# Why Did Water Droplets Fail to Suspend in Millikan's Early Experiment?

• krbs
In summary, Millikan's initial use of water droplets in his experiment resulted in difficulties in suspending them due to their small size causing them to evaporate and rise as a gas. This made it difficult to accurately determine the mass and charge of the droplets, leading to skewed results. Eventually, Millikan switched to using oil droplets and was able to determine the elementary charge with more accuracy.
krbs

## Homework Statement

When Millikan first performed this experiment, he used water droplets instead of oil. He found he could not suspend the droplets; they would start to move up. Why did this happen?

N/A

## The Attempt at a Solution

The water droplets would have been so small that they evaporated and rose as a gas. The gravitational force wouldn't be strong enough to hold the gas particles in place.

Could you describe to me Millikan's experiment once? I mean, in your own words.

Oil was sprayed through an atomizer into an initial chamber, which gave the oil a charge. A droplet of oil would drip through a hole in the bottom of the chamber into a second chamber separated by two horizontal parallel plates. He could adjust the potential difference between the plates so that the electric force on the oil balanced out with the force of gravity acting on it (net force zero.) The mass of the droplet was found by finding the terminal velocity of the oil after shutting off the power supply. He could then determine charge by setting electric force equal to the force of gravity and solving for charge. He determined that the smallest charge measured was 1.6 x 10^-19 C and that all of the charges measured were multiples of this base charge. Thus elementary charge was determined.

The water droplet would have gradually evaporated, reducing its mass. This would make it difficult to suspend because he'd have to keep adjusting potential difference between the plates. Determining charge would be difficult because he couldn't be certain of the mass. He probably couldn't determine a precise terminal velocity of the droplet either because he couldn't be certain what position it fell from. The results would be skewed because the measurements were so imperfect.

## 1. What is the purpose of the Millikan oil drop experiment?

The Millikan oil drop experiment was conducted to measure the charge of an electron, and to confirm that electric charge is quantized, meaning it only exists in discrete amounts. This experiment provided important data for the development of the atomic model and the understanding of electricity.

## 2. How does the Millikan oil drop experiment work?

The experiment involved suspending tiny oil droplets in an electric field between two charged plates. The droplets were then observed and their motion was measured under different electric field strengths. By comparing the motion of the droplets, the charge of an electron was able to be calculated.

## 3. Who conducted the Millikan oil drop experiment?

The Millikan oil drop experiment was conducted by American physicist Robert A. Millikan in 1909. He received the Nobel Prize in Physics in 1923 for his work on the experiment.

## 4. What were the results of the Millikan oil drop experiment?

The experiment determined the charge of an electron to be approximately 1.6 x 10^-19 coulombs. This value is still used in modern physics and is considered a fundamental constant. It also provided evidence for the quantized nature of electric charge.

## 5. How did the Millikan oil drop experiment impact our understanding of the atom?

The experiment provided evidence that atoms are made up of even smaller particles, including electrons with a specific charge. This helped to develop the atomic model and our understanding of atomic structure. It also confirmed the existence of subatomic particles, leading to further advancements in the field of particle physics.

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