MEASURING e USING THE MILLIKANAPPARATUS
The charge on the electron is a constant in Physics. This constant was first measured by R.A. Millikan, in 1909-1913, using oil drops. He showed the discreteness of the electron charge as well. Measurement requires balancing the electrical and gravitational forces on the drop. It is possible to use polystyrene spheres which are of uniform radius and density. The mass can be checked from the relationship of the gravitational forces and the viscous forces on a sphere in free fall. The Boltzmann constant can be estimated by the dispersions in the time of the free fall.