InterviewSolution
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InterviewSolution
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A certain number of spherical drops of a liquid of radius `r` coalesce to form a single drop of radius `R` and volume `V`. If `T` is the surface tension of the liquid, thenA. Energy `=4 VT [(1)/(r)-(1)/(R)]` is releasedB. Energy `3 VT[(1)/(r)+(1)/(R)]` is absorbedC. Energy `=3 VT[(1)/(r)-(1)/(R)]` is releasedD. Energy is neither relesed nor absorbed. |
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Answer» Correct Answer - C Let there be n small drop each of radius r, which when coalesce from a big drop of radius R. Then `V=nxx(4)/(3)pi r^(3) =(4)/(3)pi R^(3)` or `n=(R^(3))/(r^(3))` Energy released = surface tension x decrease in surface area `=T[4pi r^(2)xxn-4pi R^(2)]` `=T[4pi r^(2)xx(R^(3))/(r^(3)) - (4pi R^(3))/(R)]` `=3T[(4)/(3)pi R^(3)xx(1)/(r) - (4)/(3)pi R^(3)xx(1)/(R)]` `=3T[Vxx(1)/(r)-Vxx(1)/(R)] =3VT[(1)/(r) - (1)/(R)]` |
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