Measuring the Viscosity of a Liquid

The viscosityof a liquid can be measured using the apparatus below.

The rate of flowof a liquid of viscositythrough a pipe of circular cross section with radiusand lengthis given bywhereis the pressure difference between the ends of the pipe. For the apparatus abovesoRearranging this gives

The internal radiusof the tube can be measured accurately with a travelling microscope and the experiment is left to run until the liquid is dripping at a steady rate.

To ensure accuracy note the following:

It must be dripping and not pouring since use of the equation above requires that the kinetic energy of the water exiting the pipe is minimized.

Viscosity varies with temperature, so the temperature must be constant throughout the experiment.

No evaporation of the liquid must be allowed after it has dripped from the tube, else the liquid flow rate will not be accurate.

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