Friday, January 30, 2015

Millikan Oil Drop Method to determine Charge of Electron

We can calculate the charge on the electron basing on Millikan’s oil drop experiment. Between the two circular identical plates oil drops are sprinkled through a device called atomizer. The purpose of this device is to produce very small oil drops.

On the oil drop there are multiple forces acting. Weight is the force that is always acting in the downward direction, up thrust is the force that always acts in the upward direction. When the drop starts moving, there is another force called viscous force starts acting against the motion.

Viscous force is similar to frictional force which opposes the relative motion. As the drop starts moving in the downward direction, viscous force also increases in the upward direction. Being the downward force is constant and the upward force is steadily increasing, at a particular stage these two forces are going to be balanced with each other. At that instant the drop acquires a constant velocity and the velocity is called as terminal velocity.

The oil drops during the motion acquires a positive charge due to friction. If a electric field is applied in the upward direction, the drops starts experiencing a new electric force in the upward direction.

Again at the equilibrium state, the drop will acquire a different terminal velocity and by combining both the cases we can derive the equation for the charge.

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