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Having established that electrons behave as a stream of charged particles, the programme shows how the amount of charge and the mass of the electron and ions were determined by J.J. Thompson and Ro...bert Millaken.
Metadata describing this Open University video programme
Module code and title: S101, Science: a foundation course
Item code: S101; 10
First transmission date: 08-05-1979
Published: 1979
Rights Statement:
Restrictions on use:
Duration: 00:24:00
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Producer: David Jackson
Contributors: Charles Harding; Mike Pentz
Publisher: BBC Open University
Keyword(s): Cathode rays; Crookes paddle wheel experiment; Maltese cross experiment
Footage description: Mike Pentz, standing in a reconstruction of J. J. Thompson's laboratory at Cambridge, introduces the programme. Pentz demonstrates a cathode ray tube of the type used by Thompson in 1897- He explains how the tube works. Pentz goes on the perform the Maltese Cross experiment using another cathode ray tube. He demonstrates the magnetic deflection of electrons in the tube. In order to demonstrate that the electrons in the cathode ray tube are a stream of charged articles, Pentz performs an experiment, first done by William Crookes, who inserted a small paddle wheel into a cathode ray tube. The wheel is turned by the electron stream. Pentz goes on to perform another experiment designed to demonstrate that electrons in cathode ray tubes travel as a beam of charged particles He uses an electrostatic force to shift the beam in a predicted direction. Charlie Harding explains the experiment, conducted in 1909 by Robert Millaken, which determined the amount of charge carried by an electron. He points out and explains the function of the equipment and then goes on to perform the experiment. Pentz briefly asks students to use the data from the Millaken oil drop experiment which is published in the broadcast notes to verify that the charge of the electron is an elementary charge. Pentz explains, with the aid of a cathode ray tube, how J. J. Thompson worked out the ratio of charge to mass of the electron. Pentz goes on to discuss the method used by Thompson to measure the charge to mass ratio of a series of positive ions. He points out that this was really the beginning of what would now be called mass spectroscopy. The principles of modern mass spectroscopy are explained by Pentz who uses a model made up of a ramp, a magnet, and ball bearings of various mass to illustrate his points. Charlie Harding, at University College London, look over the mass spectrometer there and points out some of its components. He goes on to record the mass spectrum of three isotopes of neon gas. The trace is shown on the screen. Mike Pentz sums up the programme.
Master spool number: 6HT/72865
Production number: 00525_1340
Videofinder number: 1185
Available to public: no