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I am JEE student in India and while I'm reading my chemistry book (NCERT class12), there mentioned a point that "the refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude for colloids (in Tyndall effect)" But to happen scattering effect, the photons in the light must dash the atoms of colloids(like in Rutherford's model) and creates a scattering spectrum of shades of light (Tyndall effect) on the screen, so if refractive indexes are different it will end in a scattering of light(Reflection within itself) within itself(colloidal solution ) and will not let any light photons to scatter out so my convention is that the refractive indexes must be same through like a rectangular glass slab to scatter the light out. Is my convention is a misconception? If, please help me with it...dispersion in rectangular slab, tyndall effect

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The geometrical optics approach is only valid over distances much larger than the wavelength, not over the (sub-micrometer) sizes of colloids. At these small scales, one can no longer describe light as a ray that enters the particle and remains trapped due to the high local index (if I understand your concern).

You can see the solution as having a homogeneous average refractive index, so the incoming beam propagates according to the reflection/refraction laws, on top of which there are highly localized variations due to the colloids, which scatter light as in your second diagram.

Of course, since energy is conserved these scattering events lead to an attenuation of the primary beam as it goes through the medium.

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