# The Millikan Oil Drop Experiment (calculating e given a series of charges)

• bhimberg
In summary, the goal of this lab is to calculate the constant e (1.602e-19 C) by determining the terminal velocity of an oil drop under the influence of both gravity and an electric field. The equations used are W = W(v2/v1), where v2 is the terminal velocity with the electric field, v1 is the terminal velocity without the electric field, W is the weight of the oil drop, E = V/d is the electric field, and q=W(v2/v1 + 1)d/V is used to solve for the charge. The values found for three drops are 4.678E-16, 6.367E-16, and 4.32616E-16,

## Homework Statement

This is a lab, where we have to calculate the constant e (1.602e-19 C) by calculating the terminal velocity of an oil drop while under the influence of gravity, and the terminal velocity while under the influence of gravity and a known electric field.

## Homework Equations

Eq - W = W(v2/v1), where v2 is the terminal velocity with the E field and v1 is without. W is the weight of the oil drop (mass * gravity of the drop), E = V/d is the electric field. Solving for q:

q=W(v2/v1 + 1)d/V

Weight is calculated with a series of other equations.

## The Attempt at a Solution

The goal is to ?quantitize? the charge found on a series of drops. I found the charge for three drops to be:
4.678E-16, 6.367E-16, 4.32616E-16

These values must be some value x multiplied by an integer n, where x will turn out to be 1.602e-19 C. The problem is I don't know how to find this value given 3 values of charge for three different oil drops. Also, these seem to be very large numbers. These oil drops are very small, and in the lab they should typically vary between n=1 and n=10, from what I've read. So what should I do? If you plot three functions from the above, they are just contours and so don't cross.

Is this a problem that I don't understand how to solve, or have I made an error somewhere? Thanks for any help.

I would suggest that you first review your experimental procedure and make sure all measurements and calculations are accurate. The values for the charges you have obtained seem to be much larger than the expected range for oil drops. It is important to ensure that your equipment is properly calibrated and that all external factors, such as air currents, are controlled for.

Once you have verified the accuracy of your data, you can use the Millikan Oil Drop Experiment to calculate the value of the elementary charge, e. This experiment is based on the principle that the charge on an oil drop is quantized and can be expressed as an integer multiple of the elementary charge. By measuring the terminal velocities of the oil drop under different conditions, you can use the equations provided to calculate the charge on each drop.

To find the value of e, you can plot a graph of the charges you have calculated against the number of charges on each drop. The slope of this graph should give you the value of e. If your data is accurate, the slope should be close to the expected value of 1.602e-19 C.

If your data does not yield a satisfactory result, it is possible that there may be external factors affecting your measurements. In this case, it may be necessary to repeat the experiment with more careful control of variables. Additionally, it is important to note that the Millikan Oil Drop Experiment is a delicate and challenging experiment, and it is not uncommon for there to be some discrepancies in the results. As a scientist, it is important to carefully analyze your data and consider all possible sources of error before drawing any conclusions.

## 1. What is the Millikan Oil Drop Experiment?

The Millikan Oil Drop Experiment is an experiment conducted by physicist Robert Millikan in 1909 to measure the fundamental unit of electric charge, also known as the electron charge (e). This experiment played a crucial role in accurately determining the charge of an electron and further confirming the existence of subatomic particles.

## 2. How does the Millikan Oil Drop Experiment work?

The experiment involves measuring the rate at which tiny oil droplets, suspended in a chamber by balancing the forces of gravity and air resistance, fall through an applied electric field. By varying the electric field, Millikan was able to calculate the charge on each individual oil droplet and determine that it was a multiple of the electron charge, thus accurately determining the value of e.

## 3. What equipment is needed for the Millikan Oil Drop Experiment?

The equipment used in this experiment includes an atomizer to create small oil droplets, a microscope to view the droplets, and a charged metal plate to create an electric field. Other necessary items include a source of X-rays to ionize the air, a power supply to control the electric field strength, and a timer to measure the rate at which the droplets fall.

## 4. What are the limitations of the Millikan Oil Drop Experiment?

Despite its significance and accuracy, the Millikan Oil Drop Experiment has some limitations. It assumes that the oil droplets are perfectly spherical and have a constant mass, which may not always be the case. Additionally, the experiment relies on the assumption that the charge on the droplets is a multiple of the electron charge, which may not always be true.

## 5. How is the value of e calculated from the results of the Millikan Oil Drop Experiment?

The value of e can be calculated by dividing the charge on an oil droplet by the total number of charges on it, as determined by varying the electric field. The average of these values is then taken to be the charge on a single electron. The value of e obtained from this experiment is 1.602 x 10^-19 coulombs, which is the same as the currently accepted value.