Available online
Description
This programme shows how the concept of magnetic flux, as discussed extensively in the unit, can be used to explain the behaviour of magnetic circuits.
This programme shows how the concept of magnetic flux, as discussed extensively in the unit, can be used to explain the behaviour of magnetic circuits.
| Module code and title: | TS282, Electromagnetics and electronics |
|---|---|
| Item code: | TS282; 03 |
| First transmission date: | 19-02-1972 |
| Published: | 1972 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:21 |
| + Show more... | |
| Producer: | Michael Weatherley |
| Contributors: | Peter Chapman; Alan Cooper; John Sparkes |
| Publisher: | BBC Open University |
| Keyword(s): | Circuit reluctance; Flux cutting; Induction motors; Magnetic circuits; Motive force; Search coil; Transformers |
| Footage description: | John Sparkes introduces the programme which will examine sources of magnetism, magnetic circuits, and magnetic flux. Sparkes uses a diagram of bar magnets and thin lines of flux in air to explain why like poles of magnets repel one another. Sparkes demonstrates with 2 bar magnets. Sparkes uses the diagram again to show how the introduction of iron at the poles, modifies the flow of the lines of flux so that like poles can come together without a repelling force. Sparkes demonstrates with 2 bar magnets. Peter Chapman with an experimental set up for monitoring EMF in a magnetic circuit with a moving search coil. EMF is monitored on an oscilloscope screen. John Sparkes aids in the experiment. An equation is deduced. Chapman demonstrates how change of flux can be induced without movement of the search coil but by completing the magnetic circuit with iron bars. EMF is again monitored on the oscilloscope screen. Sparkes with an electromagnet. He generates an EMF which is monitored on the oscilloscope screen. Alan Cooper explains: 1. Source of magnetism; 2. Reluctance; 3. Flux. He draws a diagram of a magnetic circuit as he talks and then tells how each can be quantified. Sparkes adds a piece of iron to his electromagnet to complete the magnetic circuit. An air gap is left and the iron is moved toward and then away from the magnet. EMF is monitored on an oscilloscope screen. Flux is increased as reluctance is decreased. Sparkes and Cooper place a secondary coil into the air gap. The EMF induced in the secondary coil is monitored with a volt meter. Sparkes and Cooper now vary the air gap precisely with plastic sheets of known thickness. They take measurements of the output voltage of the secondary coil and will plot these on a graph. Chapman draws an electric and a magnetic circuit board. He explains how the electric circuit can be used as an analogue for a magnetic circuit. Sparkes and Cooper show the graph on which they plotted the voltage from the secondary coil above. Chapman explains why the electric/magnetic circuit analogy is not quite correct. Alan Cooper discusses the importance of iron for completing magnetic circuits. He introduces the discussion on the induction motor. Sparkes with Arago's Disc and a working model of an induction motor. He shows a proper induction motor in which iron has been used to complete the magnetic circuit. Sparkes sums up the programme by stressing the importance of magnetic circuits in electromagnetic devices. |
| Master spool number: | 6LT/70274 |
| Production number: | 00521_2103 |
| Videofinder number: | 698 |
| Available to public: | no |
