How does the dark and bright fringes form ?

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SUMMARY

The formation of dark and bright fringes in a ripple tank is a result of the interaction of water waves with light, resembling the effects of convex and concave lenses. When viewed from below, crests of the waves act like convex lenses, focusing light into bright fringes, while troughs behave like concave lenses, dispersing light into dark fringes. The sensitivity of the human eye to variations in brightness enhances the visibility of these patterns. The depth of the water relative to the focal lengths of the curved surfaces plays a crucial role in determining the appearance of these fringes.

PREREQUISITES
  • Understanding of wave behavior in fluid dynamics
  • Basic knowledge of optics, specifically lens effects
  • Familiarity with the principles of light refraction
  • Experience with experimental setups involving ripple tanks
NEXT STEPS
  • Research the principles of light refraction and how it applies to water waves
  • Explore the effects of wave depth on light patterns in ripple tanks
  • Study the characteristics of convex and concave lenses in optics
  • Investigate the sensitivity of human vision to brightness variations
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Students and educators in physics, optical engineers, and anyone interested in wave optics and fluid dynamics will benefit from this discussion.

yuganes warman
When there is a water wave in a ripple tank( not involving any interference experiment ) there will be a pattern on the bottom of the ripple tank , that is the the dark and bright fringes. How does the bright fringes and dark fringes form for only water waves experiment in ripple tanks ? It involves the convex or concave lense concept, please explain. Thanks
 
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If you look from below, a water wave looks like a bunch of long concave and convex lenses trailing each other. As in, from below, a crest looks like it will collect light into a point, and a trough looks like it should spread out incident light. So you will have some fringes from light being collected (bright) or dispersed (dark).

This is a very rough guess, and I'm no expert, but it seems intuitive. Hope it helps.
 
Yes. It's hard to be any more specific about this but the fact is that the eye is very sensitive to patterns so it is aware of some very slight variations in brightness due to this 'focussing' effect. I think it could go either way (i.e. brighter/darker or darker/brighter) depending on the actual depth of the water relating to the focal lengths of the curved surfaces.
 

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