Available online
Description
The programme is a case study on the electron microscope; a device which uses many of the fundamental electromagnetic principles discussed in the first four course units.
The programme is a case study on the electron microscope; a device which uses many of the fundamental electromagnetic principles discussed in the first four course units.
| Module code and title: | TS282, Electromagnetics and electronics |
|---|---|
| Item code: | TS282; 04 |
| First transmission date: | 04-03-1972 |
| Published: | 1972 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:34 |
| + Show more... | |
| Producer: | Michael Weatherley |
| Contributors: | Peter Chapman; Fred Sheldon |
| Publisher: | BBC Open University |
| Keyword(s): | Case study; Electromagnetic principles; Electron microscope; Electron vacuum; Magnetic fields; Models; Resolution; Wave concept |
| Footage description: | P. Chapman introduces the programme. He has before him the elements of an optical microscope. Chapman points out each component and explains its function. Chapman places a diagram of an electron microscope next to the above components. He points out the corresponding component for each function in both. Chapman standing next to an electron microscope. He points out its component parts and relates these to the schematic diagram which he used above. Chapman explains why the microscope must operate under a vacuum and why a magnetic shield is needed. He then explains how the magnetic lenses are focussed. Fred Sheldon removes the electron gun from the electron microscope at Cambridge University. Shots of electron gun filament and its focussing shield. Shots of 2 micrographs at same magnification. One was taken with an optical microscope, the other with an electron microscope. Chapman uses these pictures to explain that it is resolution rather than magnification which is important for seeing detail. Chapman explains what is meant by resolution in microscopy. He uses diagrams of a light wave and an electron wave as an aid. Chapman then explains that because of the wave properties of electrons, the ball bearing analogue for electrons will not work in this situation. Fred Sheldon focusses the electron microscope at Cambridge University. Shots of the instrument's final viewing screen shows the process. Chapman with a magnetic focussing lens cut in half. He explains why magnetic rather than electrostatic lenses are used in electron microscopes. Chapman draws a diagram to aid his commentary. Chapman explains what type of magnetic lenses are required. A schematic diagram of a solenoid showing lines of flux density is used as an aid. Chapman with a diagram of a magnetic lens. Lines of flux density are again shown. He explains what happens to electrons as they pass through the flux. Chapman with a model of a magnetic lens. Flux lines and electron path lines are shown. He explains how the path of the electron is modified and, by Fleming's Left Hand Rule, in what direction. Chapman uses a two dimensional diagram of electron paths through a magnetic lens. The diagram shows how the electron beam is focused and how focus is changed. Shots of the final viewing screen of an electron microscope. The beam is not centred on the axis of the lens. Deflection correction centres the beam. Shots of electron microscope image of a metal grid showing the rotating effect of magnetic lenses. Chapman with a simple schematic diagram of the electron microscope showing the magnification at each lens. As an example of magnifying power he explains that a small metal grid 3mm. in diameter would be 2 miles across at full magnification of the electron microscope. Chapman shows how a speciman is mounted for electron microscopy. Sheldon places a specimen into the microscope. Shots of a crystal specimen at various magnifications up to 50,000. Chapman uses a model of the silicone crystal lattice to explain how electron microscopy can sort out atomic structures. Shot of silicone electromicrograph. The lattice lines are clearly visible. Chapman explains how specimen are tilted in the microscope. Shot of crystal specimen being tilted. Results seen on final viewing screen. |
| Master spool number: | 6LT/70342 |
| Production number: | 00521_2104 |
| Videofinder number: | 3589 |
| Available to public: | no |
