The number of particles is given by `n = -D(n_(2) - n_(1))/( x_(2) - x_(1))` crossing a unit area perpendicular to X - axis in unit time , where `n_(1)and n_(2)` are particles per unit volume for the value of `x` meant to `x_(2) and x_(1)` . Find the dimensions of `D` called diffusion constant.

Explanation

(n) = Number of particle passing from unit area in unit time
`= ("Number of particles")/( Axxt) = ([ M^(0) L^(0)T^(0)])/([L^(2)] [ T]) = [L^(-2)T^(-1)]`
`[n_(1)] = [ n_(2)]` = Number of particles in unit volume = `[L^(-3)]`
Now from the given formula ,
`[D] = ([n] [ x_(2) - x_(1)])/([ n_(2) - n_(1)]) = ([L^(-2)T^(-1)][L])/([L^(-3)]) = [L^(2)T^(-1)]`