Determination of capillary radius by flow measurement, one method for determining the radius of a capillary tube is by measuring the rate of flow of a Newtonian liquid through the tube. Find the radius of a capillary from the following flow data: 

Length of capillary tube                                       50.02 cm 

Kinematic viscosity of liquid                               4.03 x 10^–5 m²/s 

Density of liquid                                                   0.9552 x 10³ kg/m³ 

Pressure drop in the horizontal tube               4.829 x l0⁵ Pa 

Mass rate of flow through tube                         2.997 x 10^–3 kg/s 

What difficulties may be encountered in this method? Suggest some other methods for determining the radii of capillary tubes.