Part One
Questions
1)Calculate the excess pressure inside drops of water of radius 10-7 and 10-8m respectively. Take = 73 mNm-1 and T = 298K.
2) What pressure would be necessary to blow capillary water at 298K out of the pores of a sintered glass filter with a uniform pore diameter of 0.2mm. (g = 73 mNm-1).
3)explain why water vapour will condense in narrow capillaries when the partial pressure of water is below that of the saturation partial pressure of water?
4)Gortex is breathable and waterproof. The active component is a porous PTFE membrane with holes of 700 molecules. Assuming this corresponds to circular holes 100nm diameter, calculate the water pressure that this fabric could sustain without leaking.
5)Considering the saturated vapour pressure of water at the normal body temerature (37C) estimate the temperature at which water WILL condense in the pores of Gortex.
Past Papers
1999 paper 1
20(a)
(also derive the Kelvin Equation)