Available online
Description
This programme describes some of the physical mechanisms reponsible for the electrostatic charging of a thundercloud and the subsequent precipitation and electrical discharges resulting in lightnin...g. The role of pointed objects which can intensify the electric field near them is also demonstrated. The programme starts with spectacular attempts to trigger lightning by firing wire trailing rockets into thunderclouds, much in the same spirit as Benjamin Franklin's attempts to prove the essentially electrical nature of lightning by flying a kite connected to the ground by conducting string. A simplified model of the build-up of electrostatic charge and its separation in a cloud lead to the conclusion that even under the most optimistic conditions, the electric fields generated in a thundercloud are not sufficient for lightning to occur. In the words of a research scientist, if we didn't actually observe lightning we would say that it couldn't happen. The students home experiment is used to plot the effect of a conducting sphere in distorting and intensifying local electric fields. A high voltage experiment demonstrates that when a water droplet is subject to an intense electric field, it forms a pointed tip from which an electric discharge can occur at a lower field than is required when it is spherical. This observation of the enhancement of electric field at points gives a clue to the tiny electrical discharges inside thunderclouds which must be a necessary build-up to lightning. Possible ways in which normally insulating gas can "break down" and become conducting is shown by animation, as is the "streamer mechanism" of short exploratory steps moving downwards to earth and forming a weakly conducting path immediately preceeding the massive lightning discharge build up to the cloud. The programme ends with pointed advice on lightning avoidance!
This programme describes some of the physical mechanisms reponsible for the electrostatic charging of a thundercloud and the subsequent precipitation and electrical discharges resulting in lightnin...g. The role of pointed objects which can intensify the electric field near them is also demonstrated. The programme starts with spectacular attempts to trigger lightning by firing wire trailing rockets into thunderclouds, much in the same spirit as Benjamin Franklin's attempts to prove the essentially electrical nature of lightning by flying a kite connected to the ground by conducting string. A simplified model of the build-up of electrostatic charge and its separation in a cloud lead to the conclusion that even under the most optimistic conditions, the electric fields generated in a thundercloud are not sufficient for lightning to occur. In the words of a research scientist, if we didn't actually observe lightning we would say that it couldn't happen. The students home experiment is used to plot the effect of a conducting sphere in distorting and intensifying local electric fields. A high voltage experiment demonstrates that when a water droplet is subject to an intense electric field, it forms a pointed tip from which an electric discharge can occur at a lower field than is required when it is spherical. This observation of the enhancement of electric field at points gives a clue to the tiny electrical discharges inside thunderclouds which must be a necessary build-up to lightning. Possible ways in which normally insulating gas can "break down" and become conducting is shown by animation, as is the "streamer mechanism" of short exploratory steps moving downwards to earth and forming a weakly conducting path immediately preceeding the massive lightning discharge build up to the cloud. The programme ends with pointed advice on lightning avoidance!
| Module code and title: | S271, Discovering physics |
|---|---|
| Item code: | S271; 08 |
| First transmission date: | 19-05-1982 |
| Published: | 1982 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:25:00 |
| + Show more... | |
| Producer: | Tony Jolly |
| Contributors: | Shelagh Ross; Steve Swithenby |
| Publisher: | BBC Open University |
| Keyword(s): | Ben Franklin; Conducting; Electrostatic charging; Leaders; Rain; Return stroke; Streamers; Thundercloud; Triggering lightning |
| Master spool number: | HOU3843 |
| Production number: | FOUS232P |
| Videofinder number: | 1787 |
| Available to public: | no |
