A BLAST FROM THE PAST USING MAGNETISM!!

By Nickey S. (period 1)

Remember the collection of VHS tapes that you used to have when you were little? Have you ever wondered how movie makers were able to record film on those thin plastic strips that flowed through the tape? Well it turns out that magnetism is behind this phenomenon!

As you can see in the diagram below, a long plastic strip is wound around the supply reel and is turned continuously moving the strip from the Supply Reel to the Take-Up Reel. The plastic strip is actually coated with a magnetizable powder called ferric oxide powder. Movie makers would record sound and visuals onto the tape recorder's head using electromagnetism which is created from a coil of wire wrapped around iron that can only be magnetized when an electric current goes through the wires. The Rotating Video-Head Drums on the VHS picks up electric signals from TV signals and as the tape goes past the recording heads, the signals are recorded from the electrical signal onto the head drums of the tape.This electromagnet has the ability to rearrange the magnetic ferric oxide powder on the tape strip into a specific pattern that eventually creates the movie. Signals from TV connection can only be imprinted if electromagnetism takes place. These signals are stored onto the tape and when the VHS tape is played it gives off the electric signals that it had previously stored and sends them through to the TV screen where the electromagnetic signals are interpreted and shaped on screen into the movie.



vhs-tape-diagram.png
This diagram is depicting what goes on inside a VHS tape and the flow of the magnetized strip.




Not only is magnetism used to record film but it is also used in the process of erasing memory from the VHS tape. The difference in erasing memory is that you do not need an electromagnet in order to erase everything, however electromagnets are generally the most common type of magnets used in erasing. Special strong magnets like super magnets which are the strongest types of permanent magnet that can be found can also be used in erasing (These magnets actually stick to the VHS cassette showing that there really are magnetic particles within the plastic cassette casing). These magnets draw out the recordings on the magnetic ferric oxide powder. The type of magnets that would be used depend on their gauss which is the unit used for measuring magnetic density. Regular magnets that can be found on refrigerators for example would be too weak in order to pick up the signals recorded onto the tape strip.

In the video link below you can see what a magnet does to the film of a VHS tape that has memory stored onto it.

(please watch from 3:27-5:15)



Who would have ever thought that while you were sitting on the couch watching a movie that inside the VCR player your video cassette was surging electromagnetic signals from the VCR to the TV??



SOURCES

Arnold, Thomas K. "What Happens If You Run a Magnet Across a Recording or VCR Tape? | EHow.com." EHow | How To Do Just About Everything! | How To Videos & Articles | EHow.com. Web. 15 Mar. 2011. <http://www.ehow.com/how-does_5139658_happens-across-recording-vcr-tape.html>.
Sexton, Timothy. "How Do VHS Tapes Work? | EHow.com." EHow | How To Do Just About Everything! | How To Videos & Articles | EHow.com. Web. 15 Mar. 2011. <http://www.ehow.com/how-does_4884244_vhs-tapes-work.html>.
Video Cassette Case Diagram. Digital image. VHSTODVD. 2010. Web. 15 Mar. 2011. <http://www.vhstodvd.com/history-of-vhs-tape.html>.