Particle 1 and 3 did not last, so they are not included in the calculations.
Some of the droplets had big jumps in the rise times, so we disregarded those data points.
Averages are calculated by taking the accepted data points, summing them up and dividing by the number of points.
Standard deviation is calculated by taking the difference of the data point and the average value, squaring it, summing these results and dividing by the number of trials, then taking the square root of the result.
The main purpose of this lab is to calculate the charge of a single electron. The way to do this is to observe the fall and rise times of many charged drops of oil in an electric field so as to calculate the discrete charge of one electron by noticing that the charge on each oil drop is a multiple of a specific discrete value.
Equipment
PASCO scientific Model AP-8210 MILLIKAN OIL DROP APPARATUS
Power Supply Tel-Atomic (50V and 500V power supply)
2 multimeters, measuring Voltage and Resistance.
Roberts Travel Size (density 886 Kg/m^3) Mineral Oil
Safety
There are a few safety concerns in this lab:
1. Personal safety first:
This device uses Thorium to charge the oil drops, which is a radiation source. Be careful around it and do not leave the source switch open unless charging oil drops.
The voltage is high, 500 volts, and can cause shock. Connect equipment when the power is off, and turn the power supply to the lowest settings before powering it on. Turn on the power, then turn up the voltage to the required level as described in the procedure.
The apparatus has a lamp which uses a wall outlet. Be careful when plugging it in.
2. Safety of the equipment:
Do not set the power to higher than the specified amount, this can cause damage to the device.
There are banana plug ports for measuring the resistance of a thermistor to measure the temperature. Do not put any current through these ports, as it can damage the thermistor.
Setup
Device Placement
Place the device on a steady surface.
Place it high enough so that when you look into the device, you will not be straining your neck or posture, as you will be looking through the eyepiece for extended periods of time.
Balance the device so that it is level. There is a leveling bubble (see image) that when the bubble is in the center, it is leveled. Use the feet of the device to raise the different corners.
Device Preparation
Take apart the droplet viewing chamber (see image) and wash and dry the lid, the housing, the droplet hole cover, the upper capacitor, the spacer, and most importantly the spacer lens.
Make sure to blow the water out of the droplet hole cover.
Measure the plate separation (plastic spacer) with a micrometer.
Dry everything off and reassemble, making sure not to put any dust or finger prints on the lenses.
Device setup
Plug in the lamp.
Connect the power supply to the plate voltage connectors using the banana plugs and put a multimeter to monitor the voltage.
Connect another multimeter to the thermistor connectors to measure the resistance.
Move the ionization source lever to the off position.
Turn on the power supply
Adjust the eyepiece
To adjust the eyepiece, put the positioner pin into the center of the chamber.
With the light on, view the pin, and focus so that you can see the pin clearly, and have a gradient from light to dark from one side of the pin to the other. Do this using the lens focus and the lamp adjuster.
You also want to be able to see the grating that will be used to measure the distance the drop fell.
Take out the pin, and replace the droplet hole cover.
Procedure
Let the device warm up a bit.
take note of the temperature and the voltage
Take the atomizer and spray it onto a paper towel a few times till you feel the resistance of the oil traveling through the atomizer, this means it is primed.
Move the ionization source lever to the 'spray droplet' position.
Look through the eyepiece and spray into the top, and hold it till you see droplets coming down. releasing will make the droplets rise back up because of the vacuum pressure.
Move the ionization source lever to the off position.
Find a droplet that takes approximately 7 to 15 seconds between major gratings.
When one is found, turn on the ionization source lever to the on position for 5 seconds with the voltage off.
Now turn the voltage on and track the drop that you had identified and measure how fast it rises.
Keep track of temperatures and rise and fall times.
Do this as many times as you can with this drop.
Repeat with other drops.
Data
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Calculations
Particle 1 and 3 did not last, so they are not included in the calculations.
Some of the droplets had big jumps in the rise times, so we disregarded those data points.
Averages are calculated by taking the accepted data points, summing them up and dividing by the number of points.
Standard deviation is calculated by taking the difference of the data point and the average value, squaring it, summing these results and dividing by the number of trials, then taking the square root of the result.