Holmarc's Millikan oil drop apparatus (Model No: HO-ED-EM-01) is modernized version of classic set-up used to find out electron charge. The apparatus makes use of CCD camera along with computer screen for convenient viewing of oil droplet. Measurements of the droplets are also taken from display screen using a software module. Control of high voltage power supply across the electrode is made easy by having a digital display on the front panel.
The apparatus consists of two horizontal metal discs placed 10mm apart in a closed chamber. Non-volatile oils are used for the experiment. A bright LED is used for illuminating the droplets inside the chamber in order to get a clear view.
The significant difference in our setup is in the imaging system used for the observation of droplet movement. We use USB 2.0 camera which can be directly connected to the PC to monitor the droplet movement and can measure the velocity of the droplet with the help of Holmarc's dedicated software. This makes the measurements much easier and eliminates the need for conventional telescope and stopwatch system. A variable power supply of 0-2KV is used for conducting the experiment. The temperature inside the drop viewing chamber can be monitored through the front panel display system.
Charge of an electron can be obtained from this relation,
q = ( ( V2 / V1 ) + 1 ) [ ( 4 / 3 π r3 ) ( ρ - ρair ) g d ] / V
V1 - Terminal Velocity
V2 - New Terminal Velocity
r - Radius of the Drop
ρ - Density of Liquid
ρair - Density of Air
g - Acceleration due to Gravity
d - Distance between the Plates
V - potential Difference