I would like to build a ripple tank but I don't really know if I need a fresnell lens to make the projection or not, and why would it be needed in case it does?

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  • $\begingroup$ what kind of extended light source will you use? $\endgroup$
    – trula
    Commented Nov 26, 2019 at 11:57
  • $\begingroup$ @trula A simple lamp. A lantern. Maybe I don't understand the question $\endgroup$
    – Swike
    Commented Nov 26, 2019 at 14:09

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The ripple tanks I've used did not have Fresnel lenses. They had a light source that was designed to be pointlike. In one design, there was an incandescent bulb with a straight filament, and you would orient the filament vertically, so that from underneath it would appear as a point source. In the other design, they used a small LED.

Typically these designs work well if you have about a meter worth of vertical space, so that the object and image distances can be big enough to form a real image with waves of a typical amplitude (which act like lenses).

Make sure you have an effective way to prevent reflection from the sides of the tank, e.g., using sponges.

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