CIE Abstract

Background
     The quantification of charge was first confirmed  by Robert Millikan in 1909 (which also gave the charge of an electron). This was accomplished through his now-famous oil-drop experiment, in which he used an electric field between a metal plates to balance the force of gravity acting on a charged droplet of oil. This placed that droplet in a state of suspension between the two plates in the electric field. thereby making it's weight, the buoyant force and the product of the electric field and it's charge the only forces acting on it. This made it possible to quantize the charge. A variation of this experiment, which was conducted in the hope of verifying Millikan's original results, is reported here.

Results

     Small nylon balls were used in lieu of the oil used in Millikan's original experiment. These nylon balls were dropped into a metal capacitor that was being charged by a five-thousand volt power source. Rather than floating as the droplets did in the experiment from the early 1900's, the nylon ball fell to the bottom of the capacitor, at which point it was given a charge through the application of air resistance. This caused the ball to accelerate upwards into the higher plate in the capacitor, at which point it remained in contact of that plate. The voltage running through the system was regulated by a potentiometer that can vary by millions of ohms. The distance between the plates and voltage difference were measured to be about 1.0 cm and 1000V/cm respectively. These values were then used to calculate the electric field causing the nylon ball to accelerate toward the top plate. The acceleration of the nylon sphere was determined using a high speed camera. This led to the values of all of the forces acting on the sphere and ultimately the charge of an electron.
     After building the apparatus and taking measurements, the experiment yielded values that were within a reasonable margin of the values that Millikan acquired.

Conclusion

    By imparting an acceleration on the nylon ball it was possible to analyze the electrical forces involved in this acceleration using F(electric)-Mg = Ma with f (electric) being F(electric) = qE. {Having a known E field mass and acceleration, it was possible to determine the charge.} After multiple trials a factor was determined which all the different charges were multiples of, which is the charge of a single electron. This experiment resulted in a values within X% of the accepted value of the charge of an electron, Blah. It was pretty solid.

Progress with Prototype

10/24/12    Today we set up the first prototype we tried using various oils but we could not make out any distinct  effects on the drops. When trying to use the microscope to see the drops we took about 20 minutes trying to get it in focus but with not much success. With this we decided to try using the nylon ball. We used a funnel to get the ball through the plates. When dropping the ball through  the field the ball fell straight to the plate without bouncing, as it did when the plates weren't charged. But we were unable to  get the ball todo anything other then drop.

10/23/12     We decided to buy a 1M ohm potentiometer as well as some 10M ohm resistors. When using this we broke the dielectric of air. We solved this by increasing the voltage using the resistor. But the ball still wouldn't move. In order to remove the ball from between the plates we blew the ball out but instead of leaving the plates the air passing over it ionized the ball and made it oscillate as shown below.

Quick Prototype

     In order to meet the competition deadlines we have decided to make a smaller and quicker prototype. This will give us data to analyze and hopefully it will be accurate enough for us to get decent result when entering our abstract.

    We are planning on using 2 metal plates of sheet metal the first plate will be supported from the ground by a glass. The second plate will be supported by small insulators simply placed on top of the first plate. The top plate will have a hole drilled in the top. For an atomizer for the oil we will simply use a spray bottle.

The following image is an actual preliminary representation of the apparatus. The two small plates are connected in series to the power supply. The power supply itself is able to deliver (in theory) 5000 volts without any regulation. In order to manipulate it we, added a 10,000 Ohm resistor which will regulate the power delivered to the plates which will act as a capacitor. A nylon ball will fall through the hole on the top plate. It will then levitate given enough electric force.

Another variation to the device is the implementation of optical lenses consisting of a cross-hairs lens and a augmentation lens. For this version, instead of using a nylon ball, particles of oil will be sprayed through the hole by an atomizer. A light source (not shown) will display better the behavior of the particles.

Research Results

     Ionization: The ionization could be done by using alpha particle emitters available at school. However, some sources say that the friction from the liquid coming out of the atomizer will ionize it. For now we will try and not use radiation due to the simplicity but if it becomes necessary to ionize the dropping particles then we will use the radiation available to us. Most likely alpha particles emitted by Thorium 232 or a similar source of radiation since alpha particles are more available and slightly safer.

     Oil: The type of oil used in the original experiment was clock oil. This is the type of oil we will look into using. An alternative is small nylon balls (about 1/8 or 3/32 of an inch in diameter) the advantage to these is it would be easy to find the mass and volume of the ball and they could be reused if needed.

     Plates: The plates can be made of just about any metal and it will work with the voltage needed.

     Voltage: Research showed that a voltage of around 1000V/cm will be required.

     Insulator: The insulator can be glass, wood or cork, or anything that is a decent insulator.

     Microscope: The need to see the drops should be around 2.2 fold magnification

     Light: The light should be strong and concentrated. Maybe an LED.

Research Assignments

The basics of the apparatus needed are known. It should look something like the picture shown below.

We must research all the materials going into this. We need to know how much voltage will be required and the type of material that can handle that voltage. We will also need to know what kind of insulator will be available and appropriate for this experiment. Ionization is essential to this experiment so various forms of radiation will also be studied. This experiment was done before with water (it was not very accurate) but the pressure at which water evaporates became a problem for the data collected so it is necessary to find an oil with physical properties ideal for these conditions. Here is how we spit up the research:
     There will also be a poster board competition coming up in a few weeks that we would like to take place in. It is the CIE poster board presentation. In order to make the deadlines a timeline is shown above was made

Introduction

     The Mt. San Antonio College's Society of Physics Students have decided to recreate Millikan's Oil Drop Experiment in order to verify the charge of an electron.The students working on this project are David Bruns, Cesar Bazua, Jesus Oropeza and Manuel Castaneda. In Millikan's experiment he created an apparatus that atomized a certain type of oil that fell between two plates with an electric potential difference between them. The oil drops were ionized (given a charge) via x-ray radiation and due to this charge would levitate or accelerate upwards. This was recorded and the charge of an electron was discovered. Before this it was uncertain that charge was quantified (that all charges were integer multiples of a basic charge).
     We hope to reproduce similar results given the resources provided at Mt. SAC.