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The programme examines the dual particle/wave nature of electrons and photons. The unifying nature of the de Broglie relationship is brought out.
Metadata describing this Open University video programme
Module code and title: S101, Science: a foundation course
Item code: S101; 29
First transmission date: 25-09-1979
Published: 1979
Rights Statement:
Restrictions on use:
Duration: 00:24:00
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Producer: John Stratford
Contributors: Mike Pentz; Russell Stannard
Publisher: BBC Open University
Keyword(s): Bubble chambers
Subject terms: Diffraction; Electrons; Momentum; Photons; Physics
Footage description: Shots of diffraction rings and bubble chamber photos. Mike Pentz introduces the programme. Mike Pentz puts several diffraction gratings in front of a laser and examines the resulting diffraction patterns. Russ Stannard with a cathode ray tube. He explains flow electrons are emitted inside the tube and are directed at a fluorescent screen at the front. Stannard, by holding a magnet to the screen, shows that the electrons which appear on the screen really are charged particles. Stannard goes on to demonstrate a cathode ray tube in which a thin foil of graphite has been placed between the electron gun and the screen. An animation shows how the crystalline arrangement of the graphite results in the diffraction pattern seen. Stannard next demonstrates the effect, on the diffraction patterns, of changing the voltage of the electron gun. He points out that as voltage increases so the wavelength decreases. From this he derives the de Broglie relation. Pentz uses a magnet to demonstrate that the diffraction patterns on the cathode ray screen are really produced by electrons. Russ Stannard collides ball bearings on a table to demonstrate the behaviour of particles when they collide with other particles. He then examines a bubble chamber photograph and explains how bubble chambers can be used to see if electrons behave like any other particles during collisions. Pentz briefly sums up the wave/particle duality of the electron. He then does an experiment with an electroscope which suggests that light also has a wave/particle duality. Russ Stannard collides more ball bearings on a table to show the effect on particles of various angles of deflection during collision. This gives a clue to a method for measuring conservation of momentum of particles. In order to discover if photons exhibit conservation of momentum properties as do particles, Stannard performs an experiment which scatters gamma rays at various angles of deflection. Photons are emitted during the collision and their scatter is plotted on a cathode ray screen. Stannard goes on to derive the de Broglie equation from the experiment above. He writes on a pad as he talks. Mike Pentz, with a caption of the de Broglie sums up the way in which the equation links the wave and particle properties of both electrons and photons. Finally, Russ Stannard simulates a situation in which only a single photon in a diffraction experiment arrives on the screen at a time. A diffraction pattern is slowly built up.
Master spool number: HOU3127
Production number: FOUS029E
Videofinder number: 1204
Available to public: no