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# Oil Drop Experiment

## Experiments that prove the charge of a single electron.

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Discovery of the Electron

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### Electrons

An electron is a negatively charged subatomic particle.

The electron is the smallest subatomic particle. What are the names and charges of the other subatomic particles?

### First hints

The first hint that subatomic particles existed was discovered in an experiment by Sir William Crookes involving a cathode ray tube.

How does a cathode ray tube work? What are cathode ray tubes used in?

Crookes fired a beam through the tube and noticed two things which supported his hypothesis that the beam within the cathode ray tube was made up of particles. What did he notice?

### Contributions by J.J. Thomson

Other scientists were able to conclude that the beam which Crookes saw in the tube were indeed particles which were named electrons.

Further investigation by J.J. Thomson involving a cathode ray tube and magnets helped extend the research of electrons.

He determined that electrons were charged particles. What charge do electrons have, and how did Thomson come to this conclusion?

Thomson also calculated a charge-to-mass ratio for the electron stream. What is a charge-to-mass ratio? What is the value of the charge-to-mass ratio?

### Oil Drop Experiment

Robert Millikan conducted a series of experiments known as the oil drop experiment to determine the mass and charge of an electron.

What is the accepted value for charge on an electron today? How close was Millikan to this value?

For gudiance in answering the above question, or for more information in how Millikan conducted his experiment, look here.

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