An experiment to determine ceramic particle sizes

[Tiberious]

Homework Statement

(I) An experiment to determine ceramic particle sizes showed that the rate of descent when suspended in a fluid ranged from 1.2 × 10–6 m s–1 to 5 × 10–6 m s–1. 
The density of the material was 3800 kg m–3 and the density and viscosity of the fluid at room temperature were 1632 kg m–3 and 0.00972 Pas respectively. Calculate the range of sizes of the particles. 


Homework Equations

v= (d^2 (p_s-p_1 )g)/〖18〗_η

The Attempt at a Solution

Im slightly confused on the above equation. Is this the correct equation to be used in this instance. it's the only one I can find from the notes.

 

[mfb]

That has an odd formatting, but it gives a relation between speed and particle diameter where the rest should be known.