The Tyndall effect is observed only when following conditions are satisfied :
(a) The diameter of the dispersed particles is much smaller than the wavelength of the light used.
(b) The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
(c) The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude.
(d) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.
(a) The diameter of the dispersed particles is much smaller than the wavelength of the light used.
(b) The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
(c) The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude.
(d) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.
- (A)(a) and (d)
- (B)(b) and (d)✓ Correct
- (C)(a) and (c)
- (D)(b) and (c)
Answer: (B)
Solution
The Tyndall effect shows up only when colloidal particles actually scatter the light. That calls for particle diameters comparable to the wavelength, not far below it, and it calls for the dispersed phase and the medium to differ sharply in refractive index so their boundaries scatter strongly. Those two conditions, the comparable particle size and the large refractive-index mismatch, are the ones that must both hold.
JEE Main · 2017 · 02 Apr 2017 · Offline · Single correct option