Millikan's oil drop experiment : EXP500010
Référence : EXP 500 010
This experiment aims at repeating, in a simplified manner, the historical experiment by which Millikan in 1909 determined the exact value of the electron charge “e”. It consists of studying the motion of a charged oil drop, subjected to the electric field of a parallel-plate capacitor, a white light source and a sighting device. This comprehensive pack is made up of several parts: a laser light source and a sighting device, a mechanical/optical part, as well as a generator/chronometer.
DETERMINING ELECTRON ELECTRIC CHARGE
With an atomiser, spray oil drops in a capacitor made of two light alloy plates. As they pass through two small holes drilled in the plastic holder of the capacitor, some drops will be charged by electrostatic friction.
Once they have penetrated between the two flat capacitor plates, these oil drops are observed through a sighting device. The latter is equipped with a long focus lens to single out the oil drops falling along the capacitor axis and standing out as shiny dots against a dark background. Its eyepiece is engraved to a tenth of a millimetre.
The pack is secured to a base by a telescopic rod designed to set the sighting device at a height suitable for the user. First, we spray oil drops without charging the capacitor plates. Then, once the vortex motion has ceased, we apply a voltage to the capacitor terminals and identify the drop or drops that are blocked by this field (these are the ionised drops).
The voltage ensuring complete immobilisation of the drop is read. Voltage is cut, and at the same time the chronometer
(integrated in the Millikan generator) is triggered. The time required by the drop to cross a certain number of micrometer
graduations is measured.
Oil drop electric charge is determined by calculating its fall velocity. We observe that, according to oil drop size and velocity, this is always a multiple of the electric charge e, the elementary electron charge.
SUBJECTS APPROACHED
»»Measuring electron electric charge
»»Demonstrating electron quantum nature
»»Implementing a sighting device
NECESSARY EQUIPMENT
| Reference | Description | quantity |
| PSD022040 | Milllikan apparatus | 1 | | PSD022065 | Millikan generator | 1 |
|
|
Mon compte
